JoeWoodworker
JoeWoodworker Veneer
The Official Website of this Non-Professional Woodworker ™

Topics: Vacuum Pressing and Trouble-Shooting
Total Questions and Answers: 77
Additional Topics: Click Here
Last Update: 9/2/14

General Vacuum Press Questions

  1. I want to build the vacuum press. Which version should I build?
  2. How is vacuum measured, what is CFM, and how much vacuum is needed for veneering?
  3. Can you measure the total pounds of pressure under the platens in a vacuum bag?
  4. Why is the Excel 5™ system faster than the Project: EVS™ system using the same pump?
  5. What if I can't pull the required vacuum within 10 minutes? And what is so important about "10 minutes" any how?
  6. How long does it take to draw the full amount of vacuum inside the bag?
  7. What size vacuum system should I look for?
  8. Will quick-disconnect fittings for compressed air work with vacuum?
  9. Is it safe to use PVC for the vacuum reservoirs? What about ABS?
  10. What will happen if I make the vacuum reservoirs larger?
  11. Do I have to use the "dual reservoir" design or can I use a single reservoir of comparable volume?
  12. Do I have absolutely have to use a vacuum reservoir for my vacuum press?
  13. Why should I buy parts and build a press when there are other companies offering similar pre-assembled units for the same amount of money? And since this pump will run continuously, how long will it last?
  14. Are there any good books about vacuum pressing available?
  15. Can a vacuum press be used for flooring inlays and medallions?
  16. Does the vacuum valve have to be attached to the vacuum press? Can I attach it to the lock-on connector instead?
  17. What else could I use for the reservoirs besides PVC?
  18. Is it difficult to find the schedule 40 PVC for the reservoirs?
  19. How long does a "recharge" cycle last when the vacuum inside the system drops?
  20. I live at 5,000 feet above sea level. What effect will that have on my vacuum pump?
  21. How often should my auto-cycling vacuum press recharge the vacuum level?New

Electric Vacuum Press Questions

  1. Where can I find a vacuum pump?
  2. Can I use a small vacuum pump for an auto-cycling vacuum press system?
  3. I already own a vacuum pump. What do I need to use it for vacuum pressing?
  4. Why do I need the vacuum controller, gauge, reservoirs and other parts to build the EVS system?
  5. What kind of pump will work for a vacuum press?
  6. What is the problem with rotary vane pumps?
  7. What if I want something simple or if I want it run continuously?
  8. I've heard that some vacuum presses have a 'quick pull-down' scheme that allows you to release and quickly re-evacuate the press for minor adjustments. How can I accomplish this on my vacuum system?
  9. What's the purpose of the bleeder valve on the continuous-run systems?
  10. Is there a way to make the auto-cycling press run continuously?
  11. I bought a 220v Gast vacuum pump from "surplus center". Will this work for vacuum pressing? Do I need and special parts to make it work.

Air Powered (Venturi) Vacuum Press Questions

  1. With the Project: V2 system, will my air compressor run continually?
  2. How much air does the venturi version of the press require?
  3. Is a venturi system better than an electric pump system?
  4. Harbor Freight has a venturi pump rated at 28.3" of mercury and 4.2 CFM for only $17. Could this be used for a vacuum press? 
  5. What do I do if my air compressor can't keep up with the venturi on my vacuum press?
  6. How many licks does it take to get to the center of a Tootsie Roll Pop?
  7. I want to build the Project: V2 Premium system but I don't want the full kit. Do you offer the Premium version of the Mac valve and venturi separately?
  8. I've heard that multi-stage venturi units are the best vacuum generators. Is that true?
  9. Can I use the intake port on my air compressor to generate vacuum?
  10. Do you offer a kit to upgrade the V2 kit to the V2 Premium?
  11. Is there a major difference between the V2 Plus and the Premium 5 for large vacuum bags? New

Vacuum Bagging Questions

  1. Since vinyl for bag making is only 54" wide, what should I do if I need a vacuum bag that is 6' wide?
  2. How can I build a vacuum frame press?
  3. What is the difference between vinyl and polyurethane for vacuum bags?
  4. I'm on a budget and need to find a cheaper material for the vacuum bag. Any suggestions?
  5. Can I use Space Bags™ and a Food Saver™ for veneering?
  6. It's difficult to get everything into my large vacuum bag. What do you suggest?
  7. What can I do to make my plastic bag closure easier to snap onto the bag?
  8. How do I attach my existing vacuum press to the DuraMax vacuum bag?
  9. Can I press multiple projects in a single vacuum bag at the same time?
  10. What size bag can I use with my vacuum press?
  11. Why does it seem like your platen/caul system is different from everyone else's?
  12. Why do I have to leave the bag connected to the vacuum press after it pulls the full vacuum?
  13. How is the CFM of the vacuum source related to the size of the vacuum bag?
  14. Where can I find a 4' x 8' vacuum bag with the opening on the long side of the bag?
  15. How can I determine if my project is too wide or tall for a vacuum bag?
  16. Will I foul the finish if a coat of paste wax is applied to my platens?
  17. How do I know that I'm buying a decent vacuum bag?

Miscellaneous Questions

  1. I'd like to use a refrigerant compressor from an old air conditioner. How do I make the connection from the compressor to the first part of the vacuum press?
  2. What kind of refrigerant compressor (from a refrigerator, freezer, etc.) works best and what brand should I look for?
  3. I'd like to use a refrigerant compressor for my system. Will the lack of oil in a compressor pump cause the unit to eventually burn out?
  4. Do you have any information about converting copper tubing to work with threaded fittings?
  5. When vacuum clamping, how do I ensure a good seal on porous woods like mahogany?
  6. How do I connect one of the VeneerSupplies.com vacuum presses to a OneWay vacuum chuck?
  7. Can I use a venturi system for vacuum chucking on a wood lathe?
  8. What is your favorite kind of cookie?
 

Troubleshooting

  1. I hear air leaking from the bag stem connector. What should I do?
  2. D'oh...I punctured my vacuum bag or I have a leak somewhere. How do I fix this?
  3. How do I make my vacuum bag last as long as possible?
  4. How can I test my vacuum press for leaks?
  5. My system appears to be leaking vacuum. What should I do?
  6. I just wired my system as shown in the directions and it's not turning on. What should I do?
  7. How do I reset the vacuum gauge so the needle reads zero when there is no pressure on it?
  8. My system is complete and it holds pressure perfectly after the pump cycles off but it takes a long time for it to shut off and I can't get it any higher than 21" of Hg. Why is that? 
  9. My system was running fine for years but recently it started to cycle on and off very frequently. How do I fix this?
  10. My glycerin-filled vacuum gauge has an air bubble in it. Is it defective?


General Vacuum Press Questions

G1: I want to build the vacuum press. Which version should I build?

It really depends on a wide array of factors. Here are some questions that must be answered. Each question is also a link to a page which will help you decide.

  1. Do you want a system that cycles on/off automatically or one that runs continuously?
  2. If you want your vacuum press to cycle on/off, do you want it to be powered by electricity or by compressed air?
  3. What is the maximum project size you estimate that you will want to put in a vacuum bag?
  4. Will your projects primarily be flat or curved?

Check out this link which contains a chart of the systems offered at VeneerSupplies.com. This chart discusses all of the critical aspects of selecting a vacuum press system.

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G2: How is vacuum measured, what is CFM, and how much vacuum is needed for veneering?

In vacuum veneering, the vacuum level is usually measured in terms of inches of mercury (" of Hg).

CFM or "cubic feet per minute" will only describe the speed at which the vacuum is created. It is a measurement of the amount of air volume that can be moved within a specified time frame. The "CFM" rating will not give you an idea as to the maximum possible vacuum.

For vacuum veneering, you'll need a minimum of 18" of Hg. However, the recommended pressure for most adhesives is 21" of Hg.

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G3: Can you measure the total pounds of pressure under the platens in a vacuum bag?

The total pressure can be calculated by the vacuum (in Hg) multiplied by .5. Then multiply this number by the total square inches of one platen. Therefore, if you are applying 23" of Hg to a platen that is 1'L x 2'W, the calculation is as follows:

23 x .5 x 288 = 3312 pounds of force.

For more information, see this chart.

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G4: Why is the Excel 5™ system faster than the Project: EVS™ system using the same pump?

According to the VeneerSupplies.com Vacuum Press Chart, the Excel 5 system evacuates a vacuum bag faster than the Project: EVS system using the same Gast vacuum pump. The Excel system is very efficient with air flow and has less restricting parts than the EVS system. The EVS system has a manifold, Mac valve, check valve and vacuum reservoirs which air flows through. These extra pieces slightly reduce the speed of vacuum flow into the pump.

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G5: What if I can't pull the required vacuum within 10 minutes? And what is so important about "10 minutes" any how?

Ten minutes is the average amount of time that most users will have to get a project under vacuum before the veneer glue starts to set up. If the glue starts to set up before decent pressure is on the project, the veneer may not adhere correctly. Typically, the problem is a poor bond that doesn't show up until you apply a finish. The other remedy is to get a faster pump or a smaller bag to minimize the risk.

If you can't get the pressure on the project within 10 minutes...

  • Work faster
  • Use a smaller vacuum bag
  • Use a slower setting glue like Ultra-Cat™
  • Temporarily cool the air in the work shop (to slow down the glue "flash")
  • Add an additional pump
  • You can also use a Shop-Vac to pull some of the bulk air when using exceptionally large vacuum bags. The easiest way to do it is to tee in a ball valve to the vacuum line (between the reservoir and the bag). Then you'll need to rig up a few fittings to mate the Shop-Vac hose to the vacuum line. Most Shop-Vacs will only pull about 1.75" of Hg (provided the filter is clean) but this low pressure air in your bags could be a lot of volume and waste a lot of core vacuum time by the pump. As soon as the bulk air is removed, close the ball valve, then shut off the Shop-Vac (in that order).

    For an idea on building this contraption, see the box below.

From a vacuum press builder in Naperville, Illinois ...

"...I started out in the tool department, with an air compressor tee and connectors (I had trouble finding them, but Coleman makes them). Then I moved to plumbing and got a ball valve and a series of adapters to go from 1/4" to 1" pipe. Finally, I ended up finding a piece that's meant for a dishwasher connection that will let me connect the whole mess to my Fein shop vac with duct tape."

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G6: How long does it take to draw the full amount of vacuum inside the bag?

The length of time required to draw a full vacuum inside the bag will vary from one system to another. The speed of the pump is the most important factor. The "draw down" times for the vacuum presses offered at VeneerSupplies.com are listed on this chart.

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G7: What size vacuum system press should I look for?

Maximum pressure is the first critical factor. The vacuum source must be able to pull at least 18" of Hg. The second factor is air flow which determines the maximum size of the vacuum bag suitable for your system.

Project Minimum Requirements  
4' x 4' or less vacuum bags 1 CFM for flat panels 3 CFM for curved panels
4' x 6' to 4' x 8' vacuum bags 3 CFM for flat panels 5 CFM for curved panels
Vacuum clamping .5 CFM for non-porous materials 3 CFM for porous materials
Vacuum chucking on a lathe 1 CFM for very small projects 3 CFM for small/medium projects

More information about this topic can be found at this link.

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G8: Will quick-disconnect fittings for compressed air work with vacuum?

Unfortunately, most quick-disconnect fittings will not work with negative pressure.

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G9: Is it safe to use PVC for the vacuum reservoirs? What about ABS pipe?

PVC Info Yes, PVC pipe that meets ASTM D1785 or D2241 standards can withstand vacuum. According to research conducted by Dr. R.K. Watkins at Utah State University, vacuum levels cannot collapse PVC pipe that is exposed to normal service temperatures. In fact, quick calculations show that even under conditions of elevated operating temperatures of 100oF, the pressure required to collapse most PVC pipe is greater than atmospheric. In other words, the pipe can withstand a complete vacuum. For more information, please see this article from the Uni-Bell PVC Pipe Newsletter.

Cell Core PVC
Sometime called "hollow core" PVC, Cell core is not recommended for vacuum.

Schedule 80 PVC
Solid core schedule 80 PVC can also be used for vacuum according to George Fischer Piping Systems. Click here to see their conclusion. The full article can be found by clicking here.

ABS Pipe
After a phone conversation with a tech a Uni-Bell, I can not recommend ABS pipe for the vacuum reservoirs. It may be unsafe for vacuum. However, some users have not followed this advice and used ABS anyhow. None of these users has contacted me indicating a problem and there are pictures on the vacuum press gallery page of systems built with ABS pipe. It would appear that ABS 2112 and ABS 1316 could possibly withstand vacuum. See this page for details.

More PVC InfoAbout Uni-Bell
Uni-Bell has served the engineering, regulatory, public health and standardization communities with integrity and considerable measures of both time and resources. Whenever questions have arisen relative to PVC pipe performance, Uni-Bell members, through their Association, have responded. Pipe designers and installers have been provided with much needed research from Uni-Bell regarding pipe deflection, ultraviolet aging, tapping, cyclic surge performance, in-service durability, and safety.

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G10: What will happen if make the vacuum reservoirs larger?

A larger vacuum reservoir system will do two things.

  1. It will give you a slightly faster initial pull-down on the vacuum bag as long as you pre-charge the reservoirs before opening the valve to the bag. Keep in mind that if the bag is large, there may be no gain in the initial pull-down speed because the larger vacuum reservoir will require even more air volume that the pump must evacuate.
  2. A larger reservoir will lengthen the amount of time between cycles but it will also make the recharging cycles take longer. Conventional wisdom says that the vacuum press should be more durable if it cycles on less often but the truth is that the moving components on the Mac valve and vacuum switch are rated for a hundred thousand cycles or more. So the benefit of the larger tank isn't really earth shattering.

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G11: Do I have to use the "dual reservoir" design or can I use a single reservoir of comparable volume?

There is no problem changing the tank design from a dual to a single reservoir design. You could also use a triple or quad reservoir design if you wish.

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G12: Do I have absolutely have to use a vacuum reservoir for my vacuum press?

The vacuum controller I offer can be used without a vacuum reservoir. To do this, the vacuum level is measured from inside the vacuum tube. You just need to make a "T" connection in the vacuum line.

However, I highly recommend using a reservoir. The vacuum reservoir serves as a buffer zone (or a backup for vacuum). Without it, your system will constantly turn on and off. This will lead to premature failure of any pump.

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G13: Why should I buy parts and build a press when there are other companies offering similar pre-assembled units for the same amount of money? And since this pump will run continuously, how long will it last?

Despite that fact that each system achieves similar results, there is an inherent quality difference between them. I've seen many of the low-tech vacuum systems in operation and they all work well but their systems consist of a generic imported vacuum pump and cheap accessories. The pumps that we (VeneerSupplies.com) offer are made in the USA and have rebuild kits that the manufacturers have promised to offer for a minimum of 10 years. In fact, Gast has been using the same filters, valves, and gaskets on their pumps since 1981!

Additionally, our press parts are all nonproprietary so you can add and modify the unit as needed. For instance, with our kit, you can build a vacuum bag in any size you want and still connect it easily to the pump system. With bags from other manufacturers, you are limited to the sizes they stock and should they ever change the bag connector design, you may not be able to add future bags if one were to go bad.

Our nonproprietary parts allow you to attach additional bags with simple T-fittings found at the hardware store. Our system is also easily adaptable for use with vacuum clamping and templating.

Overall, you get the same end result with either system (ours or theirs) for about the same amount of money. Our system requires a bit of your time, but it includes heavy duty components adapted from other industries (at industrial level specs); not imported parts that were assembled trying to maintain a healthy margin. A good example of this is our vacuum gauge. On other systems, a plastic dry gauge is used. This causes needle flutter which makes reading the gauge impossible. Our stainless steel gauge is glycerin filled so the needle doesn't flutter and you can see exactly what pressure is in the system.
Vacuum Gauge Flutter
Needle Flutter
(What pressure is it reading?)

And unlike the bare-bones kits that our competitors offer, our Excel Vacuum Press system has a fully adjustable vacuum range for delicate projects. You can dial it in for any pressure from 840 to 1750 lbs of pressure per square foot.

The truth is that we don't have the "overhead" as other companies. We ship website orders from a small rented warehouse so we don't need the high financial return from the sale of the systems and components. So what you get is a heavier duty system at the same price that can be modified and adapted as your veneering skills expand. For more information, check out this page... "Why Build A Vacuum Press"   

  Excel Vacuum Pressing System . Generic Vacuum Press Kit
Pump Gast 1.1 CFM   Unknown
Tubing 1/2" O.D. double-braid reinforced vinyl   5/16" O.D. vinyl
Filter High-efficiency, high-flow, pleated filter   None (!)
Adjustable Yes: fully adjustable to prevent crushing and starving the glue surface   No. User must use full force.
Pressure 560 to 1700 lbs/sqr ft.   1700 lbs/sqr ft.
Gauge Stainless steel with liquid filling   Plastic
Bag Connection Brass lock-on connector   Vinyl friction fit
Bag Included Several sizes of 30 gauge bags are available starting at under $40   4' x 4'
20 mil thick
Clamping Kit Available for under $25   Not available
Where to Buy VeneerSupplies.com   Rockler, Woodcraft, etc.
Retail Price $296.50   $339.00

How long will the pump last?

The manufacturer says that if the pump were left running continuously, it would be two years before it would need to be rebuilt.

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G14: Are there any good books about vacuum pressing available?

Yes! There are three exceptional books on veneering that would make great additions to a woodworking library.

The Complete Manual of Wood Veneering by William Lincoln
It reads more like a high school text book than a "manual" but it is very thorough and well organized. It's currently out of print but it does show up on Ebay rather often.

Mike Burton BookVeneering: A Foundation Course by Mike Burton
This book was out of print and hard to find for quite a while but it was revised and published again in June of 2006. The new version includes a section on marquetry which was a great complement to the other chapters. Mike Burton covers various forms of veneer application including vacuum pressing, iron-on veneering, and more traditional methods. The book also includes a few well designed veneering projects. One thing that I really enjoyed is the author's down to earth writing style. He writes as if he was speaking directly to you and his comments are insightful and often downright hilarious.

Jon Benson BookWoodworker's Guide to Veneering & Inlay by Jonathan Benson
I have admit that this book is probably going to be one of the de facto standards for veneering guides. The author clearly explains nearly every aspect of veneering from log to finished project without over-stressing any particular concepts. This keeps the reading enjoyable, interesting, and wonderfully helpful. If you're interested in vacuum bagging your veneered projects, Jonathan Benson's book has it covered.

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G15: Can a vacuum press be used for flooring inlays and medallions?

Yes. I've helped several inlay and medallion craftsmen build a frame press system for this purpose.

Since some species of wood used for flooring are porous, air will leak into the system. If you have a cycling vacuum press such as the Project: V2 or EVS system, you can easily wire in a switch to convert it to run continuously. See FAQ E10 for details.

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G16: Does the vacuum valve have to be attached to the vacuum press? Can I attach it to the lock-on connector instead?

Lock On Connector ModYes! Since the threads on those fittings are the same (1/4" NPT) you can easily move the vacuum valve from the system to the lock-on connector. This requires no additional parts and simplifies the process of vacuum bagging by allowing you to open the vacuum flow from the vacuum press immediately after you connect the lock-on connector to the bag.

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G17: What else could I use for the reservoirs besides PVC?

There is no easy and safe answer to this question. I have seen vacuum press reservoirs made from fire extinguishers, scuba tanks, air compressor tanks, ABS plastic, aluminum tanks, and many other materials. Ultimately, the question is of safety. None of these are considered safe for vacuum unless the manufacturer specifically says so.

The only affordable material that is scientifically proven to be safe for vacuum is schedule 40 or 80 solid core PVC.

Thanks to Troy Delnicki of Faribanks Alaska for this tip...
If your local hardware store does not have 3" schedule 40 PVC in the plumbing department, check the electric aisle instead. They might have schedule 40 PVC in electrical conduit (gray) which is very affordable. Then just get the white schedule 40 PVC caps in the plumbing aisle.

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G18: Is it difficult to find the schedule 40 PVC for the reservoirs?

In the eastern and midwest areas of the US, schedule 40 PVC pipe can be found at most plumbing suppliers. I have heard from several west coast residents that schedule 40 PVC can only be found at "specialty" plumbing dealers.

Canada appears to have a good supply of schedule 40 PVC.

Schedule 40 PVC pipe is not available in Australia. I have been advised that the Australian equivalent is Class 12 Water Pressure Pipe. Only specialty irrigation/pipe centers handle it. It is rather expensive so consider purchasing the PVC kit from the VeneerSupplies.com website to save a few bucks.

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G19: How long does a "recharge" cycle last when the vacuum inside the system drops?

There is no accurate answer to this question but it's probably not that important since the recharge cycles are generally very short. I have a venturi powered system that only take 5 seconds to recharge my 4x4 vacuum bag. I also have an electric vacuum system that take 30 to 40 seconds to recharge. In either case, it's not a long enough cycle to cause concern.

The length of the recharge cycle is affected by

  • The sensitivity (dead band/differential) of the vacuum switch
  • The size of the vacuum bag
  • The size of the vacuum reservoirs

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G20: I live at 5,000 feet above sea level. What effect will that have on my vacuum pump?

The general rule of thumb is a loss of 1" of Hg for every 1,000 feet above sea level. A pump that delivers 25" of Hg, will actually provide 20" of Hg at 5,000 feet above sea level. This pump would be fine for vacuum veneering but you might find that it takes more time to achieve 20". In that case, simply turn back the shut-off point on the vacuum controller. A setting of 17" to 18" of Hg will still yield a good veneered panel. For a more detailed chart describing the effects of altitude on vacuum levels, please click here.

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G21: How often should my auto-cycling vacuum press recharge the vacuum level?

With my own vacuum press system, the system recharges every 60 to 75 minutes when not attached to a vacuum bag. Some users have reported that their systems recharge every 10 to 15 minutes and others have said they could go an entire day without recharging. It's important to remember that when the system is attached to a vacuum bag, the cycle frequency will increase. How much of an increase depends on several factors such as bag size, age of the bag, and how well the closure is attached to the bag.

So, what is an acceptable frequency of vacuum recharging? That really depends on you. Some users spend a lot of time tracking down sources of leaks. They are often successful. Other users are fine with the system recharging more frequently. It's all just a matter of personal preference.

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Electric Vacuum Press Questions

E1: Where can I find a vacuum pump?

Vacuum PumpOf course, I offer pumps at the VeneerSupplies.com. You can also look on the Internet for "used vacuum pumps". Be careful with used and salvaged units because vacuum pumps can be used in a variety of hazardous conditions such as use from medical and toxic waste disposal.

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E2: Can I use a small vacuum pump for an auto-cycling vacuum press system?

Project CRS KitYou can use a reservoir based system (and the vacuum controller) with any pump. But there is no problem with letting smaller pumps run for the whole time the veneer is being pressed. Most of these pumps are designed to run continuously and they use very little electricity while running. VeneerSupplies.com offers a kit to turn just about any pump into a continuously running vacuum press system with full pressure adjustment. Click here for details.

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Vacuum Press IdeaE3: I already own a vacuum pump. Will it work with the Project: EVS system?

The Project: EVS kit allows you to create an auto-cycling vacuum press system with your vacuum pump. The instructions for the kit can be found here.

If your vacuum pump meets the specifications below, then it will work with the Project: EVS kit and can be used with a maximum bag size of 4 x 8. Most of the manufacturers have great customer service and if you provide them with the model number of your pump, they can give you these specifications:

Specification Description
Ideal Spec
Port Size The thread size of the vacuum and exhaust ports
1/4" NPT
Maximum Vacuum The max vacuum level expressed in "inches of Mercury" (or Hg)
21" Hg
Start-Up Amps The amperage draw when the pump first starts up
< 10
Vacuum Flow The flow of air (or CFM) at 0 pressure
3 +

Project EVS KitPort Size: Make sure the vacuum port on the pump has 1/4" NPT threads. The kit is designed to use this thread size. If your pump has a different thread size, you'll need an adapter to change it to 1/4" NPT. These can be found at most hardware stores.

Maximum Vacuum: Generally speaking, 18" Hg is the minimum vacuum level for veneering. However it's ideal to use a vacuum pump capable of at least 21" Hg. If you are more than 1,000 feet above sea level, even more vacuum is needed.

Vacuum Controller RelayStart-Up Amps: Some vacuum pumps will have a label displaying the running /operating amperage. However, the most important specification is the "start up" amperage. The vacuum controller on the EVS kit will handle up to 10 amps. If your pump draws more than 10 amps at start up then you must use a relay to handle the high-current switching. In most cases, the start up amperage is three times the running amperage but you will have to confirm this with the manufacturer of your vacuum pump.

Vacuum Flow: If your pump has a flow rating of more than 4 CFM, you will need to add a vacuum damper to prevent the vacuum controller from turning on and off rapidly. This chattering will quickly damage the pump. Keep in mind that your vacuum pump's CFM rating effects the maximum bag and project size. Learn more by clicking here.

Additional Notes
Based on experience, I do not recommend rotary vane vacuum pumps. I have found them difficult to fine tune for vacuum pressing and they draw a tremendous amount of power when they start up. There are much better choices in vacuum pumps than rotary vane.

Oil-bath pumps that are typically used for refrigerant systems can also be problematic. This type of pump has a tendency to emit a plume of oil mist into the air. For most users, this can be a huge issue that causes problems with the finish that is applied to the veneered project or any other unfinished project in the vicinity of the pump.

If you thought you had the perfect pump, but now you are not certain, consider getting a rebuilt Thomas pump on the VeneerSupplies.com. They are very affordable and quite reliable. I've had a ton of great comments about these pumps.

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E4: Why do I need the vacuum controller, gauge, reservoirs and other parts to build the EVS system?

In a perfect world, you'd only need to connect the intake of the vacuum pump to a tube which would be connected to a vacuum bag to have a working vacuum press. All of the "extras" on the Project: EVS and V2 systems might seem a little unnecessary but each has a place and purpose on an auto-cycling system.

The Vacuum Gauge
Obviously, the gauge shows the user the vacuum level inside the system. More importantly, it shows the user if there is a leak. When the system cycles off, the needle on the gauge will move subtly, but it's enough to indicate when a leak is present.
Vacuum Gauge

The Vacuum Controller
Without this piece, the system would run continuously. This is fine if you don't mind the 74 decibels of sound being continuously emitted from the pump. Or if you are not bothered by the waste of electricity from a pump that has to run for the entire duration of the pressing. The vacuum controller monitors the vacuum level and cycles the system on and off as needed.
Vacuum Controller

The Vacuum Reservoirs
If you are going to have a system that cycles on and off, you certainly don't want it to cycle too frequently. This is bad for the pump and it's just plain annoying. The reservoirs hold spare vacuum just like scuba tanks hold air for divers. If you have an air compressor in your shop, you certainly understand that a larger tank on an air compressor means that it will cycle on less frequently. The same is true of the vacuum reservoirs.
Vacuum Reserviors

The Vacuum Valve
The vacuum valve allows you to pre-charge the reservoirs with vacuum which will give you a short burst of vacuum in the initial pull-down of the vacuum bag.
 
Vacuum Valve

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E5: What kind of pump will work for a vacuum press?

Rebuilt Vacuum PumpAny vacuum pump that can pull 21" of hg will work with the system. Vacuum presses can be made from oil bath, diaphragm, and piston based pumps. Based on experience, I do not recommend rotary vane vacuum pumps. I have found them difficult to fine tune for vacuum pressing and they draw a tremendous amount of power when they start up. There are much better choices in vacuum pumps than rotary vane.

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E6: What is the problem with rotary vane pumps?

Rotary vane pumps run hot and if your vacuum bag has a leak, the pump will run nonstop and could over-heat. Most rotary vane pumps have a thermal protection circuit that shuts off the pump if the system gets too hot. A leaky bag plus a shut-down pump equals a failed veneer panel. The vanes used in this type of pump are fragile and debris going through the vanes is potentially troublesome because the tolerance in the vane housing is very tight. A service tech at Thomas Pumps sent me an email saying they had seen failures caused by the vanes getting gummed up with chemicals off-gassed by certain adhesives. He had never seen a piston or diaphagm pump with this type of trouble.

I am aware that almost every vacuum press manufacturer is using a rotary vane pump and I'm not saying anything bad about those systems. My experiences with our customers and my own vacuum press systems are all good ones. I've stuck with piston and diaphragm pumps for 8 years eventhough I've had the opportunity to buy hundreds of rotary vane pumps for pennies on the dollar.

My opinion is that rotary vane pumps are very durable when used for the right application but in a dusty workshop, a piston or diaphragm pump will end up being a workhorse that can pull through the wagon through the mud.

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E7: What if I want something simple or if I want it run continuously?

Consider the Project: CRS builder's kit or the Excel 1 vacuum press system offered at VeneerSupplies.com.

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E8: I've heard that some vacuum presses have a 'quick pull-down' scheme that allows you to release and quickly re-evacuate the press for minor adjustments. How can I accomplish this on my vacuum system?

Click here to orderAll of the auto-cycling kits offered at VeneerSupplies.com come with a vacuum valve that is used between the reservoir and the vacuum tube that attached to the vacuum bag. You can close the valve and turn on the vacuum press to pre-charge the reservoirs with vacuum.

If your project is not sitting properly inside the vacuum bag, you can easily shut off the vacuum without losing the pressure inside the reservoirs. You can then re-adjust the material and re-connect the bag to the system. After you open the vacuum valve, the buffer of vacuum will then transfer to the bag and give you a short burst of vacuum. Of course, the press will start to recharge the reservoirs almost immediately but at least you still get that faster initial pull down.

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E9: What's the purpose of the bleeder valve on the continuous-run systems?

Bleeder ValveThe bleeder valve serves several functions. The core reason is that it allows you to easily adjust the pressure in the system. But it’s important to note that the bleeder valve also allows the pump to circulate a little bit of fresh air through it so any off-gases from adhesives are allowed to escape.

The pumps are continuous duty, but they can generate some heat which can cause the off-gases to create a build up of residue. This residue will clog the head-valve inside and reduce the efficiency of the pump. And eventually, the residue will harden the flexible surface of the diaphragm and cause it to crack prematurely.

Piston based pumps are also prone to residue build up which can cause the pump to over-heat as the friction on the cylinder walls builds up.

There are several companies offering continuous-run system but few (if any) offer a bleeder valve with the system. My gut feeling is that they don't offer it because they feel the system will not be used frequently enough to warrant the expense of the valve.

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E10: Is there a way to make the auto-cycling press run continuously?

Yes, it's quite simple to make a cycling vacuum press run continuously. Simply wire a switch that jumps the connection between to the common and normally closed terminals on the vacuum controller. A standard light switch will work fine for most systems. When engaged, the light switch will bypass the vacuum controller's switching and allow the electrical current into the system regardless of the vacuum level in the reservoirs. When disengaged, the system will return to auto-cycling on and off to maintain the pressure set by the vacuum controller.

Follow up question
Why would you want this option?

Unnecessary stresses are placed on a pump if it cycles on and off too frequently. If you are using the vacuum press system for vacuum chucking or vacuum clamping and the system is cycling on and off very often (every 30 seconds), you might wish to consider this option.

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E11: I bought a 220v Gast vacuum pump from a "surplus center". Will this work for vacuum pressing? Do I need any special parts to make it work?

The answer to the first part of the question is maybe. About half of the builders of the the Project: EVS kit that use the Gast 220v rotary vane style pump from a "surplus center" are reporting moderate to severe difficulties in getting the press to cycle on and off. To maximize your chances of success, I offer these suggestions:

Vacuum Damper Fitting Be certain to use the vacuum damper on the vacuum controller. I offer an incredibly precise damper to prevent the rotary vane pumps from chattering on and off at the end of a charging cycle.

Minimize the amount of tubing between the pump and the check valve.

Use a dedicated vacuum filter with a minimal amount of air space inside. In other words, do not use the titanic filters that some surplus centers are offering.

To answer the second part of the question...

The vacuum controller we offer will handle up to 10 amps at 220v but keep in mind that the start-up amps on the pump can be three times more than what is stated on the pump's name plate. You will also need a 220v Mac valve to make the system work correctly. We have them in stock at no additional cost over the standard voltage Mac valve. To order one with a builder's kit, simply mention that you need the 220v Mac valve in the comments section at the end of the check-out process.

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Air Powered Vacuum Press Questions

A1: With the Project: V2 system, will my air compressor run continually?

No. Think of it this way... the Mac valve is a gate that controls the flow of air from the air compressor only when the vacuum controller recognizes the need for additional vacuum. The venturi pulls vacuum very quickly. In fact the reservoirs tanks will achieve full vacuum in just 20 seconds. After that, the compressed air is shut off automatically.

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A2: How much air does the venturi version of the press require?

Model
Vacuum Flow
Air Requirement
Mini™
.8 CFM
1.80 CFM
Basic™
1.2 CFM
2.1 CFM
Plus™
3.2 CFM
4.8 CFM
Premium 5™
5.5 CFM
7.8 CFM
Premium 9™
9 CFM
12.5 CFM

 

 

 

Smaller air compressors may require a separate reserve tank that will easily piggy-back to your existing tank and give you more pressure in reserve to get the initial vacuum created in the bag. If the pressure coming out of the air compressor drops below 80 PSI, the air coming out of the compressor will just be wasted. It really needs the full 80 PSI to work correctly.

The temporary fix is to manually shut off the venturi press until the compressor has reached 80 PSI, then turn the system back on and let it generate vacuum again until it is below 80 PSI. By doing this, it may take longer to pull a full vacuum but you will not lose any noticeable vacuum inside the system because of the check valve.

The venturi units can handle up to 120 PSI but the recommended pressure is 80 to 105.

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A3: Is a venturi system better than an electric pump system?

Both systems work nearly identically but there are some details that might swing your vote in one direction or another. The venturi systems are easier to build, cost less, and have less moving parts. Additionally, you'll find the a 3 CFM venturi can draw a full vacuum faster than a 3 CFM electric vacuum pump. Click here for more information.

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A4: Harbor Freight has a venturi pump rated at 28.3" of mercury and 4.2 CFM for only $17. Could this be used for a vacuum press? 

I have tried that same venturi with a vacuum press for several years before I realized how inefficient it was. In May of 2005, I sent one out for lab testing and the results were surprisingly disappointing.
  • First, HF rates it at 4.2 CFM. This the air consumption, not the vacuum flow. What's important is that the true air consumption was almost 8 CFM.  In fact, I sent them two more units for testing because I thought the first venturi I sent had to be defective. It wasn't. They all gulped up 8 CFM of air to pull full vacuum.
  • Second, they only pulled between 1.75 and 2.05 CFM of vacuum flow. That's a loss co-efficient of 75 percent.
  • Lastly, there is absolutely no way to muffle the horrendous sound that these emit without further reducing its capability.

I was hesitant to add this to the FAQ but I don't want to see anyone waste their money with the HF venturi. I know it may sound like I'm just trying to be "Joe Salesman" but honestly, the HF unit is not worth the savings over buying the new model venturi that's on the VeneerSupplies.com website.

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A5: What do I do if my air compressor can't keep up with the venturi on my vacuum press?

Find the air consumption requirement before purchasing a venturi-based vacuum press. Then make sure your air compressor's output capacity meets or exceeds this required flow level. If your air compressor falls slightly short of the venturi needs,
you can "baby sit" the system. Here's how...

Watch the compressor gauge and when it drops below 80 PSI, turn off the vacuum press until the air compressor gets back to at least 90 PSI. The venturi stops creating vacuum when the incoming air pressure drops below 80 PSI. At that point, the air coming out the compressor is simply wasted. Turn the vacuum press on again after the compressor has achieved at least 90 PSI.

Once the vacuum press cycles off by itself, it won't use much air from the compressor to recharge the vacuum so you won't have to baby sit it any longer.

Learn more about the Project: V2 air compressor requirements on page 2 of this link.

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Mr. OwlA6: How many licks does it take to get to the center of a Tootsie Roll Pop?

Let's find out.
One. Two-ooo. Three.

Three!

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A7: I want to build the Project: V2 Premium system but I don't want the full kit. Do you offer the Premium version of the Mac valve and venturi separately?

I do offer the individual Premium Mac valve separately. But I've found that some builders use the wrong parts in conjunction with it. This doesn't allow the venturi to work at its fullest potential. For instance, some builders tried to power the venturi with a Mac valve that was too small. Other builders used tubing that was too small. And some were using check valves with rigid springs that didn't work well with vacuum.

This only led to me receiving countless emails with complaints that the system didn't work well (or at all). After hours of troubleshooting and answering emails, I always found it was because the builder was mismatching parts and bottlenecking some part of the system.

The venturi is the most expensive part of the system. I've had to commit to buying an outrageous amount of them to get a good price for everyone. The kits are designed to save you as much money as possible and provide me with just a few bucks that I use to compensate myself and my wife for the tremendous amount of work that we are putting into the website. In the long run, I'm sure you'll find the kits are very well priced and that the Mac valve and venturi bought separately would cost nearly as much as the whole kit. But if you absolutely need the Premium venturi only, they are available on the VeneerSupplies.com website.

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A8: I've heard that multi-stage venturi units are the best vacuum generators. Is that true?

A multi-stage or multi-chamber vacuum pump is made up of 2 to 4 separate in-line venturi’s that work in sequential stages using the same input air supply. Each chamber is designed to function up to a specific vacuum level. When a chamber reaches a prescribed vacuum level, a flap automatically closes off that chamber. This process continues until only the first chamber is drawing vacuum, thus the multi-stage effect. Learn more by clicking here.

Vac Pro VenturiWhat’s important to note is that most vacuum lifting applications work above 9" Hg. Typically, chambers 2, 3, and 4 have shut down before reaching 9" Hg, the multi-stage pump literally turns itself into an inefficient single-stage pump. The problem with the multi-stage pump is that it must maintain a high velocity of flow in chambers 2-4. Air consumption remains high, even though vacuum flow has decreased by almost 75%. In addition, if a vacuum filter is not used, and debris or dust enters the multi-stage pump, it can clog the flap valves requiring repair and/or replacement, downtime and loss of production. The Vac Pro units are highly efficient single stage vacuum generators. In most cases, the Vac Pro flow rates at the upper levels exceed multi-stage pumps by a factor of 2 to 7 times, while air consumption remains constant!

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A9: Can I use the intake port on my air compressor to generate vacuum instead of using a venturi?

According to Campbell Hausfield, that would be a big mistake. The internal valves will eventually bend if there is back pressure against the intake. This will lead to poor compressor performance and eventually total valve failure.

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A10: Do you offer a kit to upgrade the V2 kit to the V2 Premium?

Yes. There is an upgrade kit to convert your existing V2 or V2 Plus vacuum press to a V2 Premium.

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A11: Is there a major difference between the V2 Plus and the Premium 5 for large vacuum bags?

The Project V2 Plus will handle a 4x8 flat panel with no problem if you work at a reasonable pace. The benefit of the Premium 5 is that it buys you some extra time during the glue-up process (before the bag is sealed shut). If you run into an issue while getting the project in the bag, the glue could start to set up. If that happens, 5 cfm version will pull the bag down to the project faster and reduce any chance of getting a poor bond.

The question is how much time does it buy you. There is no easy answer there since it depends on a lot of factors related to the project shape, substrate type, and veneer species. For example maple needs a very "wet" glue to make a good bond. On the other hand, walnut will bond nicely in most cases even if the glue is already starting to set up before full vacuum is achieved.

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Vacuum Bagging Questions

VB1: Since vinyl for bag making is only 54" wide, what should I do if I need a vacuum bag that is 6' wide?

Vinyl Vacuum Bag MaterialYou can make a vacuum bag of any size. I have made huge bags by making two "tubes" of vinyl and gluing them end to end. I have also glued two pieces of vinyl 54" wide by 6' long together (side by side) and then rolled the edge together to make a 4' x 6' bag. You can fuse together as much vinyl as necessary to get the size and shape you need. The HH-66 cement is very powerful stuff!

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VB2: How can I build a vacuum frame press?

It took a dozen drawings and nearly as many prototypes to finally come up with something that could be created in any woodworker's shop. The hours spent designing, building, and testing those prototypes has led to this frame press article. I hope it inspires you to build one and see how much easier vacuum pressing is with one in your shop.

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VB3: What is the difference between vinyl and polyurethane for vacuum bags?

Polyurethane vacuum bags last significantly longer than vinyl bags. With everyday use, vinyl has a tendency to develop tears and pinholes (which can be repaired). Polyurethane bags can withstand much more use and abuse because it is chemically engineered to be elastic. This elasticity is what makes it more puncture resistant than vinyl and allows it to retain its shape even when stretched to the extremes which makes it good for curved projects. Additionally, polyurethane has a much greater "memory". In other words, it goes back to its original shape after being stretched.

On the flip side, polyurethane can be considerably more expensive than vinyl and most polyurethane films can not be bonded with HH-66 cement. The good news is that VeneerSupplies.com has an affordable polyurethane material that will bond with HH-66. For more information about polyurethane vs. vinyl for vacuum bagging, click here.

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VB4: I'm on a budget and need to find a cheaper material for the vacuum bag. Any suggestions?

If you have access to an old waterbed mattress, you're in luck. The mattresses are usually made of a decent grade of vinyl. The only downfall is that most of them are not clear so seeing the panel and platens is not possible. For seasoned press users, this may not make much difference but for others, it may make things more difficult.

There have been reports that inflatable air mattresses will also work for vacuum bags but I have not tested this.

I've also received emails from users who have built a vacuum bag with PVC shower pan liner available at most home centers. It's a thick vinyl material that is gray in color and is usually sold by the linear foot. It's not really cheaper than the 30 gauge vinyl but if you have access to some scraps, it will make a nice vacuum press bag. With this material, you can cement the bag with Oatey PVC cement.

Follow-up question:
Can I use the Oatey PVC cement for making bags from vinyl material?

Nope. I've tried 3 different versions of PVC cement and none of them work.

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VB5: Can I use Space Bags and a Food Saver for veneering?

From Stuart Jackson...
I started with "Space Bags", since we had some in the house from vacation. They come in pretty big sizes and are inexpensive enough to be semi-disposable. The material is strong and they are very air-tight. I just grafted a hunk of tubing into the bag and sealed it with 5-minute epoxy. I used it with an hand- powered vacuum pump before I spent the money on a real pump. The hand pump does take a bit of work, but you can do a good job on small panels. It's a good way to give veneering a try without spending a whole lot of money or messing with making a bag from scratch.

Space Bags for Veneer?

Veneering with Space Bags?

From Bobby Tonsly...
Trying to be cheap, I decided to use one of my wife's clothing space bags for vacuum pressing a panel. The hard part was trying to get the vacuum tube to connect to the bag. I never got a connection that was completely free of leaks but I did manage to get the bag down to 21" of vacuum. The press ran almost continuously. The good news is that the panel turned out well but on the next panel, the bag developed a tear. Of course, the wife was ticked off but at least they are cheap. I ordered her a replacement bag and immediately after that, I ordered a real vacuum bag.

From Joe Hillenborough...
I placed a vacuum gauge inside of a Food Saver bag and sucked it down with the Food Saver unit. It doesn't draw enough vacuum to do veneering. I guess that why they don't call it a "Veneer Saver".

From Dave Purdy...
I used a FoodSaver to create the vacuum, not sure what the Hg was but it seemed to work quite well as it bent four 1/8" 3-ply pieces of Baltic Burch. The only bummer was getting up every 10 minutes to re-vacuum the bag.

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Vacuum Bag ClosureVB6: It's difficult to get everything into my large vacuum bag. What do you suggest?

  1. A large project going into a large bag should be the work of two people. Get a hand from a friend or spouse to help get the project loaded.
  2. Consider cutting off the seal on the far end of the bag. It is much easier for two people to load the project when one person can help pull it in from the other side. To make this work, you'll only need to purchase a second bag closure.
  3. Do not use a top platen/caul. Instead consider using breather mesh.

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VB7: What can I do to make my plastic bag closure easier to snap onto the bag?

A light coat of car wax or a wiped-on coat of silicone spray will make it easier to snap the bag closure over the vinyl or polyurethane vacuum bag. Be certain that neither of these products is accidentally applied to the inside of the bag where it could foul the work piece for finishing.

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VB8: How do I attach my existing vacuum press to the DuraMax vacuum bag?

Lock On ConnectorIf you already have a vacuum press from another manufacturer and it uses a direct tube-to-bag connection, you'll need to attach the JWW "lock-on" connector. Check the inside diameter of your existing tubing. It should be 1/4" or 3/8" inside. Using that info, you can select an appropriate barb fitting adapter for the lock-on connector. This is all you will need to convert your existing vacuum press for use with the DuraMax vacuum bags.

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VB9: Can I press multiple projects in a single vacuum bag at the same time?

Yes! You can place small projects side by side in a large vacuum bag. Use breather mesh over each project panel instead of a top platen. You can also stack identical sized projects on top of one another if you place a piece of wax paper between them. This will prevent glue squeeze-out from bonding the panels to each other. Be careful not to stack so many panels inside that the bag seams are stretched.

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VB10: What size bag can I use with my vacuum press?

Ultimately, the speed of vacuum flow from your vacuum source is what determines the maximum bag size that you should consider. If your system is underpowered, the bag will not pull down fast enough and the glue will set up before full pressure is on the veneer.

Vacuum Flow
Maximum Bag Size
For Flat Projects
Maximum Bag Size
for Curved Projects
1 CFM
4' x 4'
2' x 4'
3 CFM
4' x 8'
4' x 4'
5 CFM
4' x 15'
4' x 8'

Learn more by clicking here.

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VB11: Why does it seem like your platen/caul system is different from everyone else's?

There are several ways to build and use a platen system in a bag. I've never understood why so many people make it difficult. My method allows you to veneer both sides of the panel at the same time. If you want to use two platens as shown here, you just groove the outside faces of each and use a spacer block to fill any gaps between the two platens. But by far the easiest method, is to use breather mesh. In this case, you only need a bottom platen. It does not need grooves and you can still press both sides at the same time.

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VB12: Why do I have to leave the bag connected to the vacuum press after it pulls the full vacuum?

No matter what anyone says, a perfect seal on a vacuum bag is impossible. One could argue this until pigs fly but the bottom line is that a bag will leak.

  • Sometimes the bag closure doesn't seat perfectly across the opening and needs to be repositioned.
  • Sometimes the residual air pressure makes its way from the core of the substrate and platen components which reduces the pressure inside. This happens most often when there is a large project in the bag. You'll hear the vacuum system cycle off (if you have any auto-cycling system) and then turn on again for a few seconds. After that, it may not cycle again for several minutes or even hours.
  • After many uses some bags develop pin holes which can be hard to find. In those cases, it's best to let the vacuum press keep the bag pressure in control.

When the leak happens, you won't know it because there is no gauge on the bag. If the bag is connected to a vacuum press system, you could easily see the pressure reading by looking at the gauge. The pressure inside the vacuum system is the same amount of pressure inside the bag. If your vacuum press cycles on and off too frequently during a project, you know there is a leak and if you can fix it, great. But if you can't, at least the vacuum system will keep the bag under pressure until the panel is finished.

If you are still hell-bent on disconnecting the bag from the system, you can purchase tire stem caps from your local automotive store and attach one to your bag stem immediately after pulling the initial vacuum. But are you willing to risk a botched panel with expensive veneer?

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VB13: How is the CFM of the vacuum source related to the size of the vacuum bag?

A small vacuum pump will take a long time to pull a decent amount of vacuum on a large bag. The correlation between the vacuum source CFM (cubic feet per minute) and the bag size is simple. If the pump is too small and the bag takes too long to get adequate pressure, then the veneer glue could start to set up before the veneer is flattened by the pressure inside the bag. The result could be ripples in the cured veneer panel. To work around this, you have some options.

  • Work Fast - Once the substrate is glued up and the veneer is set onto the substrate, get the project into the bag as quickly as possible so the glue is still wet when the full vacuum is applied.
     
  • Chill Out - Try to get your shop temperature down (temporarily). Cooler temperatures slow down the setting of the glue. Don't go below 60° F or the glue may not cure at all.
     
  • Down-Size - Consider using the smallest bag possible for your project. While a large bag will work for a small project, it will also create more air space that must be evacuated.
     
  • Upgrade - Though an expensive option, you can always buy a larger/faster vacuum pump to get the bag pulled down faster.

More information about sizing your vacuum pump to the vacuum bag for your project can be found here.

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VB14: Where can I find a 4' x 8' vacuum bag with the opening on the long side of the bag?

I don't offer vacuum bags with the opening on the long side because there is no affordable way to ship an 8' bag closure. However, in theory you could make your own bag with the Build-a-Bag kit on the VeneerSupplies.com website. With it, you could seal the ends closed with HH-66 and then make your own bag closure from some wood as shown here (see method #3). Of course, such a large opening and closure could lead to a bag with more leakage than normal.

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VB 15: How can I determine if my project is too wide or tall for a vacuum bag?

There are times when you may need to put a relatively large project inside a vacuum bag. Most vacuum bag suppliers offer a 54" maximum width on their bags. You can visually determine if your project is too big for a vacuum bag by using the string theory below.

You can determine if your project will fit inside a 54" wide bag by cutting a piece of string that is 104" long (or double the width of the vacuum bag minus 4 inches). Tie the ends of the string together so you have a string loop. Find of the area of greatest girth on the project. Drape the loop over and around the project. Now simply imagine that the string is a cross-section of the bag. Use pieces of tape to hold the string against each side of the project. Do this all the way around the project so that there are no gaps. This will help you visualize the way the bag will pull onto the project. If you can apply pieces of tape to hold the string against each part of the project, then it should fit inside a vacuum bag.

If there are gaps where the string will not lay flat against the project surface because there is not enough string left, then the project is too large for the bag.

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VB 16: Will I foul up the finish if a coat of paste wax is applied to my platens?

I've never had any finishing problems caused by waxing the platens. Just be sure to let the wax dry and buff it out with a dry rag. Any sanding that you do to the panel after pressing will remove surface contaminates.

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VB 17: How do I know that I'm buying a decent vacuum bag?

There are some companies that extoll the virtues of their vacuum bags based on the width of the weld at the seams. This is a somewhat useless factor. It is the quality of the weld that matters most. A perfect weld that is 1/4" wide is better than a weak weld that is 1" wide. It is only the first sixteenth of the weld that makes it air-tight anyhow. For the record, the vacuum bags offered at VeneerSupplies.com have a perfect weld that is 5/8" wide. The weld is done with a 7,000 watt radio frequency welder.

Companies that are using "cold-weld" or "hot-air" techniques are using the wrong equipment for the welding process. That type of machinery is designed for low-cost surface bonding where the seam does not have to be air tight (such as in making tarps). The bags sold at VeneerSupplies.com are welded with radio frequency equipment because it melts the seams together under significant pressure. This method creates a seam that is stronger than the bagging material itself. It is the same method used to make drum liners for hazardous materials where a leak could be disasterous.

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Miscellaneous Questions

M1: I'd like to use a refrigerant compressor from an old air conditioner. How do I make the connection from the compressor to the first part of the vacuum press?

It can be difficult to find fittings to make that first connection. I've found two decent solutions that work on most of these pumps. First I want to remind anyone using a refrigerant compressor to please have the refrigerant professionally withdrawn from the system before you remove it from the equipment. The freon inside is horrendously harmful to our atmosphere. It's not worth the weight that will sit on your shoulders when you see how much refrigerant will come out of even the smallest system.

If the copper tubing on the refrigerant compressor is reasonably close to 1/4" outside diameter, you can make an easy connection to the first component of the vacuum press (either the reservoir or the Mac valve) by simply sliding a piece of 1/4" inside diameter vinyl vacuum tube over it. On the other end of the tube you can attached a brass barbed fitting to get to 1/4" NPT threads. If the vacuum tubing doesn't quite fit, you can heat it in hot water to make it more flexible and it will slide on easier.

If there is no way to get the vacuum tube connected directly to the copper tubing on the compressor, you can take the pump to the hardware store and find the closest matching brass component (with 1/4" NPT Refrigerant Compressorthreads) that will fit over the copper tubing and bond it on with JB Weld. Yes, this really works very nicely!

From Jim Wilson (click here for more)
"One of the obstacles I encountered was the 5/16" inlet line -- I couldn't find anything in that size locally, except compression fittings, which I wanted to avoid. Finally, I reamed a short piece of 3/8" refrigeration tubing to 5/16", soldered it to the inlet, and viola -- the inlet was resized to Air Conditioner Compressor3/8" OD. From there, the plumbing was easy."
 

Click here for James Bodnar's refrigerant compressor vacuum press article.

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M2: What kind of refrigerant compressor (from a refrigerator, freezer, etc.) works best and what brand should I look for?

Each refrigerant compressor is different. Some compressors won't be able to pull the amount of Hg you'll need to do the veneering. The brand and size of the compressor is no indication of its speed of air evacuation or its maximum vacuum level. The only way to tell is to rig a vacuum gauge to it and see.

Also, some refrigerant compressors can restart under pressure and some can not. My experience is that most will restart under pressure. Again, you'll need to test this out for your individual unit. To incorporate a refrigerant compressor into a system, you'll use the basics of the instructions found by clicking here.

The only tricky connection is getting the copper tubing on the compressor to fit to a standard NPT thread. You'll still need the vacuum reservoir, gauge, tubing, vacuum controller, and some other miscellaneous stuff too.

Information from James Redmon and Tim Cook (click here for more)
"It seems that the newer compressor units (short barrel shaped ones) do not stand up to continued use in this way. Most all of the people have reported that they run fine for about 15-20 mins then burn out. In contrast, folks that use the older "cough-drop" shaped vertical unit like the one I have seem to have no problems at all and report great results. So, my advice is to look for this specific style from a repair shop or junk yard and not waste time on the newer models."

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M3: I'd like to use a refrigerant compressor for my system. Will the lack of oil in a compressor pump cause the unit to eventually burn out?

Yes, the lack of oil may eventually wear down the pump. I used a refrigerant compressor for vacuum many times and the compressor held up fine. Maybe adding some oil from time to time would lengthen the life of the compressor. Also, be sure that you leave 8" of copper tube from the exhaust of the compressor (bent upward). This will help to keep the oil in the compressor.

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M4: Do you have any information about converting copper tubing to work with threaded fittings?

Here is an article by George Kekenes that discusses some options when working with copper tubing.

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M5: When vacuum clamping, how do I ensure a good seal on porous woods like mahogany?

There are a few options here. Test each to find which one works best for you.

  1. You can substantially reduce the effect of the wood's porosity by coating the clamping area of the block with a coat or two of shellac.
  2. Consider attaching a non-porous scrap such as HDPE to the bottom of the carving block with screws. Then clamp it to the bench with vacuum.
  3. Apply duct tape to the vacuum side surface of the project if you plan to remove it quickly immediately after clamping
  4. Apply clear packing tape which doesn't hold to the wood quite as well but is easy to remove even if you let it sit for days.

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M6: How do I connect one of the VeneerSupplies.com vacuum presses to a OneWay vacuum chuck?

A customer recently emailed me and said that the OneWay vacuum chuck has a 1/4" NPT fitting on it. He simply removed the stock fitting from the chuck and replaced it with a vacuum clamping fitting from VeneerSupplies.com. This fitting is available with a 1/4" NPT male thread. The opposite end of the fitting attaches to the lock-on connector that comes with the vacuum press.

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M7: Can I use a venturi system for vacuum chucking on a wood lathe?

A venturi based system might not be a good idea since it would cycle on and off to maintain pressure. These cycles can be problematic if the project piece is very thin at the mounting point. The fluctuations of pressure can cause the project to flex which can not only change the shape of the turned project as its is spinning on the lathe, but can also weaken the area that is attached to the chuck.

Because of this, I recommend using a vacuum source that maintains a stable level of pressure such as an electric vacuum pump. Of course, you can use a venturi for this but it will cause your air compressor to run almost non-stop. And if the air compressor cant keep up with the flow required by the venturi to maintain vacuum, then it's possible that the work piece could fly off of the chuck and wreak havoc.

For vacuum chucking with an auto-cycling vacuum press (such as the EVS system) I always recommend converting the system to run continuously instead of auto-cycling. This way the vacuum level is constant and there is no chance of the pressure dropping and letting the work piece come off.

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M8: What is your favorite kind of cookie?

I'm a big fan of brown sugar so I love chocolate chip cookies made without chocolate chips. Without the chocolate, the brown sugar taste really comes through. I enjoy this with a glass of chocolate or strawberry milk that has been in the freezer for 20 minutes before serving. Yummmmy!

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Troubleshooting

T1: I hear air leaking from the bag stem connector. What should I do?

It's commonly thought that the sound of air flow in the vicinity of the valve stem and bag connector junction is a leak. If the sound from the valve stem area is not a clear "hiss" but instead sounds more like a combination of hiss and static (as on a poorly tuned radio station), then the leak is probably coming from a hole in the bag or from the bag clamps not being tightened adequately. Actually, what you are hearing is air being removed from the bag, through the valve stem/connector and into the reservoir and pump. You can simulate this sound by turning on your system and leaving the bag end unclamped.

You can further test the connection by placing a piece of duct tape inside the bag over the bottom of the valve stem (covering the entire stem base). Then attach the connector and turn on the pump. If you do not hear any sound near the stem, then the air you had originally heard was air flow as described above and you probably have a leak in your bag.

However, if the valve stem area has a clear, unmuffled "hissing" sound, it could be caused by air leaking between the connector and the stem. In this case, be sure to apply adequate downward pressure on the connector before releasing the locking lever.

Lock On ConnectorPlease note: The vacuum connector does allow air to flow when it is not connected to the vacuum bag stem. As you can probably tell, this connector is "borrowed" from the automotive industry. The manufacturer wanted to charge three times more for a unit that would hold vacuum when disconnected. That feature isn't necessary for optimal vacuum operation and is hardly worth the expense. Additionally, allowing fresh air into the pump cleans out the air inside and prevents a buildup of airborne glue residue from occurring inside the pump cylinder.

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T2: D'oh...I punctured my vacuum bag or I have a leak somewhere. How do I fix this?

To find the leak, slide some paper inside the bag near the edges and insert your platens. Now place more paper near the valve stem and some in the vicinity of the bag closure. Close the bag and turn on the press. Allow the bag to develop some pressure. Then spray the edges of the bag with water. You should be able to see the leak if the paper becomes wet. Any leaks in the bag will show up as the water is absorbed by the paper. If not, try spraying water around the valve stem and the bag closure.

Helpful Ideas
You may find it easier to add a little food coloring to the water before spraying the bag. This will dramatically improve the visibility of the leak. I've also found that brown kraft paper shows the water results very well.

If you notice the leak while the press is running and need a quick fix, just place some clear packing tape over the hole and press it down firmly.

For a more durable patch, cut a piece of vinyl about 1" square and attach it to the outside of the bag with vinyl cement. Don't forget to prepare the patch and the exterior of the bag. Using acetone or xylene, clean the surfaces where the patch will be placed. Very fine steel wool will aid in the cleaning process, but you must be sure that no steel residue is left when you are finished. Apply the patch and press it down using a J-roller or a seam tool. Then turn off the press and allow the patch to dry over night. Patch kits are available on the VeneerSupplies.com website.

Vinyl patch kits used for repairing swimming pool liners also works well on vinyl vacuum bags.

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T3: How do I make my vacuum bag last as long as possible?

A vacuum bag will last much longer if you take good care of it. There are three important and easy to remember aspects of making a vacuum bag last for a very long time.

  1. The first is to store your vacuum bag away from UV sources such as sunlight.
  2. Make sure there are no sharp edges inside the bag. This includes the platens and the project panels.
  3. Be careful that you do not stress the seams on your vacuum bag. The seams will surely break if they are being pulled apart by vacuum. With a bag of the correct size, the seams will pull together. Imagine a very small project inside a large bag. Under pressure, you would notice that the seams actually pull together and are under virtually no stress.

Vacuum Bag Usage
The drawing at the top of this image shows a project being used in an appropriately sized vacuum bag.
The bottom drawing shows a bag which is too small for the project.

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T4: How can I test my vacuum press for leaks?

There is an easy way to test for leaks in the reservoirs and brass fittings. First, remove the vacuum line to the vacuum controller and close it off with some tape. Next, remove the bag (lock-on) connector from the vacuum line. You'll now need some soapy water. Using a paint brush, dab a little soapy water onto and area that you suspect are leaking.

If you have an air compressor, blow a little air into the vacuum tube where the bag connector was attached. If there is a leak, the soapy water will bubble up and indicate the leak. When I've been too lazy to pull out the air compressor to do this trick, I just blew into the vacuum tube using good old fashion lung pressure. Surely, it's not a pretty picture but it does work.

Be sure to clean off the soapy residue when you have finished finding the leaks. Then re-attach the vacuum controller.

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T5: My system seams to be leaking vacuum. What should I do?

To fix a leaking system, leave the system charged with vacuum and apply a small amount of silicone to each of the brass fittings and gauge where they attach to the PVC caps. If a leak does exist, the vacuum will pull the silicone into the void area causing the leak to seal itself. Also consider applying silicone to the area around the edge of the PVC caps on the pipe. This is a very common area for leaks. After you have applied the silicone, turn the system off and let the air back into the PVC pipe by opening the vacuum valve. Allow the unit to sit overnight so the silicone can cure.

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T6: I just wired my system as shown in the directions and it's not turning on. What should I do?

Try backing out the adjustment screw on the vacuum controller. Sometimes the factory sets the screw too far in for the switch to engage even at zero vacuum.

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T7: How do I reset the vacuum gauge so the needle reads zero when there is no pressure on it?

Vacuum gauges often develop internal pressure during shipment (air shipment) which must be released for the gauge to remain accurate. Simply insert a small pin under the rubber stopper on the top of the gauge. Any inside pressure will escape and the needle will reset to the zero position. If you have a glycerine filled gauge, be sure to do this while the gauge is in the upright position to prevent the loss of fluid.

Do not press to hard on the rubber stopper. If you do, you could accidentally push the stopper inside the gauge.

Update: The vacuum gauges sold at VeneerSupplies.com now includes a small pop-up button on the top of the gauge which can be used to easily reset the pressure inside.

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T8: My system is complete and it holds pressure perfectly after the pump cycles off but it takes a long time for it to shut off and I can't get it any higher than 21" of Hg. Why is that? 

There are three possible reasons for the lack of pulling power.

  1. You are at a high altitude.
  2. The pump is needs to be replaced or rebuilt.
  3. One of the connections between the pump and the check valve is leaking air.

The most likely reason is #3. You can test the pump simply by attaching the gauge directly to the pump. If it quickly pulls 25" or more, then you have a leak between the pump and the check valve.

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T9: My system was running fine for years but recently it started to cycle on and off very frequently. How do I fix this?

Debris in Check ValveCheck the check valve. The most likely culprit is debris caught under the seal inside. To fix it, simply remove the check valve from the system and blow air compressed through the check valve. Reinstall the check valve and your system should cycle perfectly. Thanks to John M. Petti for the picture and FAQ suggestion.

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T10: My glycerin-filled vacuum gauge has an air bubble in it. Is it defective?

Nope. All manufacturers of glycerine-filled gauges ship them with an air bubble inside. I have been told that this is done to keep the gauge accurate at all altitude levels and to prevent leakage during air shipping (when the boxes of gauges could be 40,000 ft in the air). A few users have reported that they were able to fill the gauge with more glycerin that they found at their local pharmacy. I don't necessarily recommend this.

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