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.
- Do you want a system that cycles on/off automatically or one that runs continuously?
- If you want your vacuum press to cycle on/off, do you want it to be powered by electricity or by compressed air?
- What is the maximum project size you estimate that you will want to put in a vacuum bag?
- 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 "pounds per square foot" of total pressure can be calculated by multiplying the vacuum (in Hg) and dividing by 2; 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' x 2', the calculation is as follows:
(23 ÷ 2) x (12 x 24) = 3,312 total pounds of force
For more information, see this chart.
Another way to get a rough estimate of "pressure" on the platen is to simply multiply the vacuum level by 70 and then multiply that number by the number of square feet on the platen. Let's us a vacuum pump pulling 21" Hg on a 4' x 4' platen as an example:
(70 x 21) x (4 x 4) = 23,520 total pounds of force
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G4: Why is the Excel 5™ system faster than the Project: EVS-2™ 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-2 system using the same Gast vacuum pump. There are two reasons for this difference.
- The vacuum reservoirs used on the EVS-2 kit are added air space that must be vacuumed in addition to the vacuum bag itself.
- The Excel system is very efficient with air flow and has less restricting parts than the EVS-2 system such as the Mac valve and check valve.
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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™
- 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 |
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 |
| 4' x 9' to 6' x 15' vacuum bags |
5 CFM for flat panels |
9+ CFM for curved panels |
| Vacuum clamping |
1 CFM for non-porous materials |
3+ CFM for porous materials |
| Vacuum chucking on a lathe |
1 CFM for very small projects |
5 CFM for medium projects |
More information about this topic can be found at this link.
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 G8: Will quick-connect fittings for compressed air work with vacuum?
Unfortunately, most quick-connect fittings for compressed air will not work with vacuum. There are 4 common types of these fittings for compressed air and I've tried each. I also tried different brands of the same types of connectors. Some held vacuum if the hose and coupling was held perfectly inline with the coupler but leaked as soon as the hose was moved off-center. Others held vacuum during some of the tests and then leaked during subsequent testing.
I've only found one quick-connect system that works perfectly for vacuum and I now offer it at VeneerSupplies.com for a reasonable price.
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G9: Is it safe to use PVC for the vacuum reservoirs? What about ABS pipe?
 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.
ABS Pipe
After a phone conversation with a tech a Uni-Bell, I can not recommend ABS pipe for the vacuum reservoirs. 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.
 About 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?
The most important thing to know is that a larger reservoir does not increase the speed at which the system can reach full vacuum. If you charge the reservoirs with vacuum before opening the line to the vacuum bag, you will only increase some of the initial vacuum draw on the project however, the total time to reach full vacuum will be no different than a system without a larger (or additional) reservoir. The only exception to this is when the project and vacuum bag are very small and the additional reservoir is extremely large. I've never seen a system capable of using only its pre-charged vacuum to bring any size bag to full vacuum.
Keep in mind that if you do not charge the reservoir system with vacuum before starting flow to the project, then a larger (or additional) reservoir will increase the amount of time to reach full vacuum.
The only possible benefit to a larger reservoir is that it 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 perceived 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 controllers I offer should not be used without a vacuum reservoir. The vacuum reservoir serves as a storage buffer and 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 both kits and pre-assembled systems achieve similar results, there are several inherent quality differences between them. I've seen many of the low-tech vacuum systems in operation and I'm sure they work well but their systems consist of a cheap vacuum pump and shoddy accessories that often prove less than durable. The vacuum pumps offered at VeneerSupplies.com are thoroughly tested to the extent at which it borders on "torture". I've even run pumps at full vacuum for two days in my car in the hot summer sun here in Maryland, and I'm convinced these are some of the best vacuum pumps available.
Additionally, the vacuum press parts at VeneerSupplies.com are all nonproprietary so you can add and replace parts if needed. You can also modify the unit to do other things. The kits are easily adaptable for use with vacuum clamping and templating. The kit design allows you to attach additional bags with simple T-fittings found at the hardware store if needed.
| The VS vacuum press kits require a bit of your time to assemble, but in exchange you get heavy duty components adapted from other industries (at industrial level specs); not cheap parts that were designed to fail so a huge corporation can maintain a healthy profit. A good example of this is the VS vacuum gauge. On other systems, a plastic gauge is used that has nothing to prevent needle fluttering. This movement makes it almost impossible to accurately read the gauge. The gauge used on VS vacuum press kits is stainless steel and it has a built-in damper that dramatically reduces needle fluttering. |
Needle Flutter |
And unlike the bare-bones kits offered elsewhere, our Excel™ vacuum press kits have a fully adjustable vacuum range for delicate projects. You can dial it in for any pressure from 560 to 1700 lbs of pressure per square foot.
The truth is that we (my wife and I) don't have the "overhead" as other companies. We ship 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 1 ™ Vacuum Press Kit |
. |
Generic Vacuum Press Kit |
| Pump |
1.4 CFM |
|
.8 to 1.0 CFM (typically) |
| Tubing |
1/2" O.D. double-braid reinforced vinyl |
|
5/16" O.D. vinyl |
| Filter |
High-efficiency, high-flow |
|
None (!) |
| Adjustable |
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 |
|
Plastic |
| Bag Connection |
Brass lock-on connector |
|
Vinyl friction fit |
| Clamping Kit |
Available and inexpensive |
|
Not available |
| Retail Price |
less than $300 |
|
$479.00 (but often includes a bag) |
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.
 Veneering: 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.
 Woodworker'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: V4 or EVS-2 system, you can easily wire in a switch to convert it to run continuously.
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G16: Are there two different types of lock-on connectors on the VeneerSupplies.com website?
Yes! A new lock-on connector was introduced in February of 2020 that is a nice improvement over the previous version. More information can be found on the product page.
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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, 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: How does altitude affect a vacuum press?
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 amount of vacuum would be fine for 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 just a matter of personal preference.
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G22: Do the PVC reservoirs shorten the amount of time it takes to evacuate a vacuum bag?
If you precharge the reservoirs with vacuum (by closing the vacuum valve), then the reservoirs have no effect on the amount of time that it takes to draw the air out of a vacuum bag. The purpose of the reservoirs is simply to minimize the frequency of the on/off cycling of the vacuum pump.
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G23: Can I use a vacuum press for clamping boards together face to face?
At sea level, a typical vacuum press can put down the equivalent of 1,750 lbs of pressure per square foot. If the boards are flat, then this is generally considered more than adequate for a project where two sheet materials such as plywood or MDF are being glued together face to face. This also is true for gluing solid wood boards together.
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Any 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 
The 
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.
The second most most common cause of the appearance of a defective vacuum controller occurs when the wires are attached to the wrong terminals on the unit. The "common" terminal is hidden under the removable plastic shroud on the vacuum controller. When it is hidden, user mistakenly attaches the two wires to the "normally closed" and "normally open terminals". The correct wiring should be to the common and normal closed terminal. Be sure to remove the plastic shroud and apply the wires to the correct terminals. 