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The Official Website of this Non-Professional Woodworker ™ |
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Part 1
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The process of making an airtight bag had eluded me for many months. Time after time, I would make a decent sized bag and take all the necessary steps to prepare and seal it, only to notice a tiny leak somewhere. It was nothing but pure accident that led me to discover a solution that would seal the leaks on even my oldest bags. The secret? Well...read on. The vinyl can be purchased at any place that makes boat covers or canvas awnings. Some fabric stores also offer it. If you have a difficult time finding vinyl for the bags, it can be purchasd it at VeneerSupplies.com. There are a few different thicknesses available in vinyl membrane sheeting. The most common are 20 gauge and 30 gauge. Either will work with similar results but the 30 mil will last longer. Polyurethane bagging material is also available. If you are building your first vacuum bag, consider building it from vinyl. Though the polyurethane will last longer, it is more expensive and can be more difficult to work with when building a custom-size bag. The time involved in building a vacuum bag offsets any savings over buying one pre-made for most people. The instructions below will work with vinyl or polyurethane.
Small or Narrow Vacuum Bags For this example, we will be making a bag that is an 18" x 54" rectangle. Cut a piece of vinyl that is 36" in length. The standard width on almost all vinyl sheeting is 54". Bring the two 54" sides together. Remember, the bag should be about 18" by 54" not 36" X 27". The first two ends should come together so that the result forms a large tube. You do not want the shape to resemble a drop of water (see pictures).
Using acetone or xylene, clean the surfaces where they will overlap (about 2 inches will do). While the xylene is drying, mentally prepare yourself for the next steps. Try to envision the area where the two ends will overlap. Two inches of overlap will make a nice joint. You will want to apply more cement at the inside and outside edge where the overlap stops. You may find it easier to roll the bag inside-out to get to the inside seam flap. For vinyl, let this dry for an hour or so. For polyurethane, wait 24 hours before continuing and use two flat boards and some spring clamps to keep the seam tight while curing. Next, you need to seal one edge of the two that remain in order to make a bag. Lay the bag down so that the first seam that you made (already cemented in place) is centered at the bottom of the bag. Clean the surfaces of the mating edges (at one end of the bag) with acetone or xylene, and proceed with cementing as you did for the first seam. Be sure to use the seam tool to firmly press the corners tight. At the bag end, you won't be able to make the "tube" shape so it will more resemble the tear drop shape this time. If you have an extra piece of vinyl, it would be well-suited to reinforce the end seam. Cut a piece 3" wide that is as long as the bag is wide. Clean the strip with xylene, and press it evenly over the end seam so that equal amounts of vinyl are over each side of the bag. The results of the cementing may not make a 100% air tight seal. Don't worry about that yet. The secret will be revealed soon.
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