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Part 1
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The bag closure will be used to close the open end of the bag after you have inserted the veneer, substrate, and platens. Getting a good seal is not difficult. Read more about closures below to see which is best for you. Method 1: Tube & Sleeve or C-Channel Closure (Commercial)
For additional clamping strength, you can attach spring clamps over the C-channel. This is not necessary under normal conditions but it will provide a better seal if the bag is heavily worn. For the ultimate gripping strength, the bag may be rolled over the tube twice before the C-channel is attached. I do not recommend more than a double roll over the tube due to the difficulty of removing the closure under such clamping pressure. To remove the closure, pull the C-channel off of the PVC tube starting at one end and work toward to the opposite side until the closure is released. There is one thing to note about this type of closure. It is very difficult to get a good seal if you are using a shop-made vacuum bag in which there is an overlap of the bag material on the top or bottom of the opening. If you have built a bag and your seams are not at the edges of the bag, it's best to use method 3 below. Method 2: Tube & Sleeve or C-Channel Closure (Home-Made) Method 3: DIY Dowel Closure If there is a bow, flip the boards around until you are looking at a gap in the middle when they are held together and draw an arrow on each board facing away from the side that has the gap. Set up your router (preferably router table) with a ½" core box bit and raise the bit 1/4" high. Run both boards across this setup with the arrows pointing down (if you are using the router table). Glue a ½" dowel into one of the boards as shown above. The two boards will now mate together nicely. Allow the dowel to dry before continuing.
Then place clamps along the length of the closure every 6 to 8 inches. Be sure to place a clamp over the seam overlap on the vacuum bag. This is where most leaks occur. From Farrell Boris of Old Westbury, New York:
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Find a
hardwood board that is 5" wide, ¾" thick, and 30" long
(or 3" longer than your bag's width) and rip it in half. Now hold
the two pieces together (as if you were going to glue the ripped
edge back together). See if there is a slight bow. Sometimes wood
will do this and if it does, this time it will be an advantage. If not,
don't worry.
This
is your bag end closure. I prefer to use standard wood clamps starting
at one end. Then place another clamp at the opposite end. Just before
tightening this second clamp, use your index finger to pull the vinyl
bag away from the first clamp. This keeps the vinyl flat under the bag
closure. 
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