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Step 3Making a bag press.
A bag press is basically a giant ziploc bag with a connector where you can attach a vacuum. A bag press works on the principle that nature resists a vacuum therefore if you suck all the air of a container it will squeeze in on itself therefore creating a press that is excellent for bending things onto a mold.
Take two 3 foot x 4 1/2 foot sheets of vinyl plastic (fig.3a)and apply a liberal coat of contact cement glue on both sheets along the two long edges and one of the short ends.(fig.3b) Allow the glue to dry for 45 minutes. Carefully, start with the back edge and press glued edges together being careful not to create ripples. Once the back edge is pressed, work up the sides to the open end of the bag. Once all surfaces are contacted apply force to tops of glued areas by rubbing with a spoon or a rolling pin. You can then add extra reinforcement by folding strips of duct tape over the edges to strengthen the seal and plug any leaks.(fig.3c)
Now, you need something that will suck the air out of the bag. I used a vacuum cleaner with a hose attachment which worked fairly well. You also need to figure out some way of attaching the vacuum to the bag. I used a plastic tube that hooked up with the hose attachment.
Create a hole smaller than your connector pipe (but large enough that it can be forced through) in the middle of the top layer of the vinyl sheet.(fig.3d) Then force the pipe through from the inside of the bag out so that it is almost all the way though.(fig.3e) Mix up half a table spoon of 5-minute epoxy and place liberal amounts of the glue in the trench between the plastic pipe and the vinyl from inside the bag.(fig.3f)
Now you need to create a giant zipper to seal the bag. To do this take a plastic 3/4 inch conduit pipe(fig.3g) and a dowel that fits not quite snuggly inside it. Cut the pipe and dowel so they are a little longer than the opening of the bag. Then cut a strip out of the conduit length wise(fig.3h) so the cross section of the pipe is a "C" shape.(fig.3i) The cut can be made with a sharp exacto knife or I used a mini circular blade in my Foredom. To make sure the cuts are straight it helps to first use a marker to draw guide lines of where you want to cut. How the seal (zipper) works is that the "C" shaped tube goes on one side of the opening of the bag and the dowel goes on the other side. Then the sandwich is squeezed together by hitting the dowel with the rubber mallet, forcing the dowel and vinyl inside the c-tube creating an air tight seal.(fig.3j) More or less material may need to be removed from the "C" cross section if the dowel will not snap into place. I suggest making a small test zipper with extra dowel and conduit pipe to determine the exact shape needed before making the real one.
Take two 3 foot x 4 1/2 foot sheets of vinyl plastic (fig.3a)and apply a liberal coat of contact cement glue on both sheets along the two long edges and one of the short ends.(fig.3b) Allow the glue to dry for 45 minutes. Carefully, start with the back edge and press glued edges together being careful not to create ripples. Once the back edge is pressed, work up the sides to the open end of the bag. Once all surfaces are contacted apply force to tops of glued areas by rubbing with a spoon or a rolling pin. You can then add extra reinforcement by folding strips of duct tape over the edges to strengthen the seal and plug any leaks.(fig.3c)
Now, you need something that will suck the air out of the bag. I used a vacuum cleaner with a hose attachment which worked fairly well. You also need to figure out some way of attaching the vacuum to the bag. I used a plastic tube that hooked up with the hose attachment.
Create a hole smaller than your connector pipe (but large enough that it can be forced through) in the middle of the top layer of the vinyl sheet.(fig.3d) Then force the pipe through from the inside of the bag out so that it is almost all the way though.(fig.3e) Mix up half a table spoon of 5-minute epoxy and place liberal amounts of the glue in the trench between the plastic pipe and the vinyl from inside the bag.(fig.3f)
Now you need to create a giant zipper to seal the bag. To do this take a plastic 3/4 inch conduit pipe(fig.3g) and a dowel that fits not quite snuggly inside it. Cut the pipe and dowel so they are a little longer than the opening of the bag. Then cut a strip out of the conduit length wise(fig.3h) so the cross section of the pipe is a "C" shape.(fig.3i) The cut can be made with a sharp exacto knife or I used a mini circular blade in my Foredom. To make sure the cuts are straight it helps to first use a marker to draw guide lines of where you want to cut. How the seal (zipper) works is that the "C" shaped tube goes on one side of the opening of the bag and the dowel goes on the other side. Then the sandwich is squeezed together by hitting the dowel with the rubber mallet, forcing the dowel and vinyl inside the c-tube creating an air tight seal.(fig.3j) More or less material may need to be removed from the "C" cross section if the dowel will not snap into place. I suggest making a small test zipper with extra dowel and conduit pipe to determine the exact shape needed before making the real one.
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Jan 4, 2009. 11:09 AMgarethfarfan
says:
I don't get it. Is there not some type of valve that maintains the vacuum?
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Jul 15, 2009. 12:23 PMtdayt
says:
I have the same question. I don't know if he leaves the vacuum on for the whole time or if he has some type of seal for the valve. I wonder if you could just turn off the vacuum and quickly cover the valve with duct tape before it refills with air. Hmmmm.
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4
Jul 3, 2010. 4:35 PMlerickson
says:
I was wondering the same thing how did your guys turn out?
Reply
Apr 11, 2012. 3:06 PM___
says:
He prob just leaves the vacuum on the entire time
Reply
Jun 30, 2007. 2:32 AMfreewheeler
says:
quite an innovative seal design
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