Saturday, August 21, 2010

Super Suction!

So a while ago I decided to try using a vacuum bag press to form leather cases.  I'd seen the vacuum bag presses used for veneering and making skateboards and figured the principle would transfer well to leather forming.  So far it seems like I was right.

I bought a vacuum press kit marketed by Roarockit for making skateboards.  It cost about $50, and it came with a hand pump, some breather mesh (helps get all the air out) and some awful sticky mastic (tar) tape for sealing up the open end of the bag.  It worked pretty well, and in fact I used it to form the magazine holster featured in Manly Sewing Project #2.  But pretty soon I learned that I hate mastic tape and manual pumping sucks.

As luck would have it, I managed to get my hands on a gently used laboratory grade two-stage rotary vane vacuum pump.  It would have cost me about $3000 new, but I got it for free since it was headed for the scrap pile merely because the lab didn't need it any longer and had no other avenue for disposing of it.  It works flawlessly and is actually way more pump than I need since it will draw a high vacuum at a rate of 12 cubic feet per minute (I only need about 2 cu.ft/min).  Since it weighs about 60 lb I'll be building a rolling cart for it eventually.

I also went to and ordered a valve kit, hose, brass valve clamp, and bag closure.  I installed a second valve on my vacuum bag and got rid of the mastic tape.  Now I can use my vacuum pump and the bag closure seals really well without the sticky mess.

Here it is:

The plywood board in the bag is for when you want to press from the top only rather than top and bottom.  The black mesh stuff is also placed in the bag either with the article inside it or else with the mesh next to the article, to help provide small passages for all the air to get sucked out.

Here's the valve I installed, and the valve stem clamp on the end of the hose.

This is the original valve that works with the hand pump (not shown).

This is the marvelous clip for the bag end.  Basically the bag gets sandwiched between the white and blue pieces.  Works great.

Obviously there's no leather in the bag in this shot, but you can see how the breather mesh works and how tightly the vinyl bag forms to the pistol.

Here the mesh is placed next to the pistol instead.  This method still allows you to get all the air out, but doesn't leave a funny mesh pattern on your leather.

I've made a few cases in this press already and it works great.  I used to have to prepare my leather (soak it and then mostly dry it until it's damp and stretchy) and stretch and form it by hand.  It took a long time and almost never looked quite right, especially for complex shapes.  Now it's just 10-20 minutes in the press and I can pull it out and let it dry.  I can also sharpen creases and lines by hand a little more if I want before drying.

Eventually I'll probably make my own bag out of polyurethane sheeting because it's stretchier and should allow the press to mold even tighter, but this works for now.  I'd also make it more squarish rather than long like a skateboard.

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