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positive pressure membrane thermoforming
01-27-2013, 05:03 AM
Post: #1
positive pressure membrane thermoforming
Has anyone ever tried making a pressurized membrane press? I saw an industrial press that applies pressure on top of the membrane rather than creating a vacuum below it and I have an idea of how to make one. I wanted to try this method because I have an air compressor and it seams like I would be able to apply more pressure than vacuum can and get more definition. What are your thoughts on this?
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Old Faithful Holsters
01-27-2013, 07:28 AM (This post was last modified: 01-27-2013 07:54 AM by Sam.)
Post: #2
RE: positive pressure membrane thermoforming
My first thought would be to study all the Kydex Technical Briefs when it comes to thermoforming. There are about 12 technical briefs on forming Kydex. Here is the link - http://www.kydex.com/technical-data/tech...riefs.aspx

I've seriously considered purchasing a thermoforming machine for Kydex, but it's difficult because most sellers only work with thin plastic sheets on their machines. Before purchasing one, I would have to the thermoforming machine with various sheets of Kydex in different thicknesses.

I've also considered a thermoforming machine as well, but it's too time consuming for in order to see if it works or not.
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01-27-2013, 08:43 AM
Post: #3
RE: positive pressure membrane thermoforming
I was thinking more along the lines of making something similar to what most people I've seen do with diy membrane vacuum forming except eliminate the vacuum and creating a pressure chamber having the membrane as the bottom wall of the chamber. Then you would clamp this over your gun and kydex and pressurize the chamber.

Idk if I am clear as to what I am planning but I was hoping to get some thoughts on using this method.
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01-27-2013, 08:49 AM
Post: #4
RE: positive pressure membrane thermoforming
Thermoforming is not exclusive with vacuum forming, but also includes pressure forming.

In the various Kydex technical briefs there is a section dedicated to pressure forming.
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01-27-2013, 12:12 PM
Post: #5
RE: positive pressure membrane thermoforming
(01-27-2013 05:03 AM)squeakh Wrote:  Has anyone ever tried making a pressurized membrane press? I saw an industrial press that applies pressure on top of the membrane rather than creating a vacuum below it and I have an idea of how to make one. I wanted to try this method because I have an air compressor and it seams like I would be able to apply more pressure than vacuum can and get more definition. What are your thoughts on this?

Yes, you can get 10 times the pressure with a $30 compressor than you can with an expensive, leak free, vacuum system.

Before you start on your pressurized membrane adventure, you should develop a through understanding of the physics involved and then sit down with a calculator and crunch numbers.

Here's some free advise, which is worth what you're paying for it. It's much easier to kill yourself with a pressure system than it is with a vacuum system.
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01-27-2013, 12:27 PM
Post: #6
RE: positive pressure membrane thermoforming
I understand your point about safety. I will probably use a portable tire pump for start to test the waters with the amount of pressure, but I am also building it in a cad program to simulate the shear and normal stresses applied within the materials under pressure to determine a safe max pressure and only pressure up to half the max.

P.S. I'm a mechanical engineering student so I understand a little about all this but I have a lot to learn still.
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01-27-2013, 01:51 PM
Post: #7
RE: positive pressure membrane thermoforming
my understanding is that even with the best vacuum system you are only getting the equivalent pressure of 1 atmosphere which is about 14.7 psi., so anything over that would be more than a vacuum system so that is why I wanted to try this method.
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Old Faithful Holsters
01-30-2013, 06:11 AM
Post: #8
RE: positive pressure membrane thermoforming
You don't need air to have a positive pressure forming system. Anyone who is using foam is exerting positive pressure to make the mold. I played around with a positive pressure air system a while back and quickly found out that for the membrane to be thick enough to hold pressure it has to be too thick to get good definition. in addition, you want to make sure that your pressure vessel can withstand whatever pressure you are want to maintain. An altogether costly and unfruitful endeavor in my humble opinion given there are much cheaper and safer methods of accomplishing the same results.
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01-30-2013, 07:29 AM
Post: #9
RE: positive pressure membrane thermoforming
I have no experience with positive pressure molding systems, other than reading the technical briefs and contemplating the idea. It seems from your previous comments, would this be for a college project? If you're set on a positive pressure mold, then would a simpler shape like a magazine holder, or a belt clip attachment be better for a positive pressure mold?
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01-30-2013, 10:45 AM
Post: #10
RE: positive pressure membrane thermoforming
I was planning on doing this for personal reasons rather than a college project. From what I have available to me without going "shopping" it would be cheaper to do a vacuum press but I dont have a vacuum pump. I only have a large shop vac.

Which would be better for hybrid holsters, using a single sided foam press or a membrane vacuum method with a shop vac? As a college student I cant afford a vacuum pump setup right now so I am trying to find the best affordable method.
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