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qcumber · Joined: 09 Jan 2010 Posts: 3

Hi All. Tonight I attempted my first vacuum forming project. My goal was to create a case that will hold single blister packs of historical and fantasy miniatures. Here are a few pictures of my mold, as well as the final product with all its problems:

http://www.flickr.com/photos/91086021@N00/4260776649/
http://www.flickr.com/photos/91086021@N00/4260749179/
http://www.flickr.com/photos/91086021@N00/4261503162/
http://www.flickr.com/photos/91086021@N00/4261503240/

There are a number of problems, but the main one is the "X" that has formed at the corners of the bump-out, due to the plastic folding over on itself slightly. I am not quite sure what has caused this. I am using 1/32" PTEG and the oven was set to 300 degrees. The vacuum is a small shop vac. An idea I had was that a stronger vacuum and lower temperature might help. Does anybody have any thoughts that might point me in the right direction? Thanks in advance.

ahillworks · Master Joined: 18 Nov 2007 Posts: 308 Location: Orlando FL

The X is caused by a few things. It may be caused by the plastic being to hot and may have stretched (sagged) to much when it was in the oven. I got that allot when I was making my molds. I learned with PETG it does not need to sag unless the mold is very tall. In your case it is very small so it only needs to be hot enough to just form fast.

Some times what can cause it is spacing is not far enough from each peace. In your case one is on top of the other so that is not the issue. The issue may be it needs a wedge.... Something to prevent it from just str8 lines. I do not have a picture other wise I would show you. Simple way to explain is draw a square. Then below that square draw angels like ramps below each corner. This keeps the plastic from pinching.

Another thing could be to much pull from the air. In other words may be some trial and error before you get it right. Took me 6 tries with PETG because of the shape I was working with.

Now after all that has been said what I suggest is seeing if getting the plastic out before it sags see if this works....... Then go from there. PETG stretches its the coolest thing so do not let the plastic sag if you can.

Another suggestion is to make a mold the opposite way calling it a negative mold which means the plastic is sucked into the mold it self. This works almost every time for detail molds.

These are some things to keep in mind and try. Good luck by the way.

Anthony H.
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qcumber · Joined: 09 Jan 2010 Posts: 3

Great, thanks Anthony. I'll experiment with the temperature first. There was about an inch of sag on my 12" x 12" piece, so it sounds like that is too much. I had a few other runs and one of them there was no sag but it was too stiff to form and the other other 2 runs there was even more sag and there were folds all over the place. At least I seem to be narrowing in on it. I'll try the ramp, too, to see what effect that has. I think maybe the plastic I am using is too thick for what I want to accomplish so I don't mind using a bunch of it to experiment and learn. Thanks for your help.

ahillworks · Master Joined: 18 Nov 2007 Posts: 308 Location: Orlando FL

Yeah you could go one size down. What are we using to pull this with? Examples are pump, shop vac ect.... Also you should not need any sag at all.... the plastic does stretch to form the mold but must be pulled with a good air source.

In each corner of the mold you have for the lifted square I would drill a small hole where air can get sucked threw this may help pull tight and not loose like it is now.

Make sure you are using like window screen mesh below the mold this will ensure air flow to the holes of the mold.

Hope this all helps. I was up to late last night to type or think lol sorry.
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qcumber · Joined: 09 Jan 2010 Posts: 3

Hi, thanks for that idea. I actually had already drilled some holes under that part of the mold, more in the middle though and not on the corners like you have sugested. I'll give that a try. I am using a small 1 hp shop vac, with the filter still on (i probably should have removed it since it does nothing but reduce the suction). My vacuum table has an aluminum top with a lot of holes drilled in it, so it acts like a screen.

I am going to try again this evening. My wife is baking a cake in the oven this afternoon and that unfortunately has priority. It looks like a tasty cake, though.

d8^)