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My sheet of plastic: How much bigger than my mold?

 
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mpmurray
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Joined: 24 Nov 2005
Posts: 11

PostPosted: Wed Dec 21, 2005 3:19 pm    Post subject: My sheet of plastic: How much bigger than my mold? Reply with quote

I'm about to try building a vacform system. Trying to decide on platen and oven size. How much of a plastic sheet margin is needed eminating out from mold?

For example, if I have a 20x20 mold - should plastic be 21x21? That's a 1-inch margin.
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crashmann
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Joined: 27 Sep 2005
Posts: 501

PostPosted: Wed Dec 21, 2005 7:27 pm    Post subject: Reply with quote

Hi Michael,

I presume you've checked out Jim Egner's abdomen pull? It barely fits on the forming platen diagonally!

There's a couple factors to consider when deciding how much margin is necessary. One primary concern is how tall is the buck you are going to be forming over? If it is more than 3 to 4 inches, you might want to give a little more margin.

Next, what do you plan on doing with the final part? The more you stretch it, the thinner the plastic will be.

Also, you're going to lose 1 & 1/2" of plastic on each side from the clamping frame. It's got to grip it somewhere Smile

Finally, you want to think about your plastic supplier. You want to maximize the number of pieces you can get from a 4' x 8' sheet. Otherwise, the supplier will charge you for the excess and just throw it away.

If you're considering a 21" x 21" platen, then you're probably looking at buying 24" x 24" pieces. No waste from a 4' x 8' sheet, and you get 8 pieces. I designed my table to accomodate 24" x 36" pieces, since you get 6 from a single sheet, with no waste (however, I find I need to remind the plastic supplier of this - They're not necessarilly the brightest bulbs on the tree Razz)

So, what are you planning on pulling with your table?

Charlie
TI-386
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mpmurray
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Joined: 24 Nov 2005
Posts: 11

PostPosted: Wed Dec 21, 2005 11:00 pm    Post subject: Reply with quote

Thanks Charlie,

I'll be doing, you'll never guess...........a guitar bowl. I haven't gotten into sci-fi as most people here seem to do. Doing some of the stormtroopers or whatever would be cool, but sure to scare my young kids!

The guitar bowl will be about 4inches deep.

Does the clamped 1-1.5" portion of plastic need to heat up also in order to be pulled onto the platen? Can I assume that the heater will do the clamped portion? I plan on having enough plastic to leave a 1.5" margin on the platen....unless someone advises otherwise.

Thanks also for your responses about your personal oven!

michael
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crashmann
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Joined: 27 Sep 2005
Posts: 501

PostPosted: Wed Dec 21, 2005 11:11 pm    Post subject: Reply with quote

You shouldn't have any trouble forming a 4" deep bowl with a 1.5" margin on the platen. A nice gentle sloping form like a bowl is ideal for vacuum forming!

The plastic clamping frame will be heated by the oven. The top of the oven is the exact size of the clamping frame, so all of the rising heat gets transferred directly to the plastic, and a little goes into the frame (that's one of the reasons we wear leather gloves when forming Smile)

Star Wars costumes are no big deal to my son, 2 1/2 years old, and daughter 9 months. Alexander is actually very proud his Dad is a storm trooper! "Stormtroopers are cool!"

Good luck with the table Michael!

Charlie
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