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Unread 02-08-2013, 04:21 PM   #1
Starlit Rose
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Vacuum forming and non-flat surfaces

This is more of a curious question than anything, but what happens when you try to vacuum form over an object that does not lay flat against the surface of the vacuum forming machine top? All the vacuum forming examples I've seen use objects with flat bottoms, so I'm curious to know what happens with the plastic when something does not lay flat.

I ask because I eventually plan to vacuum form this shape (the bigger one) with clear plastic:
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As you can see, it doesn't lay flat. I'd have to attach some kind of bottom to it that would sort of fill the gaps between it and the top of the machine.

I'm just trying to learn the limits of what all I can do with vacuum forming. Someone's knowledge would be appreciated!
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Unread 02-08-2013, 05:01 PM   #2
verdatum
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When the piece doesn't lay flat, the plastic attempts to envelop it. In extreme cases, there isn't enough of a pressure differential to stretch the plastic all the way around the piece, so it just stretches as far as it can and then the plastic starts to cool.

If it can stretch sufficiently, you end up with your buck firmly locked inside the plastic sheet, and you will have to slice the plastic to get it out. This is also true for any major undercuts in the piece, whether on the bottom or not.

If you are just trying to replicate the top side of the piece, you can simply fill in the underside with clay. If you want the bottom edge of your piece to be well defined, you just fill it in with clay going inward by a fraction of an inch such that you define a lip.
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Unread 02-08-2013, 05:16 PM   #3
Starlit Rose
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Quote:
Originally Posted by verdatum View Post
When the piece doesn't lay flat, the plastic attempts to envelop it. In extreme cases, there isn't enough of a pressure differential to stretch the plastic all the way around the piece, so it just stretches as far as it can and then the plastic starts to cool.

If it can stretch sufficiently, you end up with your buck firmly locked inside the plastic sheet, and you will have to slice the plastic to get it out. This is also true for any major undercuts in the piece, whether on the bottom or not.

If you are just trying to replicate the top side of the piece, you can simply fill in the underside with clay. If you want the bottom edge of your piece to be well defined, you just fill it in with clay going inward by a fraction of an inch such that you define a lip.
Yeah, that's what I planned to do for this - fill it out the bottom of it with clay or something. I was just curious to know just how much it would start to envelop the underside if there was one. Thanks for answering my question! I'll keep your suggestion in mind for getting a nice, rounded edge.
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Unread 02-10-2013, 02:23 PM   #4
underdog1425
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fill it with great stuff expanding foam then when done just dissolve it with acetone
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