Why does half of my kydex always shrink?

[Grease]

I'm baffled by the behavior of my kydex. I put 2 basically identical pieces into an evenly heated oven for just a few minutes, and when I pull them out I always end up with one piece that has shrunk in some weird way.

I keep wasting big chunks of kydex, because I either have to use extra big pieces to ensure that the shrunken one will still fit the knife, or I throw away a piece that is now too small and warped to be useful.

It's always one piece, not both. They are both cut from the same sheet of kydex, they both sit the same distance from the heat source in the oven, and yet one reacts very differently from the other.... Why?

 

[sonil]

I'm baffled by the behavior of my kydex. I put 2 basically identical pieces into an evenly heated oven for just a few minutes, and when I pull them out I always end up with one piece that has shrunk in some weird way.

I keep wasting big chunks of kydex, because I either have to use extra big pieces to ensure that the shrunken one will still fit the knife, or I throw away a piece that is now too small and warped to be useful.

It's always one piece, not both. They are both cut from the same sheet of kydex, they both sit the same distance from the heat source in the oven, and yet one reacts very differently from the other.... Why?

Kydex does shrink...and elongates too, some pieces shrink more than others, if it warps too, you temp is high,and you left it too long in the oven, lower your temp,
read this, it will help you understand few things:

http://www.shopdiyholster.com/blog/thermoform-sheet-and-the-line-of-extrusion-/

 

[Kiah]

What Sonil said (and the link). I'm guessing even though you're cutting from the same piece of material that you're cutting in different directions. Don't do that. Mind the extrusion lines and you'll always have a good idea of what a piece is gonna do.

 

[BlueFalcon]

I've played extensively with Kydex and here is my pro tip / two cents worth, if you are still looking for answers.

Use a convection oven. Start at 200 degrees and bring it up 25 degrees at a time and based on the kydex thickness, will determine the end temp. Use a temp gun to check the temperature . Take the kydex out when it reaches your target temp immediately.

The main problem I would say you are having is heating the Kydex too fast, and too hot. Direct heat will warp Kydex i.e (convection is better), and heating too fast will shrink, gloss and possibly melt it. Heating it for too long at 300 degrees+ will cause it to warp shrink and change color as well. Be diligent check the temperature consistently and you should be fine.
Doing it this way will completely eliminate warp, it will almost completely mitigate shrinkage, and will never gloss or melt. Good luck bud .