Tips for forming acrylic

[Kottwitz-Graphics]

I have a friend that is trying to form Chemcast acrylic (.220) over a plug mold to make a replacement minitruck part (targa top roof).

He is having an issue with the acrylic bubbling before it forms. Is he heating it too fast or too close to the heaters or should he dry the sheet before attempting to form. He was told that he had to dry the sheets before attempting to form, but I've never heard that, but I've very limited experience with forming faces.

 

[rjssigns]

I have limited experience and its been years so bear with me. I'm assuming he is vacuum forming so let's start there.
When clamped in the forming rig the heater should be about 2" from the surface.
If you are getting bubbles the heat may be too high/material too close. Can't remember the exact temp but when forming 0.040" it took about 4 or 5 minutes to get ready.
Ready is when the clamped material starts to sag in the center. Not very scientific but it works every time.
The rest of the process is dependent on the vac form/strength of vacuum. (folks actually do this with a shop vac)
Done correctly you can tell right away if you made a good part.

An important item is to make sure you have at least 5 degrees of draft on the form. No draft and you'll never remove the part in one piece.