[kaseencook]

I have made a vacuum forming table, and it works well, but with the PVC (0.38mm, clear rigid sheet) it cools too quickly and only forms the top half of the master and is room temp within seconds.

The recommended forming temperature was 130C. There was sag in the PVC before I moulded, but perhaps not enough. I also did some more research on the temp ranges for PVC, and found that 115-130C was elastic, 160C plastic and at 180C degrades. Do I want the PVC to be in a "plastic" state for forming or elastic state? I am thinking I need to raise the heat to 160? But I of course do not want to find out the hard way that it might fall apart or release chemicals at the plastic stage - so I thought I would ask.

Also, has anyone tried to vacuum form flexible Vinyl? I think it would make really great flexible moulds, but I am not sure if it is safe to heat and will melt or form. I imagine would need the same temps as rigid PVC.

Thanks for your help!

[jdougn]

What style table did you build? What type of vacuum system are you using?

On the plastic, try going hotter. I use ABS so my experience is different, but it seems like a lot of this process is determined through experimenting with the exact setup and specific plastic. The ABS doesn't reflect a temperature to go by with a non-contact laser thermometer so it's more important to go by sag and results. The same is probably true for what you're doing. With my setup (oven on top) I left plastic at the oven until it started to degrade & melt just to see what that looked like. Helped me understand what the limit was for sag and temperature.
hth, DougN

[teamtexas]

I also did some vacumn forming with an oven on top homemade former. I used .125 ABS and .250 ABS with a texture on one side. ( like the stuff they use to make car door panels). As I recall I waited through the initial sag and as the plastic started to tighten again I pulled the vacumn, moved the oven out of the way and cooled it with water before I lost my reserve of vacumn. I never check the temp on the ABS, but you could use light pressure with a screwdriver and it would leave an indention on the plastic.

Dan

[One of Many]

The forming characteristics sound very similar to polycarbonate. Run it hot to get it to form and get it off the die with a rapid cooling time before it shrinks tight.

Pay careful attention to the heating area verses the forming area. Any shadowing by the frame will prevent or rob the outer edges of forming tempurature. Sag can move the sheet further away or closer to the heat source, which also affects the forming ability.

Other than hard limits to burning. Learning to read the material in a given situation, will gain you more capability than by the book specifications.

DC

[kaseencook]

Thanks for the replies!

I have been doing a lot more experimenting since my first post, and yup, the temp was not hot enough and I didn't let it sag enough. I think my oven is cooler than the dial says. But, I am starting to learn the best sag depth for different types of pulls to avoid webbing but still getting enough plasticity. Practice, practice, practice!

Thanks!