Vacuforming: when's the plastic hot enough? + misc.

[Dukat, S.G.]

All,

I'd like to sincerely apologize in advance if this question's in the wrong forum and/or if I'm missing a sticky somewhere. I searched the site for "vacuform" and turned up zip.

In any case ...

I built a "vacuform table" very much like this bugger:

http://www.studiocreations.com/howto/va ... table.html

I put my styrene in a secure frame and heat it in an oven at 450 deg. Farenheit. After 3 minutes or so, the plastic started to droop ~3-4", at which time I whipped it as quickly as I could onto the table.

Apparently that wasn't enough, because the results have been ... poor, to say the least.

I realize it's a trial-and-error shindig, but how much "droopage" should I expect before I yank the styrene from the oven?

Note: I realize this is probably dependent on the styrene's thickness. The sheets I'm using are ~6" squares; and up 'til now, I've used relatively thin sheets (not Evergreen's thickest fare, but only a step or two removed).

Any pointers or other troubleshooting ideas are most welcome.

[davidlgreen]

just started to give vacuum forming a go this weekend. poor first results
believe as you prastic no hot enough. did find some websites that seemed helpful will post url's when i find them again.

[Lt. Z0mBe]

Thanks for that! Excellent, simple design!

Kenny

[Kenny]

I'm a little out of practice but haven't had any problems with getting the detail my self in vacforming.

Looking at the small pictures it looks like the sucking might be part of the problem as one hole will make air voids.

This is my home made box

As for the temperature I wait till the styrene near the edges droops as well (I set my oven to 170C) and I have found no problems from leaving it a bit longer than most internet suggestions I found.

[DX-SFX]

If the plastic is drooping under it's own weight, that's more than hot enough. If you're not getting the plastic to pull into the detail, you may have to drill tiny evacuation holes to allow the trapped air out. While applying the vacuum, you can also heat local areas with a hot air gun to keep the temperature of the plastic up. The other more likely cause is that your vacuum isn't strong enough or there's an air leak somewhere, both of which are common on home built machines. Vacuum cleaners are nowhere near the same as a proper high vacuum pump.

[tonyG2]

I haven't "graduated" to vac forming just yet but do do a fair bit of plunge molding to make canopies and basic shapes.

Thats kinda of the first step in vac forming.

Anyway, like DX-SFX says, if its drooping then you are ready (not often a guy hears that one ).

Beyond that the main problem (other than the vacuum system - no idea there) can be too rapid cooling. What is the air temp in the room for example.

When I'm doing some plunge molding, I whack the central heating to max and put the fire on full and let the room get REALLY hot before I start.

Also, what thickness of sheet styrene are you using? THat can affect results considerably.

Nice tip about the hot air gun. Hadn't thought of that.

[davidlgreen]

http://i238.photobucket.com/albums/ff42 ... CT0786.jpg

what can i do to improve this? thanks for a taking a look any and all ireverant posts apprieciated

[DX-SFX]

Not sure if this applies to the unit pictured but on a conventional former, if the plastic sheet leaks air around the edges because the sealing strip is failing, you can put sticky tape around the edge of the sheet to make an air tight seal before putting the clamp in place.