Can I vacuum form from a plastic master w/o melting the master?

[Len Woodruff]

I tried this with a clear windshield and it melted some. This would be the normal white plastic that has been modified.

[OldNYJim]

Having some professional experience of vacuum forming, I would say no.  If the heat is high enough to soften the plastic sheet that you're using to form, I would be surprised if it didn't damage whatever the master is too.

 

[Ace-Garageguy]

5 minutes ago, CabDriver said:

Having some professional experience of vacuum forming, I would say no.  If the heat is high enough to soften the plastic sheet that you're using to form, I would be surprised if it didn't damage whatever the master is too.

 

Exactly.

However...if the master is cool, and the clear plastic is heated to its "glass transition temperature", about 100C or 212F for styrene (lower temps probably work fine for vacuum molding, but I have no detailed records to quote at this time), the clear sheet can be "sucked" over the master with no ill effects if you work fast.

Vastly preferable is making a master that's temperature-stable well above the temp where styrene or PET is fully workable.

My go-to for molding plugs from existing styrene parts is MGS 285 epoxy, which is stable to at least 250F if post-cured properly...but at $400/gallon (including hardener), it's not everyone's easy solution.

[OldNYJim]

Of course, that post of mine wasn't very helpful because it didn't tell you what you COULD do.  If you had a bunch of time and effort sunk into a project and didn't want to make a brand new master (but still wanted to vac form copies), I would resin cast it, with some extra material underneath to make a 'block' that you can pull from - regular resin, if cast thick enough, is generally plenty sturdy enough to at least a FEW pulls on a vacuum former.

Alternatively, a fine grain hard wood (not balsa) can be used successfully as a material for a master. 

A kind of 'poor man's' vacuum forming I've seen done before is using a hobby heat gun and a clear coke bottle to 'shrinkwrap' a part...I never did it myself, but I've seen people use a similar trick to make a down and dirty copy of something in clear plastic without the trouble of making a 'real' master

[OldNYJim]

Oh, nevermind, Bill covered (much better) the same stuff I said in my followup anyway

[Len Woodruff]

Thanks so much everyone for your feedback.

I am glad I didn't try it before I asked. 

I think the choice would be to make a resin master. Then I can either make more of those or do the vacuum form using the resin piece.

 

 

[stitchdup]

If your not going to be using it in vac former too often you could use cheap car body filler and use it to make a buck for forming from. if you cover the back side of your master with cling film (i think you guys call it saran wrap) you can build a small box around your master then pack the box with filler for a buck to form from. It should work for a few tries, possibly more tries if you made it bigger so you can trim back  the window and being made from body filler you can remedy any flaws easily. Even the glassfibre filler would work but its more likelly to have bubbles

[oldcarfan]

As a general rule, I'd say no you can't. But I've made copies of windshields, hoods, fender flares and fairly flat stuff by filling the backside of the part with plaster of paris to give the part some support.

[Gramps46]

In olden times I would carve wooden forms or make them from Bondo for windshields or tops.  Of course that doesn't solve the replication of existing parts.  It's past my knap time.

[Len Woodruff]

Thanks Guys. I was able to make a resin copy. I can use that to vacuum form.

What thickness of white plastic do you use? I use thee .020 Pet-G for the windshields.