Hi, what clear plastics can you vaccuum form (with heat to soften) Thinking of something suitable for light covers so not too brittle. Not sure if acrylic would be suitable maybe?
And also can you do vaccuum forming in a bag like you do with glass/carbon fibre? Ive only ever seen it done in a big box with really thin plastic. Any other suggestions welcome? Thanks

I have formed some clear plastic that I bought from HomeBase by putting it in the Oven on a low heat and then pulling it quickly over a wood former. The plastic goes a bit like rubber so some double curvature is possible. I think that the plastic was acrylic but was a little brittle.
Some trial and error was required both for the former and the temperature to make suitable end tanks for a home made solar hot water panel.
The program 'Hitler's Stealth Fighter' a couple of weeks ago showed the process with trial and error making a replica cockpit canopy.

Brian Thompson used 2 mm polycarbonate and vacuum forming for his headlight fairings according to the pictures in his book 'How to build your own Supercar' but the moulds do get rather complicated.

you can vac form acryllic. You can also use petg but that is not uv resistant, unless its coated, still wont last as long as acryllic though.
i have a fairly large vac former so if you wanted something made over a form of yours give me a shout.

Thats good of you to offer thanks.Would 2mm be about right then? I was thinking thicker, but only guessing. What about polycarbonate? Just been watching vids on youtube and it doesnt look that difficult to make a box one either so might give that a try too if i go for it

[Edited on 3/11/10 by andrew-theasby]

acrylic (perspex is common brand name) is thermo formable, but willcrack or shatter in an impact, a stone thrown up at 2mm would do it imho.
Clear polystyrene is a tad more flexible and more likley to survive but probably less scratch resistancebut cheap as chips so you could make a few very cheaply. Often tell polstyrene as it gets white stress marks if creased or impacted.
Polycarbonate is by far the best material, great impact resistance (they make bulet proof windows and riot shields from it!), common trade names Lexan and Macralon. It vac and thermo forms well but not easy to do effectively DIY. Its got a really narrow temp window, too cold and even Monica Lewinski couldnt suck it into place, and a gnats too hot and it blisters the surface badly.

for either non vac thermo forming info (ABS, polsytyrene, acrylic) search for articles on R/C model aircraft canopy How To's, loads of info to read up on.

CNH

As above , we have a smallish machine and temp for clear stuff is critical as if too hot it goes milky.

For DIY projects like your lamp covers, plug and yoke forming can give good results so long as you have an oven big enough for the sheet you start with and some decent ply wood drill and a jig saw.
hth
Mike

quote:

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Originally posted by CNHSS1
too cold and even Monica Lewinski couldnt suck it into place
CNH

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You make a solid former to stretch the hot plastic over but to make it more effective there is a close fitting surrounding frame with a gap the thicjknes sof the material used, which ensures repeatability. Basically you drape the plastic over the former then put the frame on and press it which stretches material into the desired shape and hold it until plastic is cool when the excess material can be trimmed off.
Effectively the frame and press replaces the vacuum.
hth
Mike

Sure does thanks, ill let you all know how i get on, but it may be some time!!

if you want to be a really clever type, you make the formers with an inch thick skim of liquid metal (usually ally powder impregnated resin) and heat the formers.
This stops the first bit of the plastic that touches the former cooling, and giving you a moulding with a thicker centre and progressivley thinner section towards the edges.
with a bit of practice, you can sort of compensate with just wooden formers, buy heating the centre of the plastic more than the edges and sort of radiate out the heat from the centre getting less towards the egdes.