In the process of designing a hardtop and wonder if its possible to bend clear perspex to follow the small radius of the rear tub keeping it clear.

Is it simply a process of gentle heating and bending round a tube of the same rad??

Steve

Yes, it's perfectly possible and surprisingly easy. I've done it by simply playing a blowtorch over the perspex as you bend it round a suitable former.

The main trick is to give it enough heat to make it pliable, without letting it get too hot, otherwise it blisters or goes cloudy.

You want polycarbonate (Lexan) rather than perspex, though.

A hot air gun will work fine. The secret is to keep it moving and you really need to heat from both sides since the plastic is a very poor conductor. There is quite a fine line between 'nicely flexible' and 'very floppy' and you almost certainly don't want to reach the latter stage if you are trying to form a simple curve!

Make sure the plastic and the former are both perfectly clean, or you will embed grit/dirt into the hot plastic and it will be almost impossible to remove.

Ideally make a proper jig where you can clamp the sheet down as it cools - it's difficult to hold a steady angle by hand for the length of time needed to fully cool the plastic.

I tried and failed, although it may have been down to the propane torch I used to warm it up!

As said a very fine line between stiff and unflexible and very flexible and bubbles, as as said lexan is the gear you need as perspex shatters, you can bend lexan without heat quite alot so thats maybe an option if it can be bent into a jig and the warmed up it situ to "fix" it is place??

Cheers

R

The thinner the material the easier it is to get a bend on it.

Regarding Lexan, the reason it goes cloudy is because as time goes on it adsorbs water, so when you heat it you get tiny steam pockets that give that cloudy look.

The datasheet says to dry it out over a period of time (special oven) and then it bends without clouding.

http://www.theplasticshop.co.uk/plastic_technical_data_sheets/lexan_polycarbonate_9030_technical_properties_data_sheet.pdf

There is a fomula for bending polycarbonate which I think is 50:1 meaning you can bend a 6mm sheet round a 300mm radius without stress whitening or deformation.

I wouldn't use polycarbonate tho'. It is many times the cost of acrylic and very vulnerable to scratching and abrasion. You could buy Marguard or similar which is an acrylic capped polycarbonate but that is another factor of cost again.

Heat forming acrylic is really easy with a heat gun. Never use a propane or butane torch, the heat is too localised and will blister the surface. Follow all the advice already given, but also remove the protective film first. It will burn off before the sheet bends and mark the surface. I tend to 'freehand' bend without a former as you avoid marking the surface. Let gravity do the work.

The lower cost of acrylic allows you to do lots of practice bends.

quote:

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Originally posted by plentywahalla
Never use a propane or butane torch, the heat is too localised and will blister the surface.

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its all in the wrist, i dry my trousers with a blow torch, whilst wearing them! And no, not when i wee myself, i mean when i get wet knees at work!

The commment regarding polycarbonate versus acrylic is in relation to where you are using it. Far better to use polycarbonate if it is in line with you in a vehicle as if it is hit it doesnt shatter and cut you to pieces as acrylic will!!!! Another way to heat acrylic is by using an electric element fire (if they are still around) If you want a narrow strip bent, place steel sheets with a gap in them over the element then heat it turning regularly. If you under heat acrlic and try to bend it, the ends of the bend can split and the face of the bend wrinkle up.

We have used all of methods described so far - main thing is not to get any blisters, we also have an oven which is pretty good and a heat pres as used for T shirt making etc and that is really good as the temp is controlled- kids can do plug and yoke moulding which they find impressive.

How big are you planning Steve- is it for a Nissan Cube style rear window or similar?
atb
Mike