I want to make a curved screen out of polycarbonate. a 1.5m single radius across a 0.5m width sheet, which will be 0.9m long. For those who find it hard to visualise, a 20mm rise in the centre of a 500mm wide sheet.

How do I do this and get a nice even radius across the whole sheet.

maybe drape moulding (if thats what its called)

Make a former out of wood to the required curve. Clamp the sheet to it then heat it carefully with a heat gun.
Should the drape over the former and set to the shape.

Yes drape forming or moulding is about the only way to do this. The major issue will be heating the piece uniformly to temperature. You could attempt to make you own oven using something like A/C ducting and a heat gun. The former could be something like aluminium or steel sheet that has been passed through a set of rollers to get the curvature. Or a laminated block of MDF.

JC

if you can borrow one of the mobile heaters of a paint shop, you could use that to heat the sheet. Otherwise find a big oven, main difficulty is to heat it as a whole as heat guns tend to give uneven spots and don't look nice

I would try making a wooden frame to hold the sheet in the correct curve, its natural springineess will dohat, then find a way of warming it til it relaxes into its new shape.

I presume that it isnt going into a frame when in use?

John

Same technique they use for forming glass. only obvously not nearly as hot, and for glass you have to use ceramic formers.

As mentioned, the hard part is heating it evenly, and the right amount, and slowly enough.

Only other way is a bloddy big vac former. But again you need the equipment.


Daniel

Has anybody successfully made a bonnet out of the stuff, and heated to shape with a gun?? I can gets lots of the plastic...

as above tricky to heat uniformly and as soon as it is just a couple of degrees too hot you get bubbles which spoil it completely.
Takes loads of heat to get to shape as well

Depending on what thickness material you're using, you might even be able to cold form it. 3mm polycarb should be easy enough to form to a windscreen shape without heating.

If you need to thermoform the sheet, here are some tips that I picked up from the plastics game when I was in it:
- Polycarb is hydroscopic so get the newest sheet you can and make sure it's got the protective film to protect it
- Since it's hydroscopic, heating it quickly will cause the water to evaporate causing the bubbles. Apparently heating up the sheet slowly helps to counter this.

You might even want to look at alternatives such as Vivak. I can't remember what the chemical composition is, but it's somewhere between polycarb and acrylic (perspex) and should be easier to heatform.

WRT to the polycarb bonnet - I wouldn't.... I briefly considered this or polypropylene for my bonnet but neither has brilliant heat resistance and both will expand a lot and/or warp when it warms up.

HTH,

Tim