HELP! Urgent advice needed re bending clear styrene!

Weaver · March 16, 2011, 11:35:19 AM

I'm trying to make an aftermarket windscreen for a model motorbike. The real thing is a curved sheet of thick plastic, so I thought I'd use hot water to bend a smaller one from clear stylene:

Attempt 1: screen taped to a former to give it a "forced" curve, dropped in boiling water for a few minutes, then plunged into cold water. Result had "set" fingerprints and tape marks that wouldn't polish out at any price.

Attempt 2: screen polished, then covered with masking film on both sides. Taped to former with waterproof tape, dropped into boiling water and left in to cool naturally. Result: screen has correct curve and no fingerprints, but is misted by what I suspect are micro-cracks inside it's structure, which no amount of polishing will remove.

So, how do I put a permanent bend in a piece of clear styrene without either spoiling it's surface or misting it internally?

This model MUST be ready by Saturday at the latest (completely non-negotiable), so I need to know ASAP whether or not to persevere or give up.

Any and all advice gratefully received.

jcf · March 16, 2011, 12:21:04 PM

Hi Harold,

previously formed clear styrene is notoriously a bugger to work with as it is basically 'pure' styrene with little or none
of the plasticizing compounds that make the coloured versions relatively easy to work, as a result it is brittle and easily
cracks.

Clear acetate, or PETE would be a more workable choice. Do you have any leftover clamshell packaging around the
house? This is generally PETE (recycle number 1) and it can be hot-formed and cut with scissors, the edges will take
gentle sanding/polishing. Use CA to attach it to the fairing.

HTH

Weaver · March 16, 2011, 12:26:05 PM

Cheers Jon.

I'm looking at other plastics at the moment.

The bike doesn't have a fairing: it's an aftermarket screen attached to the handlebars by two long, thin brackets which are incredibly fragile in 1/12th scale. This is why the curve has to be pre-formed: if I used the brackets to hold it in a curve then it's "spring effect" would just break them, because they're glued onto plastic, not clamped onto steel.

deathjester · March 16, 2011, 12:40:08 PM

Do you have any soft drinks bottles at home? Cut a 6''x6'' square, mount your former on a pole in a clamp/vice. Using a candle, soften the middle of the plastic by holding 4'' - 6'' above the top of the flame, then quickly pull it down over the former. Hold for about 3 secs.

frank2056 · March 16, 2011, 01:17:41 PM

Quote from: deathjester on March 16, 2011, 12:40:08 PM
Do you have any soft drinks bottles at home? Cut a 6''x6'' square, mount your former on a pole in a clamp/vice. Using a candle, soften the middle of the plastic by holding 4'' - 6'' above the top of the flame, then quickly pull it down over the former. Hold for about 3 secs.

Without a doubt, do ^^^this^^^. It's a lot easier and quicker than you'd think, and if you start with a soft drink bottle, it'll be "precurved". Just pick one big enough to have a curvature similar to the windscreen. If you screw up on the first (or forth) try, try again.

Weaver · March 16, 2011, 06:45:26 PM

Solved it!

I found some of those plastic stiffeners that come in the collar of new shirts: same thickness as the styrene but softer, and it took the hot water forming without a mark.

Thanks guys - much appreciate all the help.

rickshaw · March 16, 2011, 10:19:58 PM

Thats good. I'd have warned against using a candle 'cause it would more than likely leave smoke/soot on the plastic, embedding it in the softened plastic. I've seen a small burner made from a jar, filled with cotton wool and part filled with Methylated Spirits and a wick made from cotton string soaking in it, poked through a hole in the jar lid, used for heating plastic. It burns with a relatively low temperature, clean flame without smoke or soot.

deathjester · March 17, 2011, 03:24:13 AM

That's why you hold the plastic clear of the flame - then it doesn't get burnt or smoky. I do like the idea of that sootless burner though!

dragon · March 17, 2011, 10:36:12 AM

Hopefully you did dip those "failed" attempts in FUTURE (or local equivalent) prior to discarding them, right?

Weaver · March 17, 2011, 11:21:56 AM

Quote from: dragon on March 17, 2011, 10:36:12 AM
Hopefully you did dip those "failed" attempts in FUTURE (or local equivalent) prior to discarding them, right?

Yep - thought the micro cracks might be on the surface in which case Future would help. They wern't and it didn't....

I tried bending a piece of the styrene with the help of a hairdryer, but it tended to set so fast when the heat was off it that it ended up wavy. Didn't help that my ideal-shape former was a plastic (polyethylene? Thick, greasy stuff...) paint brush holder, so I didn't want to heat the styrene on there in case it distorted as well.

Currently trying to make a 1/12th scale fake carbon fibre tank protector look right.....