Windscreen shaping

[ryanmech]

Can anyone supply info on shaping a windsceen out of perspex sheet? or direct me in the correct path....

I have the original broken and glued together screen, which i intend on using to mold the new one against.

What i don't know is if i can just simply heat the sheet up to temp and mold over the original? Also i don't know the temp at which i should be doing this at...

any help much appreciated

Ryan

 

[patprimmer]

For slight curves you can just heat it on one side with a hair dryer.

It will curve away from the heated side.

It will take a bit of practise to get it right.

Big pieces are more difficult than small pieces.

Other option is to heat it in an oven to 160 deg C, at which point it will be in a rubber like state.

You can then drape it over a mould and allow it to fall into place.

Take care not to damage the soft surface.

It is better if you can also heat the mould or cover it with a soft smooth fabric so the surface does not chill before the shape is formed.

Regards
pat

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[ryanmech]

Thanks Pat

That is exactly what i am after. awesome

The windscreen is off a motorbike and the molded acrylic sheet will be about 400x500x3mm. I will follow as you have explained using a oven to get up to temp, then will mold over the original, clad in cloth.

Are there any concerns with doing the above with a very dark shade of black perspex? Do colours have any impact on the properties at molding temps?

Regards
Ryan

 

[patprimmer]

Colours do change the moulding characteristics a bit, but all colours still mould OK by the technique mentioned earlier

Regards
pat

eng-tips, by professional engineers for professional engineers

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[nbucska]

You can use the original -- it would soften and bend, too.
I suggest make a plaster of Paris negative, cover it with
a wet cellophane sheet -- when it dries, it will be smooth
and shiny.

Hair drier may not be hot enogh -- there are similarly built industrial heat guns...


<nbucska@pcperipherals.com>

 

[nbucska]

Sorry -- "you can't ...."

<nbucska@pcperipherals.com>

 

[patprimmer]

For gentle curves on small mouldings, HAIR DRYERS DO WORK. This is not theory, but fact gained from personal, first hand experience.

For the large curves of a motor cycle screen, you will need to heat the sheet in an oven.

If you use a fabric over the original screen, the new screen should be formed before the old screen heats enough to distort. To be safe, use an old blanket as the overlay, or back up the old screen with some fibreglass or with plaster of paris.

Regards
pat

eng-tips, by professional engineers for professional engineers

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[ryanmech]

Yeah
before you fellas have a fist fight i will give it a go and see what happens. I glued my original windscreen all together last night and put struts on the rear of it to hold it in its natural position. So thanks 'Nbucska', but i had already taken bending of the original into account.

The sheet of perspex is only going to cost me NZ$9=US$13.70, so i could have fifteen goes at it and it would still be cheaper than buying a new one, which has most likely been molded off an original.

Okay thanks and thanks

Ryan

 

[ryanmech]

Thanks you fellas

i tried to mold the screen, and was successful to some degree.
Unfortunately i got a hot spot and some of the perspex bubbled up, but i will sort this next time by putting the oven on fan bake. Should have asked my mother about this.

I found that the best way to mold it was to lay the hot sheet onto a bed sheet or similar and then place the mold on top. Then lift the bed sheet by the corners and the perspex automatically takes the shape of the mold.

No problems

Cheers
Ryan