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hello everyone im a newbie on this forum (literally my first post) i found you on google!

i have a 3mm-4mm thick sheet of PMMA and i am planning on making some custom light lenses for my car. i want to make a mold of the outer of the original lenses from fiberglass (fastglas or similar) i then want to soften the PMMA enough so that it will fill the mold. there will be some quite acute corners to fill but i want to stay away from using a core mold if at all possible which is why i only want to soften it and not heat it to liquid state.

my only way of heating the size of sheet required is my oven (fan assisted) and i understand that i will have to heat it up gently as not to make it fracture or bubble due to suface heating etc etc.

is there anything else i should be aware of with PMMA?
am i going about this in the right way?
if so what temperatures should i be aiming for to get the desired results?

any help appreciated, thanks in advance

Rich

Hi Rich,

What you propose to do is not such a good idea without the correct equipment.

The perspex workshop manual has some good information.

Heating PMMA in a standard oven is not a good idea as the fumes given off are dangerous and it could also set on fire.

I doubt if you can turn PMMA back to a liquid state by heating it, if you heat it too much it will end up as a blob of molten acrylic.

right ok i do have access to a couple of heat guns and a "2 bar" fire (one of those halogen type) at work would that be anymore suitable?

im only trying to heat a 12inch by 8inch section of sheet so if i could suspend the fire close enough over it would that be adequate.
would i be better of making a core mould with fiberglass and draping the sheet over it rather than trying to fill an external mould?

That would be better than the oven idea.

I have not done any mould forming and so you might need some of the cloth that is mentioned in the workshop manual.

What colour is the lens material?

its a tinted grey transparent material used for external sunvisors on trucks