Annealing extruded acrylic

[Mick BaileyParticipant @mickbailey28509]

As a side project I’ve machined up some guitar pickup mounting rings in 4mm extruded acrylic sheet (PMM). Size is 4″ x 2 1/8″ and with the cutout there’s about 3/8″ border. Drilled and countersunk on the corners.

Is there any mechanical advantage in annealing them? Cast rather than extruded would have been a better choice, but I’ve used what’s to hand.

If annealing is necessary I’ll use my toaster oven with a Variac and give them a few hours at 85 degrees C.

[Mick BaileyParticipant @mickbailey28509]

Annealing in this particular instance wasn’t any benefit as far as I can see. There’s some unwanted shrinkage and no discernable change in strength.

I think the main advantage is reducing stress cracking with exposure to some hydrocarbon fluids, not relevant with these parts. I have experienced this with using solvent degreaser on an acrylic mororcycle tail light lens years ago – the plastic crazed instantly throughout its thickness and showed all the stress lines quite clearly.

[bernard towersParticipant @bernardtowers37738]

I have annealed some ext/cast acrylic with mixed results. items with quite a bit of machining on them(sharp corners/holes/threads etc) seem to benefit more by releasing the stresses built up by machining. I do mine in the oven at about 80 degs

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