Perspex as dial glass replacement material

[60 oldjohn]

I have a Cossor 464 the original Celuloide cover had shrunk and I made one out of perspex. My mistake was to make it a perfect fit, not tight but "snug" and held in place with Areldite. Ten years on and Hairline cracks are apearing at the corners of the aperture in the Bakerlte. The perspex expands at a different rate to the Bakerlite. I dont use the set so no heat from bulbs, just natural temperature vairiations. I think I should have made it smaller and fixed it with clear Sillicone.
John.