A parallel plate of optical glass was drilled while monitoring the surface deformations and the transmission quality. Strains along the drilled channel surface were found to give rise to elastic displacements in a radial direction. These strains could be relieved without refiguring the plate.
J. M. Forsyth,
"Letters to the Editor Volume Effects in Drilling of Finished Optical Plates," Optical Engineering 11(4), 114113 (1 October 1972). https://doi.org/10.1117/12.7975910