Machining Coated Optics?

[Fasttrack]

I was recently asked if I could put a hole through a parabolic mirror. In principle, it is very simple. However, I am concerned about getting through the reflective surface without any damage... the mirror body is aluminum and the reflective surface is gold with a Al(MgF2) coating a few microns thick. I told them I would get back to them later after I had a chance to scratch my head. Any thoughts on the feasibility? What would happen if I eased through the surface from the back?

Here is a similar product:

http://search.newport.com/?x2=sku&q2=50338AU

[jlevie]

I'd coat the reflective surface with two or three sprayed on coats of shellac or lacquer to protect it. Then drill undersized from the back and finish the hole with a boring bar, taking a thou or so per pass. Remove the coating by soaking in solvent.

[RichR]

That's basically what I was thinking except maybe drill most of the way oversized so you only need to bore the last 1/4" or so.

[jlevie]

That would work fine. The point of boring to final size is to wind up with a clean exit hole.