RE: [atm_free] Re: perforating primary
Thank you very much for the detailed information and advice. I did read some books and web sources, but it’s good to get the opinion of someone who has recently built similar scopes.
I guess that my best option is to core from the back to within a few mm and finish drilling from the front after figuring. I know that I’m going to stress a bit while drilling that last bit, but it has to be done. Hopefully the surface won’t scratch (much) around the perimeter of the hole due to me using a diamond hole saw.
- Guy I recently had occasion to have a disk trepanned from a larger
The mirror was parabolized and coated. Since the intention is to
refigure the mirror from F-8 to F-15, I had no concerns for the surface
or the coating.
I watched as the machinist zeroed the disk on the platten in the water
and then stood there in awe as the water jet scribed a precise cut, all
in about 2.5 minutes!
On close inspection with a 60x scope, the surface was flawless! The
geometry was also perfect.
When I consider the time spent making large custom diameter hole saws;
the time spent setting up a vertical mill; the time spent cutting the
disk, the time spent cleaning the mill of abrasives, I've pretty much
concluded that I'll not likely ever use a hole saw to treppan again!
--- In firstname.lastname@example.org, "Mark Christensen" <mjcw500@...> wrote:
> Diamond corer or not the idea of coring glass (to use the
> A.S. term), which itself produces abrasive particles -
> the glass, on an expensive piece of gear would scare
> the Willies out of me as well.
> Sounds like a job for a cheapie (but not too cheap - you
> don't want a lot of wobble) drill press. I regularly abuse my
> oldie from Harbor Freight (1980s vintage), even using it
> as a (manual) polishing and figuring station for 10 inch
> and smaller mirrors since it has a rotary base and
> adjustable height.
> I'd like to add my thanks for the link to the Hong Kong
> coring tool company as well: I needed to get several of
> these and was on the verge of spending $50+ apiece for
> them from other sources.
> Mark Christensen