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Anybody cnc mill glass before?

Going to take a class on telescope lens grinding, so Iv'e been reading up how...to get a head start. Relatively simple lapping process by hand. By lapping two mirrors together they naturally create an arc. When your done, you parabilize the lenz. So I was thinking, screw that, the glass blanks are halfass ground flat on the back. Say a 10 inch dia blank. So you use a vaccum chuck to hold it down, and cnc mill using whatever grinds the best the exact parabolic curve you want. Then, diamond polish it when done. machine it real fine using a spiral cut, making a few tenths stepover. Let it run for a few hours. Then some diamond polish. As opposed to 8 hours of hand roughing, followed by 3 hours of polishing just to get an inaccurate form.

So I'm trying to figure out what to cut it with. it polishes with aluminum oxide lapping dust so I know a regular grinding wheel will cut it, then there's borazon and diamond?

And why are people hand lapping them to shape, why isn't cnc being utilized?

Reply to
vinny
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Hi Vinny, Yes, you can rough a blank in a CNC with some sort of abrasive wheel, however, you are always going to cause some sub-surface damage which must be removed. Many TMs are starting with pre-generated blanks these days and start lapping with 220 silicon carbide free abrasive. As to why glass: Stability. remember you are going for an Angstrom class surface finish and a small handful of nanometers in form. Vacuum chucking it to a machine is a sure way of generating a potato chip form. The best advice I can give is to go to the class and listen to what they have to say.

Reply to
jeff

Great advice. Funny, before I posted to this group I figured I could do it no problem. But after a few things from man without a country..I mean man without foreskin, lol, I researched some more. There's more to this than It seems. The surface integrity seems to be the key, way more important than the shape of the form. And I can see the mill putting a vibration into the glass. I am going to the workshop, and I'm not even going to mention I'm a toolmaker. I will be a piece of clay.

Thanks for the advice.

Reply to
vinny

Grind with diamond, and keep the area WET. You have to carry off the heat from the grinding or the local concentration of heat will crack the glass. I'm CNC machined glass, but it was thin strips of glass, like .031" thick, and I was putting rows of V grooves in it.

Jon

Reply to
Jon Elson

You still need to lap but fastest I've seen for hogging on a vmc is to use a horizontal rotary to spin the blank and cut using a fairly large dia diamond wheel in the spindle.

Reply to
Jeffrey Lebowski

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