In the production world, blanks are cut, edged, and then coated. Going backwards, ie coated, cut, edging, results in damaged coatings.
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Usually the blanks are cut using a diamond impregnated wet blade (diamond saw or lapidary saw) and then coated.
One of my friends, a PLer, has a wet, diamond bladed, lapidary bandsaw for this, but he sticks to much larger mirrors.
It is cheaper for a laser hobbyist to buy a large mirror and cut it, until you get down to galvo mirror sizes, then its expensive because you break it.
The 5" diamond bladed saws with water cooling start at 2000$ each.. Blades are about 10-30$ each.
If you had a lathe, you can make an arbor and use a lathe to hold the diamond wheel. They spin at just a few rpm to a few tens of rpm and are quite tame for handwork.
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If the glass is annealed the right way, for thin blanks a robotic diamond scribe is used. After the blanks are scribed
they are manually broke along the scribe lines with a very high loss rate.
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One of my college jobs was breaking the machine scribed glass in a LCD display plant, then coating it. Our losses were huge.
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Now for the down side, you have zero control over the annealing state when you buy a stock coated mirror. Sometimes I get stock that is annealed correctly for cutting and dicing. Other times... Well, its shatter city.. Its not something vendors care about, unless your ordering a huge amount of custom mirrors.
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Other lens and mirror blanks are ground to shape prior to cutting, using a silicon carbide or diamond wheel, and in some cases a diamond tipped lathe.
We do some course and fine hand grinding at work using special belt sander belts made for glasswork.
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Generally cutting after coating leaves a very messed up optical edge. Often the coating will flake, depending on its adherence. Mil Spec coatings are tested for this, civilian dielectrics are not...
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I used to cut my own pre-coated stock for G120 mirrors, which while thin, (0.7 mm) are much larger and easier to handle then modern mirrors. My loss rate was high. That glass vendor is out of business, too. I used a diamond tipped scribe and a ruler, plus glycerin to fill the scratch and aid in breaking. Breaking must be done right after scribing, or the cut starts to "heal" and will not break as clean. In other words, break within a minute of scribing, don't let it set for hours.
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Good Luck,
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Steve
Last edited by mixedgas; 08-17-2016 at 11:57.
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