So you bought this triangular piece of CerVit for $6.00 at a swap meet, and you want to make it into a round telescope mirror. Or you heard that cutting facets in your glass tool cuts grinding time in half (it does), and you’re wondering how to do it. The answer is, sawing!
Twyman, in his 1955 edition of Optical Glassworking (compiled for those actually engaged in making optical work), states that there are three methods for sawing glass. The first uses a diamond charged cut off wheel. (They’re about $60.00 each from Universal, when they’re available.)
The second uses a carborundum cutting disk. He says that it is important that the grit and bond be suitable, and I can testify to the truth of that statement. I used a cut off wheel in a die grinder to groove a 10” tool, and could have gotten the same results if I had tried to groove it with a hammer.
The third method is to charge a hacksaw blade with a mud made from carborundum and water, and to stroke away. He states, “Regarding the respective merits of the three methods, it can be said that the hacksaw method, although slow, is for this reason fairly safe in unskilled hands.”
That’s the one I use.