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Munchma_Koochey t1_izy5qbg wrote

These are all wrong. The purpose of the water is to keep the bit and glass from heating up. When you heat glass locally, its expands and causes tension across the cooler areas. This tension causes it to crack. Drills/saw blades are generally diamond. You're not going to lubricate diamond. Its all about keep all the glass the same temperature.

I was a glassblower for years. I've sawn/cut/drilled many a glass.

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patniemeyer t1_izy6dir wrote

Interesting. I did not realize that the coefficient of friction for diamond is actually lower than oil. That's wild.

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Hanginon t1_izzw8ro wrote

This is absolutely the reason, thermal shock happens when glass is heated and expands unevenly and can be prevented with a flow of coolant across the area and the tool generating the heat.

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Scratch1111 t1_izydax6 wrote

Yes. Heat diffusion and dispersion. I cut holes in glass all the time and we only need to spray water on it to cool it somewhat.

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