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Old 05-24-2018, 02:29 PM
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Pete VanderLaan Pete VanderLaan is offline
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Join Date: Apr 2002
Location: Chocorua New Hampshire
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If a piece can't survive sitting by itself after being out of the lehr for two hours, it really is not close to being compatible unless you're talking some massively thick thing. A regular glass, in the shape of a cylinder, about 1/4-1/3 inch thick, about three inches in diameter will do admirably. Do make sure your saw has adequate coolant and the blade has diamonds on it.
If the piece cracks, almost with a shudder, the moment the blade touches it and breaks the surface tension, you were way far off. You really should be able to saw the ring ( about an inch inch wide). My experience tells me if the ring survives that, it's compatible. I've seen some exceptions marrying lead to soda lime where it can take an hour or so to crack after that but in general, similar glasses are good matches at that point within the constraints of 1.5 ten thousandths. The vertical score that you tap clean is going to tell you how to fine tune the glasses and we outlined that as a graphic in glass notes, so look at the graphic.

John prefers the Hagy seal and I get that. It's worth noting that if the Hagy seal is more than about 2.0 off, it breaks before you can ever test it. The ring doesn't have quite the same issues. If the glasses are similar, you can do a simple pull test with canes and they will tell you a lot as well. They're in the lassnotes IV as well. If you don't own the book, you really need to get it. Henry put together a great compendium.

At any rate, you don't need to cool it that long. I just put mine under cold water before sawing if I think it's a bit warm. If that breaks it you need to change your glass.

Do keep in mind what annealing is doing and the range in which it happens. From deformation point down to Strain point, you can relax the inherent tension in your glass. Soaking the piece is the most critical aspect of the process. Putting it away hot enough to not need to overcompensate is important as Frank Wooley noted long ago. The thickness and the rate of reduction of temperature are indeed important down to Strain Point but remember that once you pass Strain Point, no further annealing can occur. At that point you're just trying to prevent thermal shock.
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