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Ceramic radius platen? Any new info?

Ah, no. Not yet! I went as far as buying some borosilicate glass and cutting it to size (I have enough to attempt the slumping a few times). I really need to get around to doing it...

It's the annealing of the glass that gives me pause. The softening temperature of my glass is given as 820 C, and the "working" temperature is given as 1270 C, so presumably the slumping temperature is somewhere in there. However, the annealing temperature starts at 560 C, and needs a slow cooling from there. The problem is that nasty things happen to the glass the longer it stays in the working range. So you need to basically heat it up fast (or preheat slowly and evenly to around 540 C and then crank it) , get it slumped, then cool the kiln quickly to 560 C before you start annealing.
 
Wonder if you could just cut the radius with a wire edm?
 
I was looking into getting a custom 400-600 grit diamond wheel made that had something like an 1/8" and/or 3/16" cove, but I seem to have misplaced the name of the company that I was going to get a quote from, and haven't been able to find it since. I tried rounding over some class with a 1/4" cove bit in my milling machine, which did work "OK", but the finish was too rough for my liking. IIRC it was about a 120 grit diamond cove bit.

EDIT: I just realized you're probably talking about a large radius platen. I was thinking about a flat platen with rounded corners on the long sides for plunges and such.
 
I'm not sure if borosilicate glass is electrically conductive, but I chose that material instead of ceramic glass because boro can be slumped (pyro ceram can't, apparently). I've been concerned about devitrification on the platen's surface due to prolonged exposure to high heat (kind of like the decarb of the glass making world), but maybe it's not such a big deal. I don't know whether it's just a cosmetic flaw, or if it would significantly weaken the platen. For what it's worth, my small amount of research suggests that I should slump the glass over a radiused piece of steel instead of slumping it into a depression. I have a steel radius platen already, so I may just use it to form the glass, but it will ruin the heat treatment. That said, it's 5160, so shouldnt be hard to harden again if I want to...
 
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