How to avoid ceramic platen cracking?

L

Leon Husock

Joined
Jul 17, 2019
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320
On two different occasions I've gotten ceramic platen plates (the kind that look like glass) and mounted them to the platen for my Grizzly with JB weld epoxy. Unfortunately, the Grizzly platen isn't perfectly flat, and curves very slightly convex at either end; while I've filled in the gap between the platen and the ceramic plate with extra epoxy, inevitably I get a little crack along the width of the ceramic right where the curve starts. The epoxy has always held with no problem, but sometimes the little crack can cause irregularities in the grind, and it's just less than ideal in general. Is there any way to avoid this? I don't currently have access to any means of flattening the Grizzly platen such as a milling machine or disc grinder.
 
You have to have the metal platen flat.

You may have to fabricate a flat platen for your machine and then adhere the glass.
 
AVigil said:
You have to have the metal platen flat.

You may have to fabricate a flat platen for your machine and then adhere the glass.
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I was hoping there might be another option. Maybe I can weld a flat piece of steel to the existing platen (easier for me than than fabricating a whole new platen since I only have a 110v welder).
 
Flattening by hand is easy, if boring and tedious and labor intensive.

Get something flat, like a piece of granite countertop or a thick piece of glass. Tape or glue some sand paper to it.

Put whatever you want to make flat on it and move it in figure eight patterns. After a few figure eights turn it 90 degrees, then do it again.
Continue doing this, checking the underside scratch pattern until you have an even scratch pattern across the whole thing.

That's all there is to it. Simple. Boring.
 
A.McPherson said:
Flattening by hand is easy, if boring and tedious and labor intensive.

Get something flat, like a piece of granite countertop or a thick piece of glass. Tape or glue some sand paper to it.

Put whatever you want to make flat on it and move it in figure eight patterns. After a few figure eights turn it 90 degrees, then do it again.
Continue doing this, checking the underside scratch pattern until you have an even scratch pattern across the whole thing.

That's all there is to it. Simple. Boring.
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Unfortunately I think the grizzly platens need enough material removed that it would take me a very long time to do. But it's certainly a possibility.
 
Use an angle grinder or something first, or a file. Then start with 80 grit paper...
 
Whether you get your platen flat or not, make sure you're not clamping the glass too hard while the JB Weld cures. In fact, don't clamp it at all if you can help it. If the glass is under any kind of tension while the epoxy cures, it's likely going to crack, sooner or later.
 
Drew Riley said:
Whether you get your platen flat or not, make sure you're not clamping the glass too hard while the JB Weld cures. In fact, don't clamp it at all if you can help it. If the glass is under any kind of tension while the epoxy cures, it's likely going to crack, sooner or later.
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Ohhh, that's interesting. Both times I've done it I clamped the crap out of it. I wonder if that was the problem, since in theory if the epoxy is fully cured I feel like it should provide enough support pressure from grinding shouldn't cause the glass to crack.
 
Leon Husock said:
Ohhh, that's interesting. Both times I've done it I clamped the crap out of it. I wonder if that was the problem, since in theory if the epoxy is fully cured I feel like it should provide enough support pressure from grinding shouldn't cause the glass to crack.
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That's likely the reason it cracked then.
Another thing: Make sure you're putting a ledge on the bottom of your platen for the glass to sit on, so that if the epoxy were to fail, the glass won't fall down into your wheel and become a frag grenade. Here's a pretty good vid on how to do one:
If you don't have a welder, you can just drill and tap the bottom of the platen and put a couple of machine screws through it.

Instead of clamps, I'd probably just lightly wrap some masking tape around the glass and platen to keep it from shifting, and let it cure.
 
I have the grizzly and I used the contact wheel to get the platen flat and glued the pyro-ceramic with jb. I have been doing heavy grinding on it for 5 years without a problem
 
If the steel platen bends away from the glass at the ends (convex), and you then clamp the glass and steel together while bonding with JB Weld, you will be putting the grinding face of the glass in tension. Either bending the steel towards the glass, or bending the glass towards the steel. You only get "filling" of that gap with epoxy if you didn't clamp the ends together at all, just left it free to self level. Grinding causes heat, heat causes expansion, all of which is going to put the grinding face of the glass under more tension...*crack*.
 
Something to add, I didn't clamp anything. I put a generous amount of JB on the platen, laid the glass down, moved the glass back and forth to get any bubbles out and gently pushed down with a flat piece of wood. I used the wood to keep the pressure even to avoid cracking it.
 
Ian Fifelski said:
Something to add, I didn't clamp anything. I put a generous amount of JB on the platen, laid the glass down, moved the glass back and forth to get any bubbles out and gently pushed down with a flat piece of wood. I used the wood to keep the pressure even to avoid cracking it.
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Well I didn't think to move it back and forth to get rid of any bubbles so I do have one little air pocket all the way at one end, but not clamping worked perfectly! I ground on it all day and no cracks. Thanks for all the advice, guys!
 
I’ve heard people using double sided carpet tape, I never have thou‍♂️ I always use JB Weld, a crap load, get the glass where you want it and tape it with blue painters tape. Set overnight and ur good to go! YMMV!
 
NickBoyle said:
I’ve heard people using double sided carpet tape, I never have thou‍♂️ I always use JB Weld, a crap load, get the glass where you want it and tape it with blue painters tape. Set overnight and ur good to go! YMMV!
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This is faster...............
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