Pyrex glass instead of tempered?

B

Brett Bennett

Joined
Dec 14, 1999
Messages
672
I am having difficulty finding tempered glass locally for my platen (2X9 1/4 in). They will not temper that small a piece. I bought a piece of Pyrex (according to the shop it has similar properties except it breaks easier than tempered). Before I attach it somewhat permanently, I wanted to throw it out there for comments.

Thanks
 
glass? i don't mean any disrespect but i've never heard of that before, don't you think it would break?
 
Perhaps I was misunderstood. I want use the glass on the face of the platen to reduce friction. I have read other posts in this forum on the topic but all talked about using tempered glass.
 
I would expect Pyrex to be a tough as tempered glass, but if it breaks it won't crumble into small safe pieces. Tempered glass is what they use in car side windows and sliding glass doors. Its most dramatic feature is that if you stick it with an ice pick it crumbles into little cubes. Tempered lenses in eye glasses are probably done differently.

Pyrex is what they used to make the 200 inch diameter mirror for the Palomar telescope. It is definitely up a notch from regular glass. The trouble with glass is that if you scratch it deeply you seriously compromise its strength.
 
I have heard of the glass thing but never tried it.
The platen on my grinder is made of a piece of 1/8" X 2 1/2" O1, fully hardened. It's attached to a piece of angle iron with two 1/4-20 flat head screws. I have tapered the tangs of MANY knives on it and it's still in good shape! If it ever does wear, I can take it off and surface grind it flat again.
Neil

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Kaos,

Of course I didn’t know this was your post, your profile leaves a little to be desired. What is it? “Just because I’m paranoid doesn’t meant their not out to me.” Anyway, I like Dr. Lathe’s idea, glass coming unglued just scares me.

Take care,

TJ
 
wouldn't hardened and polished tool steel reduce friction, you can also round off the top, that keeps it from snagging the belt splice and breaking it.
 
Guys: I have found glass to work better, because you don't get the heat build-up that will cause your steel plate to warp. Also, the steel plate will wear over time. Glass is cheaper, no fab time or cost, and when it breaks, you just knock it off with a hammer, scrape down the platen and glue on another piece. You can't beat it!

RJ Martin
 
i was lookin through mcmaster carr and found ultra high temp, machinable glass mica ceramic, max temp of 1472 degrees, high abrasion resistance, flexural strengh of 13,600 psi, what about that stuff? it's extremely expensive- 1/16"x 6"x 12" $380
 
here's another one for you- graphite max temp 5,000 degrees F. rockwell b-75 hardness. flexural strengh 6,000 psi. 1/4"x 12"x12"- $97
 
RJ-

What kind of glue do you use to attach it?

Do you use a ceramic belt to round the edges?

How long do you have to have it glued and clamped before you can grind on it?

Thanks,
Nick
 
RJ,

Thanks for the input. I will pass on the glass mica ceramic also. I am also interested in what you have found to be the best adhesive.
 
Guys: use Zap-a Gap, Green bottle. Put your platen arm in a vise with the platen horizontal. Apply the adhesive liberally, spread around with your finger. Slide the glass on and press gently down. You should have your glass cut about 1/4" wider than your platen. Spray the zap kicker liberally along the edges of the glass. the adhesive will cure from the edges in in about 1 minute. you can check cure by pressing lightly on the glass and watching one of the small bubbles that will undoubtedly have been trapped between the glass and the platen.
Of course, wipe things down with Acetone before you bond them.
MAKE SURE TO MOVE THE PLATEN backwards so that the belt rides smoothly over the top edge of the glass. you should do this all the time, regardless of having glass or not, because uneven belt tension or stretching the belt will NOT help you make things flat. NEW
Micron belts are the BEST for the final flatening operation. expect to use 1 belt per tang if you really want things flat. if you use worn belts, the edges will cut deeper than the center and your tang will be crowned up in the center. moving the tang from left to right as you grind will help you wear the belt out evenly.

RJ Martin
 
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