Glass platen attachment

[va-banjopicker]

When you attache the glass to the platen Do you need to rough up the back side of the glass to give it some tooth?

[boatbuilder]

I've never roughed up the glass but my steel platen is surface ground with 120 grit finish. I have had no problems with it holding on.
Jim

[B.Finnigan]

I use precision ground and heat treated O1. To get it dead flat I use a granite slab and sand paper. With hardened steel you drill and tap it to the grinder platen and can easily replace it. I really don't want to think about what would happen if that glass came loose. four drilled and tapped 14-20 bolts is far better insurance IMHO.

[Ed Caffrey]

I use mild steel (5/16" thick) for glass platens.....I "rough" the steel with a couple of passes on the surface grinder @ 50 grit, then CLEAN the glass good with acetone/windex. Lately I've taken to welding a small "shelf" at the bottom to support the glass...just in case it ever comes loose. This has only happened to me once....when I was dumb enough to try using double sided carpet tape....it was a mess, and the Mrs. was picking glass fragments out out of my face for a couple of days.

I've never had the glass come loose since using acraglass.

[Karl B. Andersen]

I also weld a small ledge on the bottom for insurance.
I mount with exterior mounting tape - too easy not to.
When I replace the platen - which is necessary every couple years - the only way to get it off is in itty, bitty pieces.

[Ed Caffrey]

Karl mentioned something that made me think..... it's true that the glass will eventually need to be replaced....there was a time when I also removed it in "itty, bitty" pieces....what I do now is removed the platen (mine is held in place with 2, 1/4-20 bolts) open up the bench vise jaws wide, lay the platen across the open jaws, and run a propane torch back and forth along the back/under side until the acraglass "let's go". (the glass generally comes off in one piece) Then I let it cool, throw it in the blast cabinet, clean it, then apply a light coat of acraglass, and a new piece of "glass". I use just a couple of pony clamps to hold things in place, and let it sit overnight.....back in business!

[grant]

I used JB-weld on mine. I heard that carburetor cleaner will remove that after an overnight soak.

[Dave Armour]

I hate to ask a really stupid question, but what is the purpose of making a platen out of glass? I just got a 2x72 2 weeks ago, so it's quite a learning curve from my delta 1x30.

[B.Finnigan]

I asked the same question at least in regards to using glass.

It gives you a very flat smooth surface and very sharp edges to get a crisp clean grind on the ricasso. But as I mentioned above heat treated and low temp tempering a 1/4" PC O1 does the same and with a few more advantages then glass.

But way back a couple high profile knife makers started using glass backed platens and everyone else just went right along and never considered other options. Many years ago when I bought my chunk of O1 it was $7 and I still had enough for another project. Back then getting glass and getting it cut to your platen dimensions was much more expensive. I never saw any reason to use glass. But everyone else just went with the flow. My O1 platen is still smooth and symmetrical and real easy to replace.

It still has the sanding marks from when I ran it across sandpaper on my granite stone. And I still occasionally cut a knuckle or two on the edges when I'm swapping out a belt.

[Ed Caffrey]

I hate to ask a really stupid question, but what is the purpose of making a platen out of glass?

Not a stupid question at all! Until I tried it, I couldn't figure out what all the hype was about either..... the two things that I found most attractive about it are...

1. MUCH less heat build-up.....this provides a whole list of benefits, not the least of which is longer belt life, less belt glazing, and less burn hazard for me.

2. I didn't want to believe it at first, but there is a night and day difference in how my grinds looked.....a 120 grit finish looks like a 220, a 220 like a 400 and so on compared to a metal/steel platen.

Will it make a person a "better" grinder? No. Will it magically transform a person from unskilled to skilled? No. But the list of benefits are very tangible and real.

I resisted it for a long time, but once I went with a glass face on my platen, I very much liked it, and will continue to use it.

[Karl B. Andersen]

And keep in mind that it's not just "glass"- it's pyroceramic which is really not a "glass" but a transparent ceramic.
Ceramic that's been heat treated to withstand "thermal shock and any application where high temperature tolerance is required."
If you simply use a piece of window glass, you'll be in trouble.
What we use is often used in wood, coal and pellet stove doors.