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Thread: plate glass ?
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13th Oct 2011, 10:56 PM #1
plate glass ?
I wonder if it is feasable to use plate glass ( instead of granite ) as a substitute precision level surface . I ask because I used to grind radio XTALS on plate glass . You shift the frequency buy removing a micron thin amount of quartz . Paste is used as you rub the thin quartz chip on the glass in a figure 8 . Another of my crackpot ideas Plate glass is optically flat . Mike
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13th Oct 2011, 11:06 PM #2
Hi Mike,
Short answer is no. Plate Glass isn't generally considered suitable. There have been numerous (sometimes heated) discussions on the use of Plate Glass for flattening and sharpening plane blades and chisels, on the woodworking forums.
Granite surface plates in small sizes are not all that expensive, Carbatec have one which is fair quality at a reasonable price.
Granite Surface Plate : CARBA-TEC
The problem with glass, as I recall, is that it flexes, even the fairly thick stuff, you would want it to be very thick (several inches I suspect) to avoid that, and normal quality (float manufactured) plate glass often has minute ripples in it.
That said, I think I remember reading that for a while during WW2 they were using thick ground glass surface plates just as a wartime emergency substitute.
Regards
Ray
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13th Oct 2011, 11:06 PM #3Most Valued Member
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Hi MM
oh boy you are opening a can of worms there.
Plate glass certainly isn't optically flat. Optical flats are optically flat. lol
Float glass is even less flat.
Having said that, it depends how flat the work piece is to start with and how flat you are trying to get it.
Given that a small granite plate runs $53.1 (on sale at carba-tec). I wouldnt play around with glass plates.
Stuart
p.s. optical flats are flatter than granite plates but generally much smaller and costlyLast edited by Stustoys; 13th Oct 2011 at 11:08 PM. Reason: p.s.
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13th Oct 2011, 11:18 PM #4
Hi Stuart,
We cross-posted, and said pretty much exactly the same thing, "Go ye forth to carbatec..."
Unless you want to sell that beautiful optical flat in the wooden box...
Regards
Ray
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13th Oct 2011, 11:29 PM #5
right
Hmmm good info. I have used plate glass for resurfacing carby parts , but in that case the tolerances are not that critical...up to a point. I noticed CDCO have a granite surface plate with a built in dial post ..but it would be too heavy for a flat rate box I would think . Mike
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13th Oct 2011, 11:48 PM #6Most Valued Member
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Hi Ray,
Did I mention that that was the small one? the large one is nice but not as nice. Maybe one day I'll need one lol
MM that CDCO plate is only 6"x6"x2" the carbtec ones are 300 x 230 x 50mm. They post them also for $21.18(well to 3153)
Stuart
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14th Oct 2011, 09:25 PM #7Most Valued Member
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Trouble with that plate is, it's too small to be particularly useful. IMO 600x400 is about the minimum useful size.
McJing has that size at $400 each IIRC. I think a granite plate is next on my 'must have' list as knowing how to scrape is pretty useless unless you have a known flat surface to test against.
PDW
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14th Oct 2011, 10:57 PM #8
Hi Peter,
Agree on size, bigger is always better ..
I got a 400 x 400 x 100 for $242 from this guy http://www.toolingonline.com.au/home...category_id=63
Freight was zero, since I picked it up. Otherwise it's freight cost for 55kg.
A good granite surface plate of any size is going to be flatter than plate glass...
Regards
RayLast edited by RayG; 14th Oct 2011 at 11:04 PM. Reason: elaboration..
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14th Oct 2011, 11:42 PM #9
+1 for plate glass: No; Granite: Yes
There's a reason the use of glass didn't survive the WWII emergency period.
I am again hoping to import a 900 X 600 plate for less than $500 total, but it is on the back burner right now as I'll be busy at work 20/7* until March or so.
*4 hours sleep...that should be enough, right?It's all part of the service here at The House of Pain™
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15th Oct 2011, 09:03 AM #10Distracted Member
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15th Oct 2011, 09:09 AM #11Most Valued Member
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McJING Tools Online
Dearer than your supplier but a bit bigger plate as an option as well. The reason I say 600mm minimum is, that way you can spot something like a 600mm straight edge across the diagonals. That's big enough for most jobs.
I'm going to have a chat with my foundry guy about the cost of some castings. I take Phil's point about them needing stress relieving etc but that's a lot easier than backyard iron casting.
PDW
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17th Oct 2011, 12:24 PM #12Intermediate Member
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Hi guys,
All this talk of granite flats has got me curious about whether it is all granite which is suitable or only granite with a special characteristic.
Just recently I set up my plate glass laying out table, so the topic is of some interest to me.
The reason for my question is a long time ago I was given a peice of granite bench top from a kithen install which is IIRC approx. 600 x 500 by roughly 1.5" thick.
Could I use that as a true flat, is there something I need to do to it to make it true or is that worth nothing more than a place to keep hot things off the main workbench?
Any advice will be appreciated.
Thanks
Cheers,
RossA
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17th Oct 2011, 01:07 PM #13Most Valued Member
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Hi RossA,
IIRC granites are different, pink granite has more quartz in it so wears better that black but deflects more than black granite.
A granite surface plate that size would be at least 75mm more likely 100mm thick. If you supported it on three points as a surface plate that size should be, I'd think it wouldn't be to hard to break it in two. Also the finish on a bench top is much more polished than a surface plate, it may not spot well(?)
As for how flat it is, that's anyone's guess. I think(others disagree) it depends what you are starting with and what you want to end up with. If you just want something "pretty flat" it might do the job. If you want to make a master square it almost certainly wont.
Stuart
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17th Oct 2011, 02:29 PM #14Most Valued Member
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I've got the piece cut out of our granite bench top. It''s only 20mm thick. Nicely polished but I haven't even bothered trying to check for flat, I know it's a waste of time.
There's no reason why, if you have enough patience and raw materials, that you can't lap 3 pieces of granite flat. This is just a refinement of what the telescope lens guys do when grinding a lens. They're aiming for a specific curvature, so are you. Yours is infinite...
I'd just spend the money.
PDW