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Old 03-12-2019, 05:51 PM
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Default Inspecting used surface plates

How would you go about inspecting a used surface plate you were interested in buying?

What size is a good general size?
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Old 03-12-2019, 06:00 PM
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Make sure its flat
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Old 03-12-2019, 06:42 PM
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Granite, or cast iron?

Cast iron is basically worth scrap weight IMO.

Granite, there was a deal talked about here a few years ago for someone selling them online.

At this point, for what you are looking at doing, almost any granite surface plate would work for you.

I have a 12”x18” that I brought west with me, and that’s all I’ll really need at this point. I’ve used plates up to 6’ x 8’, both ‘shop’ and ‘inspection’ grade. The inspection of them is done these days with a laser, several points are checked for flatness across it’s surface. If it’s out of spec, a second plate is used to lap the face and bring it within spec.

Even with an abundance of use (1-2 shifts a day) in a toolroom setting, it would usually take a few years for a plate to require refacing, though they were checked yearly.


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Old 03-12-2019, 10:20 PM
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Quote:
Originally Posted by greywynd View Post
...At this point, for what you are looking at doing, almost any granite surface plate would work for you...
Yeah, unless you're doing a lot of very precise work I don't see the need for one. I've been machining on and off for well over 30 years and I've never had a surface plate--never had the need for one. If you can find a decent one cheap go for it but I wouldn't worry too much about getting one that was grade A or anything like that. You can buy 18" x 24" plates for less than 200 bucks depending on maker and grade.

You can check a surface plate with another surface plate or you can use a proven straight-edge. There are other methods but these two are common and doable by someone in a home shop. Lots of Youtube videos...
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Old 03-12-2019, 10:26 PM
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A granite plate that doesn't meet specs would make a good head stone.
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Old 03-13-2019, 02:50 AM
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For home small shop even think of the thicker counter top slabs .
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Old 03-13-2019, 10:09 AM
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I bought mine, when Grizzly was in Muncy, Pa, at about $.25/lb, then drove them home. In the catalog, it basically cost more to ship them, than the purchase price.
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Old 03-13-2019, 02:21 PM
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Quote:
Originally Posted by platypus20 View Post
I bought mine, when Grizzly was in Muncy, Pa, at about $.25/lb, then drove them home. In the catalog, it basically cost more to ship them, than the purchase price.
Grizzly also had an online sale several years ago. I think it was $40 shipped so I bought one, about 12 x 18 inches, probably not big enough for real shops.
The only real use I've had for it was checking the shaft that Old Man had in the Final Grinder when he sent it to me. It was bowed a few thousandths. That was very easy to spot on the plate.
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Old 03-13-2019, 02:34 PM
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It would be very easy to check if you have a camel back type of straight edge that has been scraped fat and straight. At least you would get a warn fuzzy feeling of it being flat. Check it from corner to corner with high spot blue or equivalent marking medium. That should tell you if it dips in the middle. Next, check it along the long length at say 4"-6" intervals, that should give you an idea of any other wear patterns on the plate.
Another way is to set the straight edge on 1-2-3 blocks and use a tenths reading indicator on a surface gage. Indicate from the surface plate to the underside of the straight edge. That's about as close you can do without taking it to someone that has the equipment to re-surface and re-calibrate a surface plate. KenS.
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Old 03-13-2019, 03:03 PM
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This is all I have needed so far, a 10" X 12" from Enco with free shipping
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