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expressline99 said:
Bob, Shars says they can provide a NIST traceable plate for an extra $75.00 would this fit the bill? If not I'm about to buy a new one from either ACE, Standridge, or perhaps Precision.
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Paul, it is not so much the NIST certification, which can be pencil whipped very easily. This is an item that you cannot test yourself. Pick people you can trust. If you get a used one, get it certified after purchase by well regarded pros. It is a reference surface, that your work, tools, tooling, and scraping will count on to be what it says it is. I am a really frugal guy, always looking for a better deal, but I don't want to be second guessing if my surface plate is adequately flat or not. Contrary to hearsay and advice in this thread, you cannot tell if a surface plate is suitably accurate or not with what we typically have in our modest shops. If someone does not care, then fine, go for it. Just know that you are constantly guessing. On layout work and other lower accuracy work, it does not matter. For setting a sandwich and a cup of coffee on , it does not matter. On a precision scraping job or machine rehab, it does matter. For metrology work, it does matter. For testing your tools and tooling, it does matter.
 
Let me add my vote to what Bob has said. There are only a few items in your shop that have to be fully trustworthy - things that are very difficult to verify, but used as a reference for everything else. Surface plate, cylindrical square or granite square and your gauge blocks are the best examples of this. You can check everything else in your shop with these and a good test indicator.

If you surface plate is in question then I can't imagine how to calibrate everything else.
 
Dabbler said:
Let me add my vote to what Bob has said. There are only a few items in your shop that have to be fully trustworthy - things that are very difficult to verify, but used as a reference for everything else. Surface plate, cylindrical square or granite square and your gauge blocks are the best examples of this. You can check everything else in your shop with these and a good test indicator.

If you surface plate is in question then I can't imagine how to calibrate everything else.
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I'm taking action on this right now. Should have the decision made tomorrow. :) Then we can move on to using it to scrape in a home made straight edge.
 
expressline99 said:
OK I bought a new Standridge 24x24x3 Grade A. Hopefully I'll get it delivered next week. If that isn't good enough I don't know what else to do.
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Good choice, Paul. It is certainly good enough. AA is for temperature controlled metrology labs, not for home shops. AA will of course work fine, but is simply not needed in a home shop
 
Paul, here is the Federal standard for surface plates:
http://standridgegranite.com/forms/fed-spec-ggg-p-463c
The area that describes flatness is section 3.3.4. For a 24x24" plate, the maximum deviation tolerance over the entire plate is 150 microinches, which is .00015". "150 millionths" sounds even better. ;) Grade B is double that, grade AA is half of that. If Standridge does the same quality of work in their shop that their road service guys did on ours, the plate they send you will be calibrated to AA tolerance. They deliver more than they promise. Having been made and calibrated in their factory, with higher end test equipment available, I think exceeding the specs is likely. Standridge is a class act company in a business where reputation is everything. Manufacturers and high end shops depend on Standridge, their reputations matter as well, and returned work for out of tolerance is a black mark. In our hobby shops, we just smile and rest easy because we trust that they have done their work correctly and tested it thoroughly.

Make sure that you set the plate up according to the instructions. It will be best installed where sunlight through a window does not shine on it, and in an area with minimum temperature variations. Just do the best you can with what you have...
http://standridgegranite.com/forms/installation-instructions
 
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My plate arrived today at my warehouse. So it's sitting there in a crate waiting to be unpacked. But I have to build the stand now.
 
Your plate being 24 x 24" will give you diagonals just under 34". You should be able to spot in a 30" straightedge on your new plate on the diagonals. Ideally a lathe bed is tested and marked with a straightedge longer than the bed by a few inches. It is possible to do it with a shorter straightedge and doing overlapping work, but you will need to get up to speed on doing that. But that is well down the road. Other than that, your surface plate should do just about everything you need it to. Congratulations! I would have had to open it and look at it and rub it gently... :)
 
Bob Korves said:
Your plate being 24 x 24" will give you diagonals just under 34". You should be able to spot in a 30" straightedge on your new plate on the diagonals. Ideally a lathe bed is tested and marked with a straightedge longer than the bed by a few inches. It is possible to do it with a shorter straightedge and doing overlapping work, but you will need to get up to speed on doing that. But that is well down the road. Other than that, your surface plate should do just about everything you need it to. Congratulations! I would have had to open it and look at it and rub it gently... :)
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I had to move it with the forklift twice. I was very gentle. Exciting times! Hopefully I can pickup the 2" square tubing this week! I moved my table saw out of the garage last weekend to make room for the plate to live. The overlap should be interesting. But I have to make it through having the bed level...

ah I almost forgot the new lathe legs are painted now. So more work towards the chip pan.
The bed is 7" wide at the most. 5" between centers of the vees. So what size of level will I need. Getting closer to being able to scrape something! :)
 
expressline99 said:
The bed is 7" wide at the most. 5" between centers of the vees. So what size of level will I need. Getting closer to being able to scrape something!
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Wide enough to reach across the ways to level them. I would not buy one longer than that, the length will be in the way on other jobs. Trusted (that means tested) parallels can be used to bridge longer work.
 
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