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  • Surface Plate

    I have a WW2 cast iron surface place that is 16" x 22".

    How can I tell if it is flat or not? I know there is some method to do this I think.

    John
    My Web Site

  • #2
    Use the search function.... Otherwise all that will happen in this thread is it will be derailed with many links to Shars, Starrett and dumpsters...
    Precision takes time.

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    • #3
      How flat do you need it? and what kind of tools/indicators do you have to work with?

      a good straight edge backlite with a bright light and some feeler gauges will let you check to within 2 or 3 thou.
      sweeping across the surface with a good .0005 indicator will get you within .001-.002.
      a thin coat of hi spot blue on another surface plate (as large or larger as the one your checking) will let you check
      the surface to the accuracy of the plate your using as a master.
      I cut it twice, and it's still too short!
      Scott

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      • #4
        The simplest way would be call a local machine shop or Community College that teaches machine shop and see if they have a CMM and can check it for you. They can print out a sheet showing the accuracy. If not drive up to "The Cape" and contact Barks Equipment as they have a surface plate and scrape, so they will know how to blue it up and measure it for you. I taught a scraping seminar there and helped rebuilt some crank shaft grinders for them. Or use the method the guy before me said.

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        • #5
          Or just use a laser, I think it was Evan who had the page about using one?
          Amount of experience is in direct proportion to the value of broken equipment.

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          • #6
            I don't have much to work with except a real nice 8" machine level that has 0.0005IN/10IN marked on it. The bottom is scraped and has a V in the middle with two flat edges. And I have a buddy that lives in the next town that just got a new portable CMM... hmm options.

            How flat do I need it, well I don't know. I just got the scraping issues and I have a compound on the Samson that is in need of some scraping for sure.

            A laser?

            Thanks
            John
            My Web Site

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            • #7
              I think I would use your level as a straight edge to check it out, if it looks pretty good that way,
              have your buddy with the CMM check it. Just guessing, but I think it'll probably need some work
              for what you want to use it for, unless it was very well cared for for the last 65 yr.
              I cut it twice, and it's still too short!
              Scott

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              • #8
                Check it against a "known" (ie calibrated) - or "looks good" other larger surface plate in several orientations - using "blue" in the first instance.

                If the "blue" "looks good" - gp ahead and use the plate for its intended purpose.

                If it looks "bad" or "not too good" then use your level and/or feeler gauges if needed to try to quantify any error/s (if any). If within reason - use the plate - if not, don't use it.

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                • #9
                  Don't have access to a known good surface plate...

                  It looks fairly good, I got it from a retired shop teacher that had a whole machine shop in his basement.

                  John
                  My Web Site

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                  • #10
                    If it has that sort of a history and looks good too, I'd say it is quite safe to use assuming it to be within calibration limits - even a "Class D" ("shop" grade) should be nore than good enough.

                    Get going!!

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                    • #11
                      Here is the laser stuff that you can do quite cheaply: http://www.cnccookbook.com/MTLaserMetrology.htm

                      It doesn't necessarily tell you how much off you are, but at least you know if it is way off.
                      Amount of experience is in direct proportion to the value of broken equipment.

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                      • #12
                        That laser flatness set-up was invented and reported by Evan.

                        It would have been nice if the owner of CNC Cook Book had given credit to Evan for it.

                        I link to Evan's thread about it would have been nice as well.

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                        • #13
                          Originally posted by Jaakko Fagerlund View Post
                          Here is the laser stuff that you can do quite cheaply: http://www.cnccookbook.com/MTLaserMetrology.htm

                          It doesn't necessarily tell you how much off you are, but at least you know if it is way off.
                          I found Evan's thread on laser level the link is a verbatim copy of the thread. Credit to Evan should have been included, I see he included a link to the thread right in the first line. He did add a bit to the information...

                          In any case I have all the tools to do that test so that is a place to begin.

                          John
                          Last edited by BigJohnT; 12-11-2012, 06:46 AM.
                          My Web Site

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                          • #14
                            If you actually care if the thing is really "flat", then you can't assume anything, and need to use some accurate method to check.

                            If it only needs to be 'close", you can check with a straight edge, like the edge of a a decent rule. If you ask some of us, we would want it to tenths as a reference, and that may not be what you need, so don't listen very hard unless you want that. You are probably starting out the right way with a "sanity check".
                            1601

                            Keep eye on ball.
                            Hashim Khan

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                            • #15
                              Yea, if it passes the sanity check then it is worth hauling over to Dexter for closer inspection on the CMM.

                              BTW, what part of MO are you in?

                              John
                              My Web Site

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