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Truing Up Starrett 8" Level

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  • #16
    ENL, that's great info and clears up the issue of why there MIGHT be some concavity. But all in all I can't see us home shop types investing in a SET of Starret levels to cover all the situations.

    In a way I almost like the Lufkin approach better. Then if the user needs something as a bridge it's up to them to use something like a parallel to extend the spots being checked and the user knows what they are up against.
    Chilliwack BC, Canada

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    • #17
      Originally posted by enl View Post
      Checked my 8" Starrett 98. The center is at most 10 micon (well under a tenth) high on the flat. At this precision, there is no measurable variation across the flat.

      By my reading of the standards that I have access to (company standards to meet assorted MILspecs), it is not to be convex. The manufacturer will then insure that any error is in the direction on concavity to meet this, but (in what I have access to), there is no requirement about how concave. Only that it not be convex.

      It is also specified that the level used should not be longer than needed to span the surface being leveled, which would preclude using an 18" level to cross level a lathe with 10" between the ways, but the 18" would be fine to level it along the ways, presuming they are longer than that.
      I would imagine since the levels are sprung or pressed as the tech from Starrett described to me to make the bottom convex there would be a lot of variation in each level produced. I'll bet if you were to check another one you would find it's different but as long as there is some concavity to the bottom it's OK. The tech guy told me that in the production of these they don't have time to screw around with each one, so it's sounds like it would be a slam bang operation. Put X amount of pressure to the center and if you end up -.0001 to - .003 you'r good to go.

      JL..............

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      • #18
        Yes, these levels are supposed to be slightly concave. I've read about .0002" high in the center, but I'm not positive. The idea is that having the center hollow they can last longer before they start to rock.

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        • #19
          I really QUESTION that tech's response. These levels are supposed to be precision devices. And they are made of cast iron. And the bottoms are supposed to be flat at the ends, flat and in the same plane. Pressing etc will add stresses to the material, leading to the potential for relaxation, etc, especially as the castings are machined, and so might relieve stresses and cause warpage.

          So, if that is done at all, and I see no reason for them to do that, it must be done before the bottoms are ground. And hopefully before stress relieving the castings.

          It would seem far better to simply hit the middle area with a grinding operation, possibly at a large radius in a fixture, prior to final grinding of the bottoms. That would be more predictable, and far less crude.

          If one re-scrapes the bottom of a level, which is quite easy to do, as it is a planar surface, then it i sufficient to do a few extra passes of scraping in the middle. If one knows one's removal rate, which is often around 2 tenths per fairly heavy pass, then a couple passes could be enough.
          CNC machines only go through the motions

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          • #20
            I should not be surprised if every one is different. Mine is moderately well used, so the ends likely have some wear, but there is no clear wear edge between the end sections and the center section. I have no idea what the original concavity was, nor if there is a precise spec. Only that the specs I have, which are written to meet standards I don't have in hand, don't specify how much. Never really thought about how to do it, as I purchase and use, not make, them.

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            • #21
              Originally posted by JoeLee View Post
              I always thought it was .005 in 12".

              JL...............
              I'm not sure what model you have, but most Starretts of that persuasion use a 10" metric which is not unhandy.
              Last I bought a handful, they were ~$70, so not worth fussiness (in that place & time).
              Discrepancy Vee to flat, whether truly flat or not, was well within the class of work they were used for.
              There are debates re: whether levels should be flat or "hollow"...my Scherr-Tumico master level @ .0005"/12" came flat and is maintained so.

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              • #22
                To add to the confusion, I have several Starrett 98 levels, two are 12", holding them base to base shows no light in the center, they are used, in reasonably good condition showing normal use and no signs of modification. There is no sign of rocking either.

                They both have a grooved base, but neither has a true Vee grooove. One has a round groove as cut by a ball end mill. On the other, the sides of the vee are not flat but convex. My 8" 98 has a similar convex Vee.

                The level with the round groove is an older unit, finished in gloss black enamel, not the usual matte finish.

                I have another 6" similar level byExact Level & tool Co. that some clever fellow has engraved "machine repair" on one of the Vee flats with a vibrating pencil.
                Jim H.

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                • #23
                  The usual relief is a couple tenths, if it is relieved at all. Not sure you would see any light with that across the width of the level base. I scraped mine flat.

                  Remember, flat" is within the spec of "not convex". Could just as well be ground flat straight across.
                  CNC machines only go through the motions

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                  • #24
                    "Not sure you would see any light with that across the width of the level base."

                    Since Starrett tools are part of this thread, I recall seeing their test for squares was whether they block light in the test rig. A couple tenths is obvious.
                    Whether that is so across the width of a level at 12x + thickness, maybe not.

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                    • #25
                      Just put a new sheet of 400 paper on your surface plate and give it a few rubs longitudinally and Bobs your uncle.

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                      • #26
                        Originally posted by Carm View Post
                        "Not sure you would see any light with that across the width of the level base."

                        Since Starrett tools are part of this thread, I recall seeing their test for squares was whether they block light in the test rig. A couple tenths is obvious.
                        Whether that is so across the width of a level at 12x + thickness, maybe not.
                        That's usually with a "knife edge" square, I think or possibly with cylinder squares.
                        Last edited by J Tiers; 10-28-2016, 06:24 PM.
                        CNC machines only go through the motions

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