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Thread: How flat does an Atoma need to be?

  1. #1
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    How flat does an Atoma need to be?

    I bought an Atoma #140 to use to flatten my Shapton Pro stones. It's not perfectly flat. Laying it diamond-face down onto my granite surface plate, the 0.0015" feeler gauge can slip under the middle of the Atoma without any resistance. The 0.0020" feeler gauge however drags just enough that the diamonds leave scratch marks on it even as it roughly slips past them. I interpert that to mean that the Atoma is hollow by somewhere between 0.0015" and 0.0020". Is that flat enough to flatten the Shaptons since every single thing I sharpened will, by proxy, be referenced against the Atoma?

    Thanks as usual.

  2. Believe it or not but a slightly convex stone makes it easier to keep your tools flat. A friend machined 2 aluminium plates for my Atoma 600 and 1200 to be slightly convex.

  3. #3
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    No way would I accept that for dressing my stones.
    Did you mean .020 it’s easy to add too many 0s
    Last edited by Andrew Hughes; 03-04-2019 at 6:17 PM.
    Aj

  4. #4
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    Quote Originally Posted by Andrew Hughes View Post
    No way would I accept that for dressing my stones.
    Did you mean .020 it’s easy to add too many 0s
    No, I meant what I wrote. Somewhere between 15 and 20 ten-thousandths of an inch.

  5. #5
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    Seems a touch excessive. Try flattening your stones and see how it works.
    Bumbling forward into the unknown.

  6. #6
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    Can you send it back?

    I bought the Atoma replacement sheets, and put them on a granite surface plate that stays on the drainboard of my sharpening sink. The plate came from Woodcraft, back when they sold the 9x12's several times a year for around 25 bucks. I didn't want a small stone to move around, and have running water on that sink with a double swivel spout that can cover a large area on the sink drainboard. It works fine for me.

    15 thousandths is the thickness of a matchbook cover. That, or more, sounds like way too much out of flat for this job, especially being concave.

    Back when we ground telescope mirrors, when I was in High School, it was much harder to make an optical flat, than any kind of curved surface mirror.

  7. #7
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    Quote Originally Posted by Ty Williams View Post
    No, I meant what I wrote. Somewhere between 15 and 20 ten-thousandths of an inch.
    Ok just making sure 15 ten thousands is pretty small number. So I change my stand it’s good.
    Curious how do you measure tenths?
    Aj

  8. #8
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    Oops. I missed the "ten" thousandth's. I was off by a factor of ten. My feeler gauges only measure in thousandths.

  9. #9
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    Quote Originally Posted by Tom M King View Post
    Oops. I missed the "ten" thousandth's. I was off by a factor of ten. My feeler gauges only measure in thousandths.
    Same here Tom.
    Im impressed he can measure in the 10ths that’s amazing
    Aj

  10. #10
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    To be fair, the feeler gauge set is in multiples of 5 tenths, not single tenths (and only that precisely up to 2 thousandths). I do have a dial indicator that reads in half tenths though (aka 5 one-hundred-thousandths). At that precision, you start worrying about temperature and how long you've touched the tool. You can put your finger against the thing and watch the dial wind as the heat from your hand changes the size of the thing.

  11. #11
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    Sounds great Ty.
    Have you seen Stanley’s Nano hones? Certain to satisfy the perfectionist


    https://nanohone.com/pages/about
    Aj

  12. #12
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    A dial test indicator?

    Tenths are probably not very useful in everyday woodworking, but can be useful in other aspects of the setup work. If you want something really flat you might be better off making your own plate and going from there, or doing what Tom does.
    Bumbling forward into the unknown.

  13. #13
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    Don’t trust the granite too much. My 3’x2’ granite was dished 4.5 microns in the middle, rather disappointing.
    ​You can do a lot with very little! You can do a little more with a lot!

  14. #14
    Quote Originally Posted by Ty Williams View Post
    No, I meant what I wrote. Somewhere between 15 and 20 ten-thousandths of an inch.
    That is really negligible. I would bet it will flatten your stones. At least adequately enough for the most fastidious woodworking shop.
    The deviation you are reporting is a little less than a THIRD of the thickness of a human hair.

  15. #15
    Quote Originally Posted by William Fretwell View Post
    Don’t trust the granite too much. My 3’x2’ granite was dished 4.5 microns in the middle, rather disappointing.
    4.5 microns? I don't think I'd be disappointed in that.......at least not for what I use a granite plate for.......Maybe you were being facetious, hard to tell on here. By my calcs, that's 2x flatter than an AA.
    *** "I have gained insights from many sources... experts, tradesman & novices.... no one has a monopoly on good ideas." Jim Dailey, SMC, Feb. 19, 2007
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