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  1. #1
    Milacron's Avatar
    Milacron is online now Diamond
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    Ran across good buy on small Zeiss, year 1997 DCC CMM of about 20 x 20 travels with automatic probe changer that looks/works great except the idiots mucked up the table by dragging sharp heavy parts that put some pretty deep scratches in the granite surface. Table is integral to the slide so replacing just the granite would be nearly impossible and resurfacing it impractical.

    I would think it would be fine as is if one held the parts to be inspected in a jig/fixture, as long as that jig was always positioned in exactly the same spot on the plate surface...and/or referenced off a ball on the jig...but how many companies actually use one that way ?

  2. #2
    PBMW is offline Titanium
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    Correct me if I'm wrong, but when you inspect using a CMM you must first probe the part to establish a datum plane and XYZ zero. so , in reality, the table is only there to support the part and nothing more. It wouldn't matter to the CMM if the thing had a big hole out of it as long as that part didn't move during inspection
    Jim

  3. #3
    Milacron's Avatar
    Milacron is online now Diamond
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    I was thinking the same thing PB, but then I started thinking if that's the case then why do they have precision granite surfaces in the first place and trying to make some sense of how different companies might use them in that light. Could be that granite is simply the cheapest way to produce a relatively flat support surface. Friend of mine has a late Sheffield DCC CMM that appears to have aluminum or Moglice surface and he was saying "well, it's just a cheap model"....whaaa ?? (damn thing was still over $70,000)

  4. #4
    PBMW is offline Titanium
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    Ya know, CMM's are a strange animal. Sheffields used to have a steel table. And I have run enough of them to know that if I wanted to hide that little discrepant dimmension from you as you stand there looking over my shoulder. You'd never know that part was scrap.
    I've come to the conclusion that CMM's are really for customer piece of mind. "He's got a CMM...he must do good work." I think there may be some of that with the MFG's as well, because there is no real reason to have a granite plate as all these guys use error compensating software as well.
    They are just eye candy...
    (but I'm not gonna pass one up if I find a good deal on one...)
    Jim

  5. #5
    Milacron's Avatar
    Milacron is online now Diamond
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    I've come to the conclusion that CMM's are really for customer piece of mind.
    Probably mostly so...but handy for reverse engineering of complex parts I should think...don't need DCC for that however...manual would do fine...

  6. #6
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    bcstractor is offline Stainless
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    There are many parts over the years that I have designed that could only be inspected on a CMM. I don't know of any easy way to do some measurements by hand. It's pretty hard to find the diameter of a discontinuous surface on a plastic piece.

    Chris P

  7. #7
    damonfg is offline Titanium
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    So what level of accuracy can you hit with a Zeiss or the like?
    I do all my probing and reverse engineering on the VMC with the "pride of Renishaw".

  8. #8
    dkmc is offline Diamond
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    Wonder where the boss or owner was when they were plowing up the table...... :rolleyes:

    Edit:
    Oh, YES it's totally worthLESS.....
    I'll give you $500 for it out of sheer sympathy....

  9. #9
    Milacron's Avatar
    Milacron is online now Diamond
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    I'll give you $500 for it out of sheer sympathy....
    Do I have to give you the $25,000 worth of probes it comes with too ?

    Btw, I was walking by the decrepit Feeler lathe the other day and it was asking about you..."what happened to Dan...doesn't he like me ?? I really hate this humid climate and want to go north...HEY, mud dauber...SCAT !"

  10. #10
    PBMW is offline Titanium
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    Do I have to give you the $25,000 worth of probes it comes with too ?
    Why, Yes Don, Yes you do...

    Jim

  11. #11
    Tumbleweed Tim is offline Stainless
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    I am intrested. I got a piece of plywood I could use for the table. How much you gona ask?

  12. #12
    Milacron's Avatar
    Milacron is online now Diamond
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    got a piece of plywood I could use for the table
    Treated ? [img]smile.gif[/img] Dunno my sales price, haven't bought it yet...still "dickering" with owner...

    Guess I could spread out some spacklin in the cracks and spray paint it black...

    [img]smile.gif[/img]

  13. #13
    dkmc is offline Diamond
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    Do I have to give you the $25,000 worth of probes it comes with too ?
    Please??

    Oh, and can you retrofit it with that "Cheap-O" new software also, before you ship it here???
    PLEASE??


    Btw, I was walking by the decrepit Feeler lathe the other day
    Stand by, I'm still getting ready to get my Onmiturn on line, then I can send off a gloat....er.....comparison value for you to consider when you set your "best" price on it.

  14. #14
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    doug925 is offline Titanium
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    Treated ? Dunno my sales price, haven't bought it yet...still "dickering" with owner...

    Guess I could spread out some spacklin in the cracks and spray paint it black...
    Ahh hell, Al Babin is back!
    Now we know "the rest of the story" LOL
    Doug.

  15. #15
    jstolaruk is offline Senior Member
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    The beauty about granite for inspection purposes is its low temperature coefficent (5ppm/C); its high thermal inertia making it impervious to short term temperature fluctuations; and the ability to make a very flat surface.

    As far as this CMM goes, you're right, if the operator uses fixtures to stage parts, the granite top doesn't mean much. Unfortunately, a potential customer may wonder in his mind that if the previous owner was so lax in protecting the table, how was the rest of the machine treated.

  16. #16
    willbird is offline Banned
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    Man having a CMM handy is sure nice, I used to grind tapers in carbide and steel and it is a quick and accurate way of checking one. We were told to verify our work by two methods of measurement. Smaller tapers we poured slugs and used optical comparator to check them.

    Bill

  17. #17
    Hansdie's Avatar
    Hansdie is offline Hot Rolled
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    why do they have precision granite surfaces in the first place
    Who says its a "precision granite surface" many people assume thats it a traceable surface plate quality piece of granite. For the most part its not! Thats why you normally don't use the granite surface as a datum on a CMM.

  18. #18
    scojen is online now Stainless
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    Don,
    Pull the granite, send it out have it resurfaced, reinstall, Send it to me to dial it back in with the calibration program. Should not take more than 3 or 4 years (I'd only work on when I was bored have to have the right mind set ya know)to get it right then pay my way to S.C. put me up, feed me, it should only take a month or so to dial it back in on the show room floor then when you sell it elude to the customer after you get the check that it will cost him 30K for calibration at his site. What was I thinking that's your plan of attack.

    Scott

  19. #19
    metlmunchr is offline Diamond
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    Just getcha a piece of Granite looking Corian, slap it on top of what's there, and point out that it is equipped with the optional subplate

  20. #20
    willbird is offline Banned
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    They used to have the same people that lapped our granite surface plates also do the CMM

    Bill

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