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Pitfalls of using the granite (NOT THE PART) as a Datum Alignment Feature

All,
I'm working on a project and remember seeing a tech article many years ago about the dangers of using the granite plate and not the part as a component of your part alignment. Does anyone have any idea where to find that article? Any help would be appreciated! Thank you, Erich
Parents
  • I have worked on some small 5-5-5 and 5-7-5 Brown & Sharp machines that had granite tables that were not part of the mechanicals of the machine. Those were actually calibrated and lapped as needed on an annual basis by our local surface plate calibration service. The annual CMM calibration was scheduled shortly after, just to make sure nothing 'moved' on the machine. It was nice because I could reliably use it as a datum simulator.

    I have also heard of some large gantry CMMs with plates that are moved in and out of the machine on rails like train cars. Those too could be calibrated. Really, it is just a bigger version of Wes' suggestion.
Reply
  • I have worked on some small 5-5-5 and 5-7-5 Brown & Sharp machines that had granite tables that were not part of the mechanicals of the machine. Those were actually calibrated and lapped as needed on an annual basis by our local surface plate calibration service. The annual CMM calibration was scheduled shortly after, just to make sure nothing 'moved' on the machine. It was nice because I could reliably use it as a datum simulator.

    I have also heard of some large gantry CMMs with plates that are moved in and out of the machine on rails like train cars. Those too could be calibrated. Really, it is just a bigger version of Wes' suggestion.
Children
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