hexagon logo
Register Sign in
  • Replies 20 replies
  • Subscribers 227 subscribers
  • Views 275 views
  • Users 0 members are here
Options
Related

Datum Shift

cmm-measurer
ConfusedI received a report from a vendor where they are showing everything on a part 100% in tolerance. I have checked the part myself and show quite a few things out of tolerance. On their report I noticed a term "DATUM SHIFT" and some variables "X,Y,Z", etc. just before each dimension is reported. My question is this, What exactly is "DATUM SHIFT" and what is it doing? Is there some kind of data manipulation going on here?
Parents
  • In general terms:


    Datum Shift is a sort of "best fit" that is either trying to mimick a hard gage or account for a material condition modifer on a datum. At least those are the ways it should be used. You are correct in suspecting that it can also be used to made bad parts look good.



    As to how how it can effect a group of holes to each other well it could be good or it could be bad there is no way to tell from the information you have provided, but the more important question is do you care? If the holes aren't toleranced to each other you can't hold someone to that standard if it's not on the print. All you can do is hope that whoever designed the part took all of that into account when they toleranced the part.

    As wscmm said:

    just remember ALL the holes on your part have to be moved the same amount and will be part of your TP calculation. You can't move 1 hole one way and then another hole the opposite directions to make it in tolerance.

    But again based on what you have given us we can't answer that. To paraphrase Wes, if you want more you have to give us more. Until then all you will get is GIGO. And in that vein I think that chromatically the parts are noncompliant and should be rejected on that basis.
Reply
  • In general terms:


    Datum Shift is a sort of "best fit" that is either trying to mimick a hard gage or account for a material condition modifer on a datum. At least those are the ways it should be used. You are correct in suspecting that it can also be used to made bad parts look good.



    As to how how it can effect a group of holes to each other well it could be good or it could be bad there is no way to tell from the information you have provided, but the more important question is do you care? If the holes aren't toleranced to each other you can't hold someone to that standard if it's not on the print. All you can do is hope that whoever designed the part took all of that into account when they toleranced the part.

    As wscmm said:

    just remember ALL the holes on your part have to be moved the same amount and will be part of your TP calculation. You can't move 1 hole one way and then another hole the opposite directions to make it in tolerance.

    But again based on what you have given us we can't answer that. To paraphrase Wes, if you want more you have to give us more. Until then all you will get is GIGO. And in that vein I think that chromatically the parts are noncompliant and should be rejected on that basis.
Children
No Data
© 2024 Hexagon AB and/or its subsidiaries. Privacy Policy | Cloud Services Agreement