×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

how to establish datums at MMB using CMM

how to establish datums at MMB using CMM

how to establish datums at MMB using CMM

(OP)
Hi,
A very simple question but I don't have answer. Let's take fig. 4-18 in '09 standard as an example. I have a hard gage simulating datam A, B and C. If I use CMM to inspect all gd&t, do I establish datums by probing surfaces on actual part or datum feature simulators on gage?
If the latter approach, how do I achieve good R&R? I mean you can't repeat the datum shift that other inspector gets during his inspection process.

Thanks in advance.

RE: how to establish datums at MMB using CMM

bxbzq,

You could establish the datums and DRF either by probing the gage surfaces or the actual part surfaces. In theory, the result should be the same either way.

In reality, it is very difficult to get the same result either way. If you probe the gage surfaces, the DRF is easy to set up but then you are allowed to shift the part around on the gage. If you probe the part surfaces, the DRF is difficult to set up because the software must perform "soft gage" calculations. Most software is not able to do this, at least with the default functionality.

In order to achieve good R&R, you would need to find the "optimal" datum shift. This would be the shift that results in the smallest measured value for the position tolerance.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: how to establish datums at MMB using CMM

Here is an older thread that discussed a similar question:

Link

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources