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!

*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.


Material Choice for CMM Fixture

Material Choice for CMM Fixture

I'm designing a fixture to elevate the qualification sphere on our CMM table by 6". The fixture does not need to repeat position with high accuracy, but it does need to be dimensionally stable during the probe qualification routine (up to about 6 hours). The temperature in the lab may vary within a range of about 5 degrees F. I need the position of the sphere, once located, to vary by less than .0001" due to environmental factors.

What material would you choose to be both stable and affordable?

RE: Material Choice for CMM Fixture

Stable & affordable.

Hmm, when we care about thermal stability (drift as we normally call it) and can't somehow control the temperature of the piece then we use materials like Invar or Super Invar but they aint cheap. Zerodur is even fancier.

I'd calculate the max rate you can handle based on desired max total drift & the temperature delta then look at a table like this and see what might work:

Posting guidelines FAQ731-376: Forum Policies (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Material Choice for CMM Fixture

Thanks for the link, KENAT. According to those resources, I'm looking for a material with a CTE of about 3 (10-6 in/(in R)). Looks like I've been overthinking the problem; I can just place my qualification sphere on top of a brick! tongue

RE: Material Choice for CMM Fixture

You may get away with granite, while it's nominal thermal coefficient is a bit higher than you'd like, reality is being a big monolithic mass it will have a fairly low time constant.

So if you're worried about relatively short term fluctuations it may be fine, if you have a long term thermal gradient though you may have an issue.

Posting guidelines FAQ731-376: Forum Policies (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

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!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close