×
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

Measuring straightness

Measuring straightness

Measuring straightness

(OP)
I have a straight edge approximately 38mm long by 20mm wide and 1mm thick. The straight edge is bevelled both sides and is believed to be better than +/- 3 microns for straightness (overall).

Can anyone suggest how to measure the straightness to substantially better than 1 micron both for the overall length and over shorter distances of approximately 3mm?

RE: Measuring straightness

3D metrology I suppose

Cyril Guichard
Mechanical Engineer Consultant
France

RE: Measuring straightness

(OP)
In my experience a 3D metrology machine will not be anywhere near accurate enough although the principle is probably correct.

RE: Measuring straightness

Perhaps try contacting the "standards bureau" of your country, perhaps also called "measurements bureau"?

These are the agencies responsible for maintaining the "standard" units for length, weights, volumnes, etc.

"Do not worry about your problems with mathematics, I assure you mine are far greater."   
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

RE: Measuring straightness

You might be able to configure a surface profilometer to run down the edge with a modified probe.  Something like a Dektak:
http://www.veeco.com/appnotes/AN525%20_Dektak_Surface.pdf

Don't remember if Wyko makes a physical contact profilometer, though.

TTFN



RE: Measuring straightness

There are coordinate measuring machines that have sufficient accuracy to do what you want.  There are commercial measuring services, so you don't have to buy a machine.  Probably Mitutoyo, Zeiss, Leitz, and SIP at a minimum would make machines that could do it.

A distance-measuring interfereometer (DMI) with straightness optics could perhaps suffice, something like a Renishaw ML10.  You'd have to work out a way to guide it.

If you're using it as a straightness reference for metrology in a horizontal plane, you can always use straightedge reversal to null the straightedge error, so it would already be good enough

RE: Measuring straightness

I am having a hard time picturing the part.  If there is a flat face at the edge with a highly polished finish, it might be possible to check the flatness using an optical flat and a monochromatic light of the type used to evaluate the flatness of mechanical seal faces.  That would give a visual indication of flatness within 1 helium light band or about 0.3 microns.  Of course, if it comes to a knife edge, this will not work.  Otherwise, mechanical seal manufacturers use coordiate mapping equipment that can provide a seal face profile accurate to a fraction of a helium light band. If you contacted a major mechanical seal manufacturer, they might be able to help direct you to a suitable machine.

RE: Measuring straightness

I doubt you can hold that ruler straight to one micron.

Mike Halloran
Pembroke Pines, FL, USA

RE: Measuring straightness

The Dektak profilometer can measure surface roughness over several inches

TTFN



RE: Measuring straightness

Laser, it follows a true straight path.  Dial it in with a scope on the recieving end.

Well, true being straight means in the absence of high gravitational field, which I think you would qualify.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

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