Measuring an Untrue Radius - Metal Stamped and Formed Parts

J

jager

#1
I work with metal stamped and formed parts. I am having trouble measuring a radius which is untrue. I'm tracing the radius with our vision system. I can measure it 10 times and get 10 different readings depending where I start and end my points. Any suggestions?
I would appreciate any help!
Thank you
 
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Miner

Forum Moderator
Staff member
Admin
#2
Is changing the specification to a profile (rather than a radius) an option?

By definition, you cannot consistently measure a radius if the surface does not follow a consistent radius. Your results would be exactly what you are getting, namely a different radius dependent on where you measure.
 
J

jager

#3
It is a profile of surface 0.2, but the radius size would play into that. I could get a mylar overlay made to that radius size and location and see how close of a fit it is. I'll explain that I cannot measure the radius accurately.
Thank you
 

Michael_M

Trusted Information Resource
#4
Can your vision system place the overlay in place for you? Can you define the radius in the tolerances and give it a profile?

The vision system we use allows for the radii center point and size to be defined and then a profile called out.

If it matters, we just bought a MicroVu automatic (upgraded from the manual).
 
J

jager

#5
Ours is an OGP Avant Zip 400 from 1999. I don't think it will overlay for us. I'll look into that though. I was going to use the mylar overlay with our 30" comparator.
Thanks
 

Kingsld1

Involved In Discussions
#6
If you have less than 90 degrees of arc in a measured circle, you won't get very repeatable results. Any measurement error in an individual point in the measured circle gets amplified.

If you know where the center of the radius is supposed to be, you could move your origin to it, take points along the radius and report them as polar radius and polar angle.

This method would better fit for a profile measurement; i.e. every individual point has to fit within a defined zone versus a best fit circle.
 
J

jager

#7
Great idea. I'll try that. Thank you
Measuring radii on our formed parts is always a "get what you want" ordeal. Lots of arguments...
 

Proud Liberal

Quite Involved in Discussions
#8
See image from Y14.5 standard. Profile doesn't meet the requirement since the tolerance zone is crescent shaped. To accomplish your task, you can set a circular target on your OGP to the size of your USL and LSL, align to part, and capture images to prove to a customer that your PASS/FAIL evaluation is accurate (if he doesn't trust your report).
 

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