PolyWorks: GD&T Concentricity

This PolyWorks training video will explain how to use Concentricity of measured cylindrical data. This is useful for understanding the GD&T callout Concentricity and how to apply it to a machined product.
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[@faizanabrar6636]

Hi
What was the plane of projection for the two cylinders.
We’re they the same or different
Also how to locate in which direction is the drift - if possible to rectify by machining

[@diversedimensions1]

Hey there, Faizan. So good to hear from you and thanks for reaching out. What is your email address that I can reply to?

[@anantghatkar2008]

Hello Sir...pls let me know if this method give a reliable result.
Currently we are stuck in the same.
If we measure coaxiality of one cylinder with respect to other...it show x value.
And if we measure vice versa..the results are way different.
We have half inch axis length .......needed to be coaxial with another half inch axis ..... separated by 4 inch . The dia of cylinder is 1 inch.
Both the cylinders are done in one setting from one direction.

[@diversedimensions1]

Thanks Anant! Can you send me your workspace? [e-mail] I will take a look and give you some ideas.

[@anantghatkar2008]

@@diversedimensions1 Sir I am sending you a photo of job. Which we have mfgd. And I have indicated the cylinders and axis.

[@joshhines2388]

Did the customer agree with your 0.011" concentricity? This is a pretty classic example of where not to use it.

[@diversedimensions1]

Hey there, Josh. The client was holding tighter tolerances but this was a video showing theory and approach to the data capture using the laser tracker.

[@jonathanbatson6541]

@@diversedimensions1 Good points. Your method is spot on. The reason we/you are seeing such a large number is due to the measurement uncertainty and trig. Design engineers do this often without consideration of how small/short the axis is and how far the other bore is from the datum. A 0.0008" form error over 1" axis length projected over 10" means 0.008" off center at that 10". I run into this allot and commonly subject using cylindricity across both bores and making them both the datum.
Anyways, good video and keep sharing the info. our industry needs to talk more about these things

[@diversedimensions1]

@@jonathanbatson6541 Thanks so much for the reply here, Jonathan. Totally correct on the geometry effect here. It is always a good conversation on where and when to use concentricity

[@spencercampbell8396]

@@diversedimensions1 So what would be some examples of a good time to use it? We use a laser tracker a lot for setting up and inspection of large repair parts, which most of the time require bores to be in alignment across relatively large distances.

[@diversedimensions1]

@@spencercampbell8396 Hey there, Spencer. Thanks for reaching out and I would be interested in checking your drawing out and seeing what you guys are getting into with concentricity with your tracker. What is a good email address for you? I will reach out and maybe we can schedule a Zoom or a Teams visit.

[@inderjeetsingh4231]

Hi...recently i used this method to check concentricity....two coaxial cylinder were 19.8 and 19.6 from a plane having nomial dim 19.8 plus minus 0.3...but it shows concetricity of 1 mm...how is this possible

[@diversedimensions1]

Thanks for sending this reply over, Inderjeet. Can you send over your compressed workspace? I will take a look.

[@inderjeetsingh4231]

@@diversedimensions1 yes.. sure..plz share your email id

[@diversedimensions1]

@@inderjeetsingh4231 [e-mail]

[@inderjeetsingh4231]

@@diversedimensions1 thankeww soo much

[@jonathanbatson6541]

The reason we/you are seeing such a large number is due to the measurement uncertainty and trig. Design engineers do this often without consideration of how small/short the axis is and how far the other bore is from the datum. A 0.0008" form error over 1" axis length projected over 10" means 0.008" off center at that 10". I run into this allot and commonly subject using cylindricity across both bores and making them both the datum.