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True position or concentricity


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Question to the experts. I have a part 170mm long 6.00mm Ø (some areas smaller).
The customer drawing calls out true position at various locations on the shaft, but are
open to changes because of bad repeatability from a previous program strategy.

The only datum is -A- which is the 6.00mm OD. The tip of the part is split down the middle
lengthwise for 25.00mm and they want it's position as well.
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Use the centerline of the split as datum B and the end of the shaft as C. Check all cylinders that are .600 and recall them into a cylinder for A. Also check the A cylinders for coaxiality.
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This should be simple, but I'm not sure that true position is the right way to
evaluate this?Concentricity, runout? I do not know the function of the tool.

All diameters and slot true position to -A- no MMC/LMC modifiers.
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True position will give you the same answer as concentricity. For ISO and in Calypso, concentricity is just a special case of position in which both features share the same axis. David is spot on about making your Datum A as long as possible. You want to eliminate as much projection error as possible.

Concentricity was obsoleted in the latest Y14.5 release in favor of position or runout.
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.
Clarke,

I'd recommend the DRF mentioned above with runout as the characteristic to control the feature of interest. Runout controls form, orientation and location. You can simultaneously evaluate wobble, roundness issues and axis offset. Runout works great not just for rotating parts but any coaxial features of size.


Jeff Frodermann
Meier Tool & Engineering
Anoka, Minnesota
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You know it!
However, what about Coaxiality which uses the same symbol?
Seems like most newer prints I work with just use non-fully defined profile characteristics on 80-90% of everything...smh
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