Straightness

[[Cl...]]

I have a diameter straightness (.0004) callout on a cylinder that is < than .500" in length,
any suggestions on the best way to measure this? Wouldn't cylindricity be more appropriate?

[[Ow...]]

I think that would depend on what other GD&T might be applied.
If diameter and roundness of the cylinder isn't controlled, several circles throughout the length recalled into a 3D-line would probably be sufficient.However, if diameter and roundness are controlled, I'd use cylindricity but, I guess if the characteristic has to match the print, so be it.
Seems like a lot of older drawings use straightness and circularity to control a cylinder where newer drawings just use cylindricity. Cylindricity controls straightness, roundness and to a degree taper.

[[Er...]]

Is the reqirement on the axis of the cylinder or the surface?
The reason for asking is, there is a method that can be used for measuring straightness that "eliminates" the machine error of one axis. But I dont think that can be used if the axis is toleranced.

[[Br...]]

If the leader for the straightness tolerance points to the surface of the feature, then it applies to each longitudinal element of the surface. This is similar to Cylindricity I suppose, but Cylindricity applies to the entire surface at the same time. The tolerance zone is made up of two concentric cylinders. With straightness applied to the surface of a cylinder, the tolerance zone is made up of two parallel lines. Worst case scenario-If it fails as Cylindricity, It might still be ok in a straightness tolerance. But if you have to make it match the drawing, you'll have to measure lines on the cylinder.

Now if the Straightness FCF is shown attached to the size dimension with a diameter symbol in front of the tolerance, then the straightness applies to the derived median line. In this case, just measure the cylinder and report it as a straightness characteristic.

[[Cl...]]

"Now if the Straightness FCF is shown attached to the size dimension with a diameter symbol in front of the tolerance, then the straightness applies to the derived median line. In this case, just measure the cylinder and report it as a straightness characteristic."

Yes, this is the way it's called out.

[[Da...]]

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Clarke, do you have a similar case like this one? -> https://youtu.be/-DtzspjcRKI?t=327

[[Cl...]]

Nope, the callout is;

straightness - diameter - .0004 @MMC

[[Br...]]

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Then all you have to do is measure a Cylinder and report it as a straightness characteristic. I'm not sure if Calypso supports MMC with straightness. You'll have to try it to find out. As far as the best strategy, probably linear line paths so you get a lot of data along the length of the part.