why are bigger balls more accurate?

[[Pa...]]

1) Can anyone explain in a sentence or two why bigger probing spheres are more accurate than smaller spheres?
And also:
2) Why is locating your artifact near the position where you will actually measure your part more accurate than locating the sphere at the far end of the table?
In both cases, I sort of understand why, but I can't clearly explain why, in which case I don't really understand it.
PaulS

[[An...]]

See attached.

Contribution_20_04_2020.pdf

[[SH...]]

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May I know what you mean by this photo??

[[An...]]

Bending of granite and probe shaft.

[[Me...]]

I would tend to disagree about larger probes being more "accurate", specifically when it comes to form. The Cookbook actually recommends which size of probe to use per measuring diameter.

[[Cl...]]

What about the smoothing affect caused by larger diameter probes? Depending on surface finish, they tent to ride across peaks.

[[Ma...]]

While there may be some advantages to both of the cases mentioned, neither should be considered true as written.

[[Pa...]]

more accurate may have been the wrong word choice.
more repeatable due to:
1) less probe bending
2) smoothing of peaks and valleys
Do we have general agreement on this much?
PaulS

[[Ch...]]

As a general rule of thumb, bigger probes are more ridged, and you get some mechanical filtering of your data. Same as points 1 and 2 from above.

In the real world, this is not always the case. I have found situations that larger probes are less accurate/repeatable. Answer is to do good MSA on all critical measurements.

[[Ma...]]

I would agree that it is generally best to use the stiffest (shortest, largest diameter, hardest material, best construction) stylus possible without compromising other aspects of the measurement task (getting close enough to edges, too large relative to hole size, etc.).

[[Pa...]]

very good, thank you all