RUNOUT - what's the correct way

Depending up your probing system 200mm may be far too long. If it's a TP20 or Tesa MP type probe then this is the case.

You might get better results using more hits - these probes will give a tri-lobed (3 pointed) form, which gets bigger the longer the stylus. Using only 4 hits this will likely be skewed one way, assuming you're rotating the probe to get in each end this could have a significant impact.

You also need to make sure the probe calibrations relate correctly to each other (i.e. they are calibrated at the same time on the same sphere location ideally).

However, using this type probing for this (touch trigger probe with too long an extension) you are always going to be compromised in terms of accuracy and repeatability.


If it's an X1-S-H, X3, X5 or an SP25 with the appropriate module then you should be okay, but you should still use more than 4 hits.

For a 40mm diameter I'd probably use 13 to 17 hits.

The same as above goes for probe calibration however.


Probably more relevant is if neither A or B is big enough to measure as a cylinder (which would provide a stable datum to level to), then the drawing likely doesn't reflect how the part assembles and functions.

That said you should be able to generate a stable A-B datum from two circles to evaluate the dimeter at the far end of the tube.

You will never get good results check A to B if B isn't long enough (relative to the distance between A and B).

There's no real rules on number of points.

Ideally you'd increase the number of hits until it's not making any difference, but experience comes into this a lot depending on size, tolerances and manufacturing method.

There is a free NPL (UK's National Physics Laboratory) guide which talks about probing strategies - you should find it easily on google.

Even at 15mm and 16mm you should measure as cylinders really.

100mm long will actually give a more stable alignment than just going off the end face (so you level to the cylinder instead of the plane).

Alignments can have an impact of the GD&T depending on which dimensioning method you're using (Legacy vs Xact/Geometric Tolerances) and even then depending on how you use them.

There's no real rules on number of points.

Ideally you'd increase the number of hits until it's not making any difference, but experience comes into this a lot depending on size, tolerances and manufacturing method.

There is a free NPL (UK's National Physics Laboratory) guide which talks about probing strategies - you should find it easily on google.

Even at 15mm and 16mm you should measure as cylinders really.

100mm long will actually give a more stable alignment than just going off the end face (so you level to the cylinder instead of the plane).

Alignments can have an impact of the GD&T depending on which dimensioning method you're using (Legacy vs Xact/Geometric Tolerances) and even then depending on how you use them.