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incorrect profile tolerance band

JFournier
Hey everyone,

I'm trying to figure out why my profile tolerance band is in the Z-axis, instead of the X/Y-Axis. As you can see below, the green arrows are a different set of points but represent the tolerance band I'm looking for. The red arrows show the points not being evaluated correctly. My points all seem to have the correct vectors with values in I and J, but alas, I'm still getting Z axis deviation. I've created a set of these vector points, and I'm evaluating using surface profile in GeoTol to datums ABC. Everything was measured and evaluated in the Z-Plus workplane.



​It should be noted my points are all .003" above Z zero on purpose, because that edge is too shallow for a 0.3mm probe to fit entirely. Our engineers have created offsets to compensate for all that, etc, and whether that's an acceptable route or if this is the right tool for the job won't be the focus here lol. But, if someone thinks the Z-height of my points is contributing, this might be good info to know.

Thanks in advance!
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  • Just throwing out some thoughts.

    If you are using an analog probe, it may be detecting the deflection vector of the probe as the measured vector. It would deflect up quite a bit since the center of the probe is above the face of the part and the probe radius is so small. You might be able to avoid this by changing the Snap properties to Yes. That would force the probe to report the point at the nominal height and vector.

    Hexagon was sending out email newsletters a while back that included a tips and tricks article. I only ever remember receiving one such email. I remember that the trick discussed in that email was a way to probe an edge feature like that - smaller than the probe radius. It involved disabling probe radius compensation to measure the points. That way the point location is then measured at the center of the probe tip, rather than automatically compensating for the probe radius. Then you use a bit of trig to calculate the actual position of the edge using the height of the probe above the edge and the nominal probe radius. I wish I had a way to see that article again. I have never tried it and have my concerns about how accurate it is (it assumes no tunneling error), but thought it was a nifty idea.



Reply
  • Just throwing out some thoughts.

    If you are using an analog probe, it may be detecting the deflection vector of the probe as the measured vector. It would deflect up quite a bit since the center of the probe is above the face of the part and the probe radius is so small. You might be able to avoid this by changing the Snap properties to Yes. That would force the probe to report the point at the nominal height and vector.

    Hexagon was sending out email newsletters a while back that included a tips and tricks article. I only ever remember receiving one such email. I remember that the trick discussed in that email was a way to probe an edge feature like that - smaller than the probe radius. It involved disabling probe radius compensation to measure the points. That way the point location is then measured at the center of the probe tip, rather than automatically compensating for the probe radius. Then you use a bit of trig to calculate the actual position of the edge using the height of the probe above the edge and the nominal probe radius. I wish I had a way to see that article again. I have never tried it and have my concerns about how accurate it is (it assumes no tunneling error), but thought it was a nifty idea.



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