measurement setup -height characteristic

[[Ja...]]

Hi everyone,

I have this part (see attached pic). I am trying to measure height dimension as shown. FYI, the plane to which height is to be measured is long as shown but smaller in width. There is a hole on datum -A- plane to clock the part (not shown in pic)

How would you establish base alignment, height characteristics? (strategy, filter, constraints,etc)
I used probing instead of scanning as this is aluminum material.

I have tried with:
Base alignment: Datum-C- on fixture as primary datum with outer tangential evaluation(spatial rotation and 2 origins). Datum -A- with LSQ evaluation as secondary datum (1 origin). and hole on datum -A- as tertiary datum ( planar rotation).

Fixture is put on a magnetic block, Dat-C- cylinder is measured on fixture, part is loaded on the fixture and tightened with cover and rest of measurements are carried out on part.

Height measured with cartesian distance from plane to cylinder dat-C- (plane constrained to cylinder dat-C-).
I used surface profile feature with geometry best fit with best fit allowing rotation around dat -C- cylinder as sanity check. I trusted profile results rather than cartesian just because cartesian distance will give me distance at the feature origin which is not on the part itself.

The problem is customer had this dimension always shown higher than what I got. I could not figure out why.

Screenshot 2021-08-16 101910.png

[[Cl...]]

When in doubt I like to go to the old fashion manual surface plate layout if possible.

[[Da...]]

Maybe, instead of using cartesian distance, they just report the Z from the plane feature?

[[Ja...]]

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So that's another thing, I laid the part down on suface place with the plane touching surface plate and pin in datum -B- hole and measure/calculate the height dimension at both ends of datum -B- using indicator dial height gage. It showed me that the dimension is within/ under the limit.

Now customer has a long pin mounted on V-block and is using height gage/ indicator setup where they center on the pin using height gage centering function, then mount the part, manually level the plane with indicator and then probe with height gage on top of that plane. and it showed them over the limit.

[[Ja...]]

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Yes that's what they do and they have a different cmm than zeiss but as in my earlier reply they also use height gage verification.


Right now I just want to know how will you guys setup up your program for this part.

[[To...]]

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Cartesian Distance will give the distance from the mid-point of Feature 1 perpendicular to Feature 2. Similar to a Perpendicular Construction without creating the 3d line. However, if you want a visualization, use Perp Const.