Thread Position and Datum Targets - How would you?

[[Ev...]]

Waiting on a sister company to run some prototypes through their CMM to do a small correlation study. I was on a call with Zeiss support and they weren't quite certain on how to report this, so back to the forums with me.

Datum A is comprised of 3 Datum Targets (A1 A2D2 A3D3), all non-coplanar. Datum D is comprised of 3 Datum Targets (D1 A2D2 A3D3), all non-coplanar. Zeiss tech recommended recalling them into a theoretical plane and using formulas to set them at the same Z height, so I set them to the bottom of H10 C'Bore as its marked as the origin on the print. This is a tab print, the size of the part im working with does not have H13-20, and the slot H23.

The threaded holes all have position callouts to either Datum A or D as the primary. Datum B and Datum C are points from the intersection of a plug gage and the respective counterbore plane, see below


I'm fine with creating all of this. What I don't understand is how to report to these. On a different part of the print, H11 & H12 have position callouts to D | B | C. Should I create an RPS alignment like so and report to this?

If so, how should I report features that only have a primary and secondary datum? Especially those that use the Datum Targets to make Datum A or D? Do I need to project the scanned cylinders from the plug gages down onto anything?

Side note, does it matter whether the RPS alignments are 3-2-1 or freeform? Basic training doesn't cover this, which is the only formal training I have, besides the infinite wisdoms of the forums 🙂 appreciate any help

[[Er...]]

To me it looks like you are on the right track.

I would use RPS for the base alignment ABC. A1(Z), A2(Z), A3(Z), B(XY), and C(Y)

For the AB callout I would use the ABC RPS alignment. Creating a plane out of A1 A2 A3 with Offset Plane could be a nightmare. I've done it, but I don't use it often so I have to relearn it every time 🤣

For the Angularity I would just create a D plane from the points and let the CAD figure out the nominal angle.

DB is a monster. That true position is really only asking how far away they are from each other. Maybe an Alignment with DBE?

[[Ev...]]

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Thanks Erik - this whole print/part is a mess. I used a 3D Best Fit for the base alignment, using the Datum Targets. Creating an alignment using B and C requires me to probe a plane in a c'bore which is just too dang small. I've had some good success with the 3D best fit.

The idea of an offset plane makes sense to me, but the applications engineer steered me away from it haha. I'll give some of these a shot.