Datum Targets and Circle for RPS Alignment

[[To...]]

I've got an air foil part. There are 5 datum targets A1, A2 and A3 for Spatial and Z, B1 and B2 for Planar and X. For the tertiary (Y), they're specifying a cylinder as Datum C. Do you think it would be okay to measure C as a circle, create a point, recall Circle_C and use in my RPS alignment along with my 5 other points?

I just noticed that I can select the circle in my RPS alignment, so I guess I don't need to create the 6th point.

[[An...]]

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[[To...]]

Here's a little more to this project.

I'm set on using the 5 datum targets for A and B to control Z and X in an RPS alignment. I was planning to use a circle on cylinder C as the 6th target point to control Y, but now I'm questioning if I shouldn't be using a cylinder instead of a circle. I know I can't use a cylinder for the RPS alignment but I was thinking I could use an intersection of the cylinder axis but to what? Can I use a theoretical X plane, located by the B points for my intersection? B1 and B2 both have the same X value relative to axis A.

Also, I'm looking at the True Position of C to A and B. Since A and B are not features that I can use in my TP, I'm planning to create a Geometry Best Fit Alignment using datum targets A1, A2, A3, B1 and B2 ( only allowing translation in the Y). Then, and do a best fit bore pattern of cylinder C to this GBFA. Or, should I just refer to the Base Alingment from above? Am I overthinking this?

For other features, that use A, B and C, my plan was to use the best fit bore pattern alignment. Sound ok?

I've attached a cleaned up drawing so you can sort of visualize my application.

How would you guys approach the alignment and the TP of C?

RPS Example 1.pdf

[[An...]]

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[[Br...]]

You could use the RPS alignment like you explained for your X and Z, then either use the circle of Datum feature C or just any point in the Y direction just to lock it down. Then create a regular alignment but have it reference the RPS alignment you've already made, and drop your Datum C cylinder in the Y origin box. Leave everything else blank and the alignment will refer back to the RPS alignment you made to constrain the other degrees of freedom.

[[To...]]

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I understand what you said but I have a question.

Let's say I create a standard alignment on a cubed part using 2 planes for Z and X origin and a cylinder for the Y origin, the Y zero would be calculated from the intersection of the C cylinder and X origin plane.

In my application, the location of the X origin is calculated from B1 and B2 but those points are not X zero on the model. Does this mean the Y origin will be calculated from the intersection of the axis of C at models' X origin.

[[Br...]]

That's a really good question. You could try to measure a circle inside the cylinder and see if there is a significant difference in location in the Y direction. You could also try to constrain the Cylinder in the Z direction in the alignment. Or you could create a theoretical YZ plane within the RPS alignment. this should be nominaly perpendicular to the cylinder if I understand correctly. With the form datum setting on, use an outer-tangential evaluation on the cylinder, and constrain it to that theoretical plane. Let me know if that doesn't make sense.