Cylinder as planar rotation?

[[Th...]]

Apologies if this seems like a very basic question. It probably is.

I've recently come across a part I need to program, and near the end of it I realized I haven't had to deal with this before, and thus don't really know the proper solution. My C datum on this part is the center axis of a cylinder that fits through two other cylinders, separated by a gap. This cylinder's axis is parallel to the axis of my B datum. I seem to recall that Calypso won't correctly establish an alignment if the feature used for the planar rotation is parallel to the axis of origin. What's the correct way to do this?

I drew a picture to try and illustrate what I'm dealing with. Hopefully it's not too bad.

lookhowgoodiamatdrawingyouguys.jpg

[[Ja...]]

Couldn't you measure a circle in the top hole of -C-, another in the top hole of -B-, create a line through their centers, and use that as your rotation?

[[Th...]]

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That gives me weird results with my secondary alignment. If I recall the circles into a 3D line and establish it as the planar rotation feature in +X, the coordinate axes it generates make it look like it's in the -Y direction. Same thing happens if I use a recalled cylinder. I can't remember the specifics, but I read somewhere several months ago that Calypso can't rotate a line around a parallel axis like this.

[[Ja...]]

I just made a basic model in SolidWorks and I had no issue performing Spatial Rotation to -A-, Planar Rotation to 3D Line formed from a circle in -B- and a circle in -C-, and origin X, Y on -C-, Z on -A-.

No funny rotations on my end. Are you trying something different?

[[Th...]]

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Oh, I was attempting to rotate a line through both C circles around the B axis. Constructing a line from B to C works just fine, although C to B does not. I'm assuming the line origin is important too. I totally misread your post and for some reason thought you'd asked for a recalled line from the top and bottom C circles instead of what you actually wrote.

[[Ja...]]

I'm having no issues with what I choose as the first feature in the creation of the 3D Line. The only difference is the vector will be in the opposite direction, and the Planar Rotation needs to change from +X to -X for example.

Does that help you out with your program?

[[Th...]]

Yeah, it helped. I didn't know about the reversed vector thing, so I just figured the line from C to B was giving me a bad alignment. It's rotated correctly now.

As far as evaluating features to this DRF goes, is there anything else I need to do to the C datum? The line is just using the center point of one of the circles, but I would need to use a cylinder perpendicular to the A datum that fits through both sides of my C feature, correct?

[[Me...]]

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Yes, and this can be accomplished by recalling all |C| points into a circle that has been “constrained” to the primary datum. The same can be done for |B|. Assuming the fitting algorithms are the same, the calculated coordinate system will be the same as using constrained cylinders as the secondary and tertiary reference within a position characteristic.

[[Th...]]

OK, I think that makes sense. I define the top and bottom C circles, recall feature points from both into a third circle at the same location, and when I establish my DRF for position characteristics, I set that circle as tertiary and constrain it to A.

As for datum B, I got a little hasty sketching out that drawing and it's actually only on one side of the gap, but if it were gapped like C is, I would follow the same setup.

[[Me...]]

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Since |B| is defining the origin, and establishing the remaining two mutually perpendicular datums planes, you can use a cylinder regardless if it is on one side of the gap. It would also need to be constrained to the primary datum. However, recalling points into a circle just as |C| would yield equivalent results.

You may already know this....

Constraints can be applied within a secondary alignment by selecting the "ISO 5459" button located in any of the feature’s constraint tab. This happens automatically within position / profile characteristics (assuming your system is setup to do so), but it must be done manually within secondary alignments.

[[Th...]]

It all worked as it should. I did use the automatic ISO 5459 setup button to constrain the features in my secondary, and I evaluated my positions and profiles to it.