Datum as 2 cones

[[He...]]

I have a very large cylindrical part. Print requires position of cylinders along axis with the primary datum in DRF as 2 cones on opposite ends of the part labeled B-C. My secondary datum is a plane perpendicular to the axis. I currently have a 3d line recalling the cones and using that as the primary datum. Is that correct? Print is to ASME.

[[Ri...]]

They want it held between those two centers. You're going to have to have a discussion with your customer on a compromise on measuring this part. 

[[Ky...]]

I don't see datum B on the print sample you showed but if they are on opposite sides of the part, you are on the right path.

 

I wouldn't even bother measuring C as a full cylinder. It's too short to really be measured as such. I would probably measure it as a circle on cylinder (should just be able to click with the circle making tool if you have a CAD) and then make a 3D line using recall between the two circles (note, it must be recall and not recall feature points). That's how I would make B-C

[[Ri...]]

Use circle on a cone for both centers.

[[Ma...]]

I would use Circle on a Cone on both ends and create a 3D Line between those circles.

[[DW...]]

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 Richard is on the money here. Of all the things I have measured with the CMM, the runout/position of cylinder axes on shafts is the most difficult, especially if the manufacturer is grinding/lapping. It's all in the setup, which requires some very specific equipment. To get the most accurate and best correlating results with the shop floor, you are going to need a surface plate, bench center with appropriate sized anvils, and a high resolution dial or digital indicator. The CMM just falls short in these types of measurements (in my opinion). Best of luck sir.