Alignment Question. BF Line between Holes vs Autoalign Cylinders

Hello. I am programming a part using legacy. The top plane is the primary datum and the seconary/tertiary datums are two thru holes that are square to the top plane. So rotate to the line between the holes of course.

I have profile of a surface called out to these datums.

I tried two alignments:

- One alignment uses cylinders. I autoaligned to the top plane and the 2 cylinders.

- The other alignment I created a 2d best fit line between the cylinders. I autoaligned to the top plane, the best fit line, and one cylinder as my tertiary datum.

My profile of a surface looks crooked when I use the first alignment, and it looks much better using the second alignment. Can someone explain why my results would be different? Should I go with alignment #2? Please see screenshots.

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MattR over 1 year ago

Go with what Matt said. All of these gimmicks to make programming apparently "faster" are just sales pitch to QA managers who have no idea how CMM really works.
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Lukas over 1 year ago in reply to MattR

Thank you, Matt. I will stay away from Autoalign from now on, especially when it comes to Cylinders. I wonder if it would have worked ok if the holes were circles.
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Lukas over 1 year ago in reply to MattR

Thank you, Matt. I will stay away from Autoalign from now on, especially when it comes to Cylinders. I wonder if it would have worked ok if the holes were circles.
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