Center line to hole measuring method?

[[Lo...]]

Hello everyone, 

I could use some direction on an issue I am having. The part pictured, I was trying to measure the center line of the part to the center of the holes that have red dot's near them. I created center lines through the 3 holes pictured on the X axis and then a center line from each center line in the holes along the X axis. Used cartesian distance from the hole to the center line. The result was both holes were shifted on the Y+ axis by .100-.150. I also used a center line in the holes and did a cartesian distance to the center line on the X axis and still dimensions were shifted .100-.150 on Y+. Just for reference, measured the holes from inside edge to inside edge with a caliper  just for reference and they measure the same, not the .100-.150 I was seeing. I am not sure what I did wrong, I don't see these holes being off that much. What method should I use to measure this distance?

Thanks,

Lou

Edited 3 hours ago

[[Ke...]]

3 hole X axis centerline - What is the straightness? (is one of the holes shifting the centerline)

How does your certesian distance compare with creating a perpendicular from the red-dot-holes to your X axis centerline?

[[Lo...]]

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Thanks Keith,

3 hole X axis centerline straightness result is 0.000. 

Created a perpendicular from the red dot holes to the X axis centerline and it is showing a shift in the Y+ but it's .007 not .100-.150 like I was getting before. I did the same with the remaining 4 holes and am getting .006-.007 out of tolerance dimension. 

Clearly the creating the perpendicular line worked, and will be using this method going forward. But, I don't understand why the cartesian distance from 3Dline to 3Dline would be so far off? 

Side note, parts have been taken off CMM and sent off to the next process. Management deemed them good.  

 

[[Ma...]]

How you filled cartesian distance? First element should be that hole and as second should go that 3d line.
This way it should create perpendicular distance from 3d line to the center of hole.

If hole is measured as cylinder, then it can give different results while filled first 3d line and then the hole.

[[Ke...]]

As Martin alluded to, the cartesian distance measures the straight-line distance between two features, with the first acting as the origin, and the second defining the orientation/direction. So, results may be dependant on how they are entered. Typically, you would want to use the largest feature in the second selection... I find it to be counterintuitive and tend to use Perpendicular Distance, Symmetry Plane, or Caliper Distance for most evaluations.