Perpendicularity

[MFCguy]

I am having some troubles with a perpendicularity measurement. I am measuring two circles and construction a cylinder to get the centerline/ axis. I then am trying to get the perpendicular measurement to a plane. I am wondering why the measured values come out so drastically different depending on which feature I select first.

I am getting around 12 microns it is plane to cylinder
And about 70 microns when its cylinder to plane

I do not comprehend how they wouldn’t be the same value, and any and all help would be greatly appreciated.

THANKS

[craiger_ny]

The order you pick determines the datum. If the cylinder is shorter than the plane is wide then the cylinder is not cocked off as much relative to the plane as the plane is relative to the cylinder. This one is hard to put into words hopefully someone will be more articulate with it or present a sketch.

[cmmguy]

You did a good job....

Hows this: Ratio of Error

[Jan d.]

Not sure, but what version are you running? I was told (but have never had the pleasure to experience ) that any version before V4.0 did not construct cylinders from circles correctly. Supposedly fixed starting in V4.0.

Jan.

I am having some troubles with a perpendicularity measurement. I am measuring two circles and construction a cylinder to get the centerline/ axis. I then am trying to get the perpendicular measurement to a plane. I am wondering why the measured values come out so drastically different depending on which feature I select first.

I am getting around 12 microns it is plane to cylinder
And about 70 microns when its cylinder to plane

I do not comprehend how they wouldn’t be the same value, and any and all help would be greatly appreciated.

THANKS

[MFCguy]

I am running 3.5 on this CMM. I am working on pictures to better describe our desired measurement.

[craiger_ny]

Not sure, but what version are you running? I was told (but have never had the pleasure to experience ) that any version before V4.0 did not construct cylinders from circles correctly. Supposedly fixed starting in V4.0.

Jan.

Boy I hope that gets confirmed man. If you find out for sure post it. Ever since we've had the ability to do it with circles I jumped right on it. I thought that was a huge improvement over the old construct a line trick or measuring points to construct. I think I'll start using the CIR1.HIT[1..8] trick from now on.

Thanks

[#2#]

The order you pick determines the datum. If the cylinder is shorter than the plane is wide then the cylinder is not cocked off as much relative to the plane as the plane is relative to the cylinder. This one is hard to put into words hopefully someone will be more articulate with it or present a sketch.

I'll work up a quick sketch that shows what I understood Craig to say.

[#2#]

The order you pick determines the datum. If the cylinder is shorter than the plane is wide then the cylinder is not cocked off as much relative to the plane as the plane is relative to the cylinder. This one is hard to put into words hopefully someone will be more articulate with it or present a sketch.

I'll work up a quick sketch that shows what I understood Craig to say.

Here you go. The blue lines represent the perp. value reported. Clearer now?

[MFCguy]

The cylinder is constructed from 2 circles at different heights, and then there is a 3 hit plane taken inside of the red circle. I want to know if the plane is perp. to the centerline of the cylinder.
It is called out as a flatness zone on the print, but the plan could be scewed on any angle and still be flat.