Perpendicularity, oh the horror

[cappel]

Oh good sirs:

I measured a cylinder. I leveled to that cylinder. I measured a plane. I dimensioned the plane's perpendicularity to that cylinder. It measured about .02”. However, no single point on that plane measure more than .002” from any other point. Why would there be such a large discrepancy????

Thanks

Fred

[ag162]

Hello,
The problem most likely lies within the alignment. Measure several points on the plane and it should show how the alignment may be skewed.

Hope this helps,
A.Gore

[cappel]

I did that. None of the points deviate by more than a thousandth or two.

[cappel]

Chew on this for a minute.

I constructed a plane perpendicular to the afore mentioned cylinder.
The two planes are parallel within .0015.

How could this be?

Thanks in advance

Fred

[Schrocknroll]

I have 2 thoughts. On this that is.

1) Make sure your projection distance is zero.

2) How straight and round is your cylinder? I know if you call out parallelism of 2 planes, the flatness of both planes will affect the results. It might be similar with perpendicularity.

Just some my 2 cents.

[cappel]

Hmmm

That didn't work, but thanks for you two cents

Fred

[jacyEd]

I have a similar issue but much more severe. It seems there is little support for those who do not use CAD models. I cannot get proper hight measurements, concintricity, even diameters are going heywire. 12" out of round is not an uncommon error im getting on a part thats round within .001"

[John Kingston]

Are you using autofeatures or "learned points" (taking hits manually)? I also rarely have a cad model, but have learned much from the folks here and at PC-DMIS.com . The direction, number and order your points are taken. For a cylinder I take a minimum of 9 points. Four on the top level, four on the bottom and 1 in the middle. If you can, post the part of your program giving you problems. All of us will try to help!

[cappel]

Please find attached the portion of my program that I am having trouble with.

[johnboy]

I don't see that you ever leveled to the cylinder. Level to whatever is the Datum.
When checking perpendicularity be sure to select the feature first, then the Datum. Look to make sure you are not extending the reference length of the cylinder or plane.
BTW, for constructing the cylinder I select the points in a 'spiral order' from one end to the other.