True Position Question

[[Am...]]

Im questioning the true position result im getting on one of my programs. Im getting the true position at 0.103", however when I look at the position of the cylinder in the features my Z position is .001" from nominal and Z is .003" from nominal. Im not sure if im missing something here but it seems like I should be closer then .103".

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[[Me...]]

Your constraining the features differently in your True Position evaluation than your Base Alignment. You have your spatial set to -B- in the Base Alignment and set to -A- in your True Position. Your feature numbers are representing the location relative to the Base Alignment.

[[Am...]]

I've tried it with B as primary and A as secondary but the result was about the same .102" The reason I have them as AB in the true position is because those are my primary and secondary datums.

[[Am...]]

Went and tried it with a new base alignment with A spatial and B as planar, it made no difference to my results. Should I just do this as a circle and check in two places?

[[An...]]

See attached.

Contribution_07_03_2019.pdf

[[Me...]]

Based on the image you posted is it safe to say that the Cylinder you're measuring is a cylinder at an 8° angle?

If so, you may want to create an Alternate Alignment and rotate it to 8°, or in your True Position Characteristic, click the "Special" button and rotate to your 8° in there.

[[Br...]]

Yeah, good catch Shawn. you need to click that "Special" button in the True Position window and rotate the alignment so that it is nominally parallel with the feature you are evaluating. Most of the time I try to mach it up with the basics on the drawing. So if there's some intersection point, and an angle going back to the datum features, try to get the coordinate system there. it will make more sense to you and you can verify the nominals you're getting off the CAD are correct.

[[Am...]]

Yes the cylinder is at an 8° angle, I did rotate my true position and that made a big difference bringing it down to .010". I didn't think I had to use that in this type of case but it makes sense. Thank you guys. Another quick question I have is where does Calypso determine the staring point of the cylinder? At what point of the axis does it choose?

[[Al...]]

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The starting point is shown in the nominal data portion of the feature; the axis travels in the direction of a2 (-8 deg) for the depth shown.

[[Ja...]]

"At what point of the axis does it choose?" I am curious as well. It should evaluate the entire axis.

[[Me...]]

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The evaluation range is the "depth" setting in the cylinder feature
The TP will be reported by the highest result along the hole range

[[ro...]]

if you go to RESOURCES>PRINTOUT>AXIS END POINTS FOR POSITION TOLERANCES. what you will get for a result on your report is the true position at the top of the axis and another one for the bottom of it.

[[Su...]]

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In the above case cylinder axis angle is 8°.after some cases it will vary (just assume) like 2° something,at that time/every time I need to go to special option and change the angle. Is there any option for AUTOMATIC change of angle in base alignment special button also.(what the angle achieved in cylinder that is automatically came to special button/option).

[[Br...]]

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You should only have to change the angle once. What you're doing is setting the nominal/basic location of the feature. e.g. You're telling calypso where the tolerance zone is. If its supposed to be at an 8° angle, but its manufactured at 6° or 10°, causing it to violate the boundary of the tolerance zone, then it is simply out of tolerance. Adjusting the angle to make the numbers good is akin to changing the X or Y values to make the the position come in tolerance.