Measurement Strategies for a diamond pin

[WaveLine]

What's the cliché? Long time listener, first time caller.

So I have a bonding fixture with some really tight tolerances, and one of the datums (specifically Datum C) on the tool is a diamond pin. It's a 0.1878 diameter pin (+0.0002 / -0.0000) with a 0.001 true position to |A|B|.

This is the first time I've been asked to measure a diamond pin, so I'm curious if anyone has had any success measuring these kind of features and how they go about measuring them.

I've tried measuring a circle around the rounded portions of the pin only. I've tried measuring a cylinder around the same rounded portions. I've measured angle points on the intersections of the flats, created a line between the two and constructed a cast point on the line. I haven't yet tried measuring four planes on the flats, but I might give that a shot too.

They all seem to "work", but I wonder which might be the preferable way?

So how do you measure diamond pins? Any problems to watch out for?

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[Matthew D. Hoedeman]

Is it for a ROUND hole, and thus the 2 radii are actually 2 segments of the same circle? If so, then the flats are 100% useless for anything, as they are just clearance.

I would manually LEARN a hole (not pick from cad) and take a minimum of 5 hits on each radii (10 hits total) for a learned circle. I would then adjust the "Z" value of all the hits to the same level, then measure it. You could try to do it using CAD and moving all the hits around, but that takes WAY longer than just learning a circle.

Generally, the diamond pins I see are for locating a slot on the flats, and the rest is clearance (opposite of what I ASSume you have)

[Schrocknroll]

Is it for a ROUND hole, and thus the 2 radii are actually 2 segments of the same circle? If so, then the flats are 100% useless for anything, as they are just clearance.

I would manually LEARN a hole (not pick from cad) and take a minimum of 5 hits on each radii (10 hits total) for a learned circle. I would then adjust the "Z" value of all the hits to the same level, then measure it. You could try to do it using CAD and moving all the hits around, but that takes WAY longer than just learning a circle.

Generally, the diamond pins I see are for locating a slot on the flats, and the rest is clearance (opposite of what I ASSume you have)

This is what I have done in the past. A diamond pin is only used for rotational alignment in line with the radii, the flats are just clearance as Matt said. The location of the circle created may not be perfect in the direction of the flats, but that's OK since it's not used in that direction. Once you have created the circle it should only be used for rotating the alignment, not setting an origin.

[Roberto]

Is it for a ROUND hole, and thus the 2 radii are actually 2 segments of the same circle? If so, then the flats are 100% useless for anything, as they are just clearance.

I would manually LEARN a hole (not pick from cad) and take a minimum of 5 hits on each radii (10 hits total) for a learned circle. I would then adjust the "Z" value of all the hits to the same level, then measure it. You could try to do it using CAD and moving all the hits around, but that takes WAY longer than just learning a circle.

Generally, the diamond pins I see are for locating a slot on the flats, and the rest is clearance (opposite of what I ASSume you have)

Similar technique here, except that I use program mode (ctrl+F4) to pick the circle from the Cad.
I take 3 hits for a learned circle on one of the pin radii and press done (don't measure it). Press F9 to adjust the Z value and increase hit#, set angle 0 to 360.
Press OK and say yes to the equally spaced hit?
Finally, highlight and delete the code for the hits on the flats leaving only the ones on each radii. Execute!
(Make sure "MOVE/CIRCULAR" in between hits as well as prehit/retract is properly set).

[Lord_Warfield]

I would just take one point on each side of the radii (with perfect vectors and XYZ values) and create a center point. You only really need to know where the center is...

[Lord_Warfield]

If the diameter was also needed I would just mic it and use a key in

[BKulpa]

I'd use an auto feature circle with 7 points, 3 on one radius 4 on the other.