True Position Repeatability

[mds_toronto]

There's a bore that I measured (offline to online) and I can only hit it 50% of the circumference due to the complexity of the part. When I get the true position of it we found it within the 0.005" call-out (actual 0.003")and we almost accepted the part as good. We used the other cmm and gave us more than the limit (0.007").

Now we did a repeatability on both machines using 4 different angles and giving us a min/max range of up to 3 thou.

Do you think what causing the non-repeatability problem is because I'm only hitting 50% circumference of the hole or is it a hardware problem (e.g. probehead, tp20, etc.).

Thanks in advance guys,

mds

p.s.

the cmm that's giving us out-of-spec TP is the older machine. the good result is coming from the newer cmm though the repeatability is not good.

[craiger_ny]

Do you think what causing the non-repeatability problem is because I'm only hitting 50% circumference of the hole

Yes

[Underspec]

re-calibrate the probe tips, make sure both have same move, hit, speeds.

[Jan d.]

How many points do you take? How well are the spaced out? Do you use the cylinder or circle features to evaluate?

[mds_toronto]

i used a circle feature using 6 hits...no initial hits...i just found out that we're using 2 different tp20 module. one cmm is medium force and the other extended...

[Matthew D. Hoedeman]

Well, as long as the calibrations of the tips came out correct, that really should NOT make a difference in the results.