Probing problems?

[powerfulp]

I am having problems holding positioning of bores to the c/l of a 25" OD, which I probe to find the c/l of.

 

The machine is a Horizontal Machining Center (Mazak) 800mm size. I am probing a 25" OD using program O9823 which probes in (3) place and gets the c/l. I do this three separate times in different locations and take the average c/l of each to determine the final c/l position.

 

We then machine some bores that are dimensioned to the c/l of that 25" OD.

 

We can run one part and it is ok, then the next it is not. I don't understand how it could be out when we are probing for c/l like we are.

 

Does anyone have any ideas as to why the bores would be out of location to the OD we probe?

 

NOTE:

The parts are clean.

The probing is done right before the finish boring so the machine temperature is the same when probing and boring.

 

Any input is appreciated...

[disciple]

What tolerance are you trying to hold? How far out are they? Are they off location in one axis? Are you drilling the holes on the outer reaches of the pallet, causing it to twist under pressure? Please provide some details so we have an idea of what's happening..

[powerfulp]

Ok

 

There are two decks of bores. Four bores on the upper deck and four on the lower deck. They are supposed to be inline within 0.001" and have a diametrical true position tolerance of 0.002" back to the OD that is being probed.

 

What QA does is find the c/l of the four bores and with that info they project the c/l of the four bores in the X & Y-axis. Can be vary from part-to-part over 0.002" linearly (average c/l position of all 4 bores).

 

I don't understand how this can be. And it's happening on more than one machine. We have been running these parts for years and have always had a problem when we switch from one style to another.

 

If the probe is running true, calibrated and clean (and the part is clean) - how can this be?

 

Thanks.

[taperlength]

Possible sources of error: QA not inspecting correctly, OD of part is out of round, faces of part are not parallel, Z axis on machine is not trammed, backlash in X and/or Y axes.

[Dave Ball]

Which probe model? Not all probes will run the 9823 (3 point bore/boss) cycle correctly, You must have a strain gage probe and you must have ran the 9804 (REN CAL VEC STYLUS RAD) calibration program.