NC Costs?

OMG is not only for large parts.

Hey Jan, are C axis part of the calibration? I am thinking of backlash issues that I have seen on machines that are not supposed to exhibit backlash. Or is the C axis not part of the measurement routine? I know nothing of PCDMIS NC. I am in J's camp where I will not lend any credibility to a machine tool's measurements for the most part. But I can see a value for in process monitoring especially on large parts, long run times, situations where breaking the setup is timely/costly, I'm sure the reasons add up. I know you are doing well by it but do you have any pitfalls to share. Things that you have to work around perhaps?

Craig

We are measuring extremely close tolerance parts on very very good machines. I have correlation with a Zeiss UPMC Karat to within 0.0002". I used to be in the camp of the doubters, until I actually started to do the work.

The key is to have very very good machines. That means dimensionally stable and with limited backlash. And you need to calibrate them, just like you do your CMM and yes, this includes the C axis. By the way, typically, you can only correct for angular errors. After you know how your machine performs as a CMM, then have artifacts that make sure that the machine remains accurate: in other words, start to treat your machine like your CMM. Our most accurate machines are sitting in our CMM room, side to side with the Zeiss's.

We have rotary tables that have encoders mounted directly to the rotary axis shaft. We do NOT monitor the motor encoder position. Therefore backlash is a minimal issue for us. Our biggest challenge on the rotary is actually the wobble. We spend an awful lot of money to keep that to a minimum too.

I use PC-DMIS with the rotary option on my most challenging part. I found that most features can be measured without re-datuming, except at one angle. We found that that specific angular position is the area where the wobble is the highest (with respect to the starting position). For that position I had to re-datum in order to be able to measure surface profiles to a 0.0004" FCF.

I am finding that my best machines can measure with very close correlation to my best CMM's. It is a mistake to think that OMG is only for large parts.

The savings are reduced load on the CMM's (I will never state that CMM's will be eliminated, because that is simply not true), improved process flow and improved quality ownership by the operator (because he has immediate on-the-machine, in-the-fixture results).



Jan.

OMG is not only for large parts.

Hey Jan, are C axis part of the calibration? I am thinking of backlash issues that I have seen on machines that are not supposed to exhibit backlash. Or is the C axis not part of the measurement routine? I know nothing of PCDMIS NC. I am in J's camp where I will not lend any credibility to a machine tool's measurements for the most part. But I can see a value for in process monitoring especially on large parts, long run times, situations where breaking the setup is timely/costly, I'm sure the reasons add up. I know you are doing well by it but do you have any pitfalls to share. Things that you have to work around perhaps?

Craig

We are measuring extremely close tolerance parts on very very good machines. I have correlation with a Zeiss UPMC Karat to within 0.0002". I used to be in the camp of the doubters, until I actually started to do the work.

The key is to have very very good machines. That means dimensionally stable and with limited backlash. And you need to calibrate them, just like you do your CMM and yes, this includes the C axis. By the way, typically, you can only correct for angular errors. After you know how your machine performs as a CMM, then have artifacts that make sure that the machine remains accurate: in other words, start to treat your machine like your CMM. Our most accurate machines are sitting in our CMM room, side to side with the Zeiss's.

We have rotary tables that have encoders mounted directly to the rotary axis shaft. We do NOT monitor the motor encoder position. Therefore backlash is a minimal issue for us. Our biggest challenge on the rotary is actually the wobble. We spend an awful lot of money to keep that to a minimum too.

I use PC-DMIS with the rotary option on my most challenging part. I found that most features can be measured without re-datuming, except at one angle. We found that that specific angular position is the area where the wobble is the highest (with respect to the starting position). For that position I had to re-datum in order to be able to measure surface profiles to a 0.0004" FCF.

I am finding that my best machines can measure with very close correlation to my best CMM's. It is a mistake to think that OMG is only for large parts.

The savings are reduced load on the CMM's (I will never state that CMM's will be eliminated, because that is simply not true), improved process flow and improved quality ownership by the operator (because he has immediate on-the-machine, in-the-fixture results).



Jan.