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NC Pros and Cons

acgarcia
Looking to get into PC-Dmis NC. We currently use Renishaw touch probes to locate parts. Never used them for actual measurements.

Some info:

I'm a CMM guy, not a machinist, is that a problem for NC?
The machinists we do have tend to crash the machines a lot.
Trying to reduce or eliminate human qc steps.
Make small and large parts for oil and gas industry.
Tightest tolerance would be 0.0005in.
Mostly steel, some brass and aluminium.
Machines are Haas mills and Mori multi turning centers. Mori Lathes, 1 Toshiba large boring mill.
Don't know if I need 3, 4 or 5 axis NC Options.
What if I what a singe probe and a star probe?

I got some info from our sales person but I'm still looking for other info. Seems to be cheaper than buying another CMM. We are buying new CNC mulit turning centers like ever other month now. Most of which have tooling carousels with plenty of free space. One purchase came with a renishaw probe that uses radio frequencies. A mori person was here setting it up to locate the part. I asked her about actual measurements and reporting but she didn't know about that side of it.

Any advice or input would be appreciated.
  • in reply to acgarcia
    Hexagon sells their version of machine probes in case you didn't want to use or have a Renishaw probe.
  • in reply to acgarcia
    Oh, M&H probe line that hexagon bought. I forgot about that. Thanks!
  • Vinni is spot-on with discussing calibration here, and ACG, you do need to pay attention to it. Hexagon (and disclaimer here: I'm a hexagon guy) doesn't talk enough about calibration/certification of machine tools, but to be fair to the team, they are mostly involved on CMMs, and the whole concept of certifying Machine Tools for measurement is still not well defined terrirory.
    There is an ISO workgroup that Hexagon is even involved in to come up with a standard way for certifying machines for inspection and to which accuracy.

    That said, we can really only talk about best practice. And that is to have a machine well maintained. That means getting its squareness right, checking the rotary axes and the keeping an eye on the machine to make sure it does not wander off of some reference values.

    The best way is of course to compare a part measured on the machine to the same part measured with the same points on the CMM. PC-DMIS NC is a big help in accomplishing that because the programs can be moved with some massaging from CNC to CMM or vice versa or at least similar programs can be created on both.

    Also an important point is that the math will be the same. If you were to measure on a CNC with any of the "classic" probing cycles that the probe vendors deliver, the macros onyl use a simple math, that is not certified like that in CMMs, so comparability to CMMs dissappears.

    Other methods are to use a ball bar or other tools (look out - Hexagon pitch: Check out what ETALON has to offer here) to monitor the machine performance

    But at the end of the day, since there is no standard accepted, and also CNC machines are typically used in rougher envrironments than CMMs, it really comes down to finding ways to estabilsh trust inwhat the machines are doing and how they behave.
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