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Looking for new portable CMM

Nguyen
Hi all,
I'm looking for a portable CMM and found some Romers but not sure which one is best fit my need. I need a touch probe CMM, (PC-DMIS software preferred) to measure the mold/die feature mounted on the machine. Accuracy about 0.0002", arm is able to reach 40". I already submit a request to Romer but still want to ask your opinion on any pros and cons of the portable CMM? What machine type you have or suggest, etc...
Currently we have to disassemble the mold/die to put on the CMM to meaaure so I'd liek to avoid that.
Thank you in advance.
Nguyen
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  • That may be, but I am not intersted in B89.4.22 results when in real world applications +/-.010 is what you get.

    We had a salesperson bring an arm out for a demo. I presented a part that simplified was a block with a tab sticking out one side. There was a hole in the tab. The Datums were the pretty obvious 3 mutually perp planes. I wanted to know how well the arm could report the location of the hole and the thickness of the tab. Both had been measured several times by myself and 3 others using CMM, microhite, a micrometers (for the thickness.). I asked for thickness first, they could not get closer than .008 to the actual thickness and their repeatability was equally horrid. I did not even bother asking for position after that.

    That is the extent of my personal arm experience, but I have conversed with many who use arms and CMMs for a variety of applications.

    Arms are great for some things. They can do what they can do. Tight tolerances they can not do.

    Oh, and I have not even gotten to the numerous reports of frequent encoder failure & costly replacement (In terms of both $ and downtime).

    Lastly in the interest of full disclosure, do you work for an arm company or a division of a company that makes sells arms or arm software?


    lol, I love this guy.

    Wes as someone who worked with DCC CMM's for about 8 years before messing around with PCMM's, here's my take on it. You are entirely operator dependant using a PCMM. Smaller probe shafts flex, and larger ones can't get into certain areas. The "cone" style calibration that is generally provided for tip calibration leaves much to be desired. In the world of PCMM's it is all about technique.

    Granted you can't hit .0002" accuracy with an Infinite 2.0, but I do believe you can hit the +/-.0006" stated above, but precautions need to be taken. If you need tighter accuracy, you have to stick with the larger probes (8mm to 15mm range) and they can't stick out too far. Calibration needs to be done to a Calibration Sphere, not a single point cone check (this is 20 hits with the probe sitting inside a cone, rotating the wrist around in different directions. here the stylus nominal diameter is used for calculations, and if the styli isn't exactly the number used you have problems). After this, holes need good sample hits, single points need good sample hits, the operator needs to be careful. Technique and Setup are also important at this point. Whether it's on a tripod or using the magnetic base, it needs to properly secured, and the relationship to the item being measured needs to held. At one facility, we have a granite surface plate with a 1/2" plate of steel bolted down to it on one end. The Arm is attached via the magnetic base to that plate, and anything being measured is clamped to the granite surface so that the relationship between arm and part never changes. That same facility uses a 30mm Calibration Sphere. At that facility, probe calibrations are within .015mm(.0006") all the time (edit: this includes a 3mmx20mm probe, which is the one that gets close to the .015mm), and that arm is a 3000 series (old). Another facility uses a 5000 series arm (newer but not a 2.0). They have a steel table instead of the granite surface plate, and use the cone method for calibrations. Their probe calibrations range between .040 and .065mm. The steel table is about 7'x7', braced with tubing around the outside and a cross throught the middle. If you attached the Romer arm in the open areas between the bracing, then you are looking at the .010" accuracy that you speak of. At the facility where things are done the right way, I would comfortably say that +/-.0006" could be done with a smaller Infinite 2.0 Arm (if we had one), operator dependant of course.
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  • That may be, but I am not intersted in B89.4.22 results when in real world applications +/-.010 is what you get.

    We had a salesperson bring an arm out for a demo. I presented a part that simplified was a block with a tab sticking out one side. There was a hole in the tab. The Datums were the pretty obvious 3 mutually perp planes. I wanted to know how well the arm could report the location of the hole and the thickness of the tab. Both had been measured several times by myself and 3 others using CMM, microhite, a micrometers (for the thickness.). I asked for thickness first, they could not get closer than .008 to the actual thickness and their repeatability was equally horrid. I did not even bother asking for position after that.

    That is the extent of my personal arm experience, but I have conversed with many who use arms and CMMs for a variety of applications.

    Arms are great for some things. They can do what they can do. Tight tolerances they can not do.

    Oh, and I have not even gotten to the numerous reports of frequent encoder failure & costly replacement (In terms of both $ and downtime).

    Lastly in the interest of full disclosure, do you work for an arm company or a division of a company that makes sells arms or arm software?


    lol, I love this guy.

    Wes as someone who worked with DCC CMM's for about 8 years before messing around with PCMM's, here's my take on it. You are entirely operator dependant using a PCMM. Smaller probe shafts flex, and larger ones can't get into certain areas. The "cone" style calibration that is generally provided for tip calibration leaves much to be desired. In the world of PCMM's it is all about technique.

    Granted you can't hit .0002" accuracy with an Infinite 2.0, but I do believe you can hit the +/-.0006" stated above, but precautions need to be taken. If you need tighter accuracy, you have to stick with the larger probes (8mm to 15mm range) and they can't stick out too far. Calibration needs to be done to a Calibration Sphere, not a single point cone check (this is 20 hits with the probe sitting inside a cone, rotating the wrist around in different directions. here the stylus nominal diameter is used for calculations, and if the styli isn't exactly the number used you have problems). After this, holes need good sample hits, single points need good sample hits, the operator needs to be careful. Technique and Setup are also important at this point. Whether it's on a tripod or using the magnetic base, it needs to properly secured, and the relationship to the item being measured needs to held. At one facility, we have a granite surface plate with a 1/2" plate of steel bolted down to it on one end. The Arm is attached via the magnetic base to that plate, and anything being measured is clamped to the granite surface so that the relationship between arm and part never changes. That same facility uses a 30mm Calibration Sphere. At that facility, probe calibrations are within .015mm(.0006") all the time (edit: this includes a 3mmx20mm probe, which is the one that gets close to the .015mm), and that arm is a 3000 series (old). Another facility uses a 5000 series arm (newer but not a 2.0). They have a steel table instead of the granite surface plate, and use the cone method for calibrations. Their probe calibrations range between .040 and .065mm. The steel table is about 7'x7', braced with tubing around the outside and a cross throught the middle. If you attached the Romer arm in the open areas between the bracing, then you are looking at the .010" accuracy that you speak of. At the facility where things are done the right way, I would comfortably say that +/-.0006" could be done with a smaller Infinite 2.0 Arm (if we had one), operator dependant of course.
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