Trouble with Diameters

A) calibration of the machine B) calibration to a sphere of the probe C) ensuring good technique and positioning of the probe in the hole D)arc of the circle your trying to measure... depending on your tolerances all of these variables can be a factor plus some I've probably forgotten... I use a romer arm exclusively (small shop) and tend to use the measured romer arm results as an estimate and then check them with gage pin, inner mic, etc.. as a sanity check depending on my tolerances.

First off, yeah, good luck getting sized on sheet metal with a Romer. It isn't so much the hardware as it is the fleshware. Trying to hold that probe on the shear while triggering the probe.....

What size holes are these? Are they small enough that you can use the 1-point hole method? You need a probe that it bigger than the hole, and it requires you to measure a plane around the hole, then you hold the probe on the hole, and it will calculate based on where that measured plane intersects the probe.

I'm sure I can apply that to a few parts, but there are times when the diameters are larger than the probe. I only have 3mm and 6mm

yes I only work with Romer arms aswell, our shop isn't to small tho. this is off topic but have you had experience measuring parts with the laser??j

Where is your master 19.05 probe? (or whatever size it is, about 3/4")

no, we don't have a laser... wish my owner would spring for one but I don't see that happening this century. As far as the one point method... I use that all the time and it's great for position but not so much for size. The hole has to have an absolutely perfect edge and the "plane" that you measure has to be nearly perfectly flat to get an accurate diameter size since the software uses math of the probe size and plane position to get the diameter. Any variation at all will throw (and I use English standard inches here) the diameter up to several thousandths just depending on the severity of the defect on the part. Even deburring a part can throw the size/position a bit as a dotco (sp?) will leave a small chamfer along one side or imperfect chamfers due a concentricity issues. Using a hand whip for deburr will really cause havoc.

I was recommended to not use it for probing. I only use when I go to calibrate the other probes

ok and all this stems from an Engineer asking me why the romer can not measure diameters properly, kinda hinting that I may be doing something incorrect etc. My argument was that it is very difficult to measure diameters on sheet metal parts, and the other was that when I measure the diameter of a hole with the biggest allowed pin gauge, it will drop 70 to 80% down into the hole and then get caught up, I think its due to the holes being tapered and not the machine accuracy

I run into that all the time (thus using the gage pins etc.). I don't have a probe long enough for many holes firstly so gage pins are the only way to do it plus if a hole isn't supposed to be tapered (cone) it's difficult to get those results... or at least I haven't figured out how to. No training other than the guy that I replaced showing me a few things so I'm OJT all the way... And there is a difference in the measurement options too... least_sqr, Min_sep, and max_inscr all measure in different ways and I use them depending on what I'm trying to do... If I think I have a taper Ill create a cylinder, use the max_inscribed option, do a constructed circle with the cylinder and plane it intersects and that usually gives me position and a general idea of what the hole really is... Or I just do the gage pin thing to see how much taper there is... plus the romer won't tell you if there is a lip on one side of hole or not on thicker parts... like if the reamer didn't go quite all the way through or was slightly tapered itself, which makes a difference on tight tolerance parts (a few tenths)

Yeah I attended the Romer Arm course at hexagon but most of it has been OJT and I've only been at it for about 5 months.