Calibrating a PH-350 Mitutoyo Comparator 1

[sigmex]

We use a Mitutoyo optical comparator model PH-350 in our Q.A. dept. However, we do not have any reference material, i.e. user's manual for it. We need to understand how to calibrate this comparator. I have checked on Mitutoyo's website, but did not have any luck finding any documentation for comparators there. I also have googled for this information, but no luck there as well. So, anyone out there has knowledge/documentation/or links or contacts for such information, it would be greatly appreciated if you would send a reply.

Thanks in advance.

Mark

 

[macengineering]

Mark, I see your question is over a year old, but maybe you're still having a problem calibrating your PH-350. Chances are, it hasn't fixed its self.
Several years ago I owned a PH-350. They're one of the best optical comparators on the market. I own a small aerospace machine shop and use the comparator daily. I had never had a problem with my parts being rejected for out of print sizes or forms. I check a lot of O-ring grooves, thread forms, lead angles, etc. And my customer is very fussy. It's got to be right. No exceptions.
One day, I didn't have anything (important) to do and I was messing around with the comparator to see how accurate it was. Wow, this thing was off by, what to me, was mile. On a linear measurement of one inch, on the X direction, I was off by .0015. I was measuring the diameter of a 1.000
dia. pin. The digital readout was saying .9985. That's not even close! Over longer distances, the measurement was worse. But about the same discrepancy per inch.
Inside the Mitutoyo Digital Readout box there is a DIP switch. The owners manual talks about using the switches to correct any error. The only problem is that the most error the DIP switches can correct for is two tenths per inch. That's .0002. In my case, I had over 7 times that amount of error. And to make matters worse, when I talked to the Mitutoyo people in the Los Angeles office, they said the two tenths correctability is over the entire length of the digital scale. Not two tenths per inch, but per what ever the length of the glass scale was. I think it was 10 or 12 inches. Either way, I was way out of the ball park.
So...What I did was try to change the length of the mirror and the focal length inside the cabinet. This was a big mistake. Don't do this. It made matters much worse. The mirror position is set at the factory and if the position should change like mine did, you don't have the proper equipment to readjust it correctly. I ended up taking my comparator to the Mitutoyo facility in City of Industry, a suburb of Los Angeles. I think it cost me around six hundred dollars to have it re-calibrated. Before I took the thing up to Mitutoyo, I had one of the field service techs come out to shop to "re-calibrate" it. The way the service tech does this, is he checks the digital read-out scale electronicly. He did this and said everything was "just like new". So then I had him check a part. Actually, a one inch round pin. Check the diameter to see if the digital readout will say 1.0000. It didn't. Once again, it said .9985. This guy must have rechecked the scale a dozen times. And every time he measured the one inch pin, it said .9985. That's when I took it into Mitutoyo's repair facility.
So, Mark. Don't make the mistake I made by trying to adjust the mirror. Let Mitutoyo fix it.
Thanks, Rob Macfarlane