How do Mitutoyo Profilometer Stylii work?

Zahnrad Kopf · May 1, 2018

Have a Mitutoyo SJ201 Profilometer that has a bad stylus. It was munged up when I got it, but I was able to get it freed up and mechanically functioning again. The issue however, is that it does not "read" correctly. It is giving results of approximately just under one half of what it should. I have tried adjusting the various adjustable thingies ( technical term ) I found inside it, to no avail.

What goes bad in these things? Are they repairable? Is it even worth it? How are they adjusted at the factory?

My hope is that I can adjust it to read correctly. Calibrate it, if you will.

Thanks.

specfab · May 1, 2018

I would examine the actual probe tip to start with. If it is damaged (truncated, rolled-over, or otherwise misshaped), the results will likely be less than expected because the stylus is too large to get down into fine finish grooves. I believe those units had (have?) either 2 um or 5 um stylus tips. Electronics could also be screwy, but I would make sure first of the fundamentals like contact point condition.

Zahnrad Kopf · May 1, 2018

Already did. Tip is seemingly okay. Very interesting how they make them, too. Frankly, not all that clean and professional looking, either. Whatever works, though... The actual physical stylus tip is a small piece of round stock approximately 1mm in diameter, threaded on one end ( for insertion into the lever arm ) and with either a reduced diameter or a smaller piece inserted into the end. Hard to tell right now as my higher power microscope lens is put away at the moment. However, the actual working end is then given some 90° grooves ( apparently filed from the looks of it ) into four quadrants. Think of placing a piece of round stock on end, and presenting the corner of a 90° file in a horizontal and vertical line forming a crosshair for a shallow amount. That is what it looks like.

Anyway, that part appears okay. This is definitely an adjustment of some manner. I have fiddled with it, but am working blindly in ignorance so am not getting good results.

Hence the inquiry...

specfab · May 1, 2018

Just FYI, that is (should be) a diamond fixed on the end, carrying the prescribed tip radius. The diamond mounting is probably what you are seeing with the grooves. Grooves very likely done by tiny white-gloved hands with a nano-file....

Zahnrad Kopf · May 1, 2018

LOL!!!! Good to know... Thanks!

Mud · May 1, 2018

What model is it? I have one that is complete and turns on but the stylus doesn't move. I don't think the stylus is threaded though.

Zahnrad Kopf · May 1, 2018

Hi Mud! It's a SJ201. The stylus actually just pulls right out of the probe housing. ( it's a plug )

Ziggy2 · May 1, 2018

Mud said:
What model is it? I have one that is complete and turns on but the stylus doesn't move. I don't think the stylus is threaded though.

There is a very small lead screw driven by a servo motor. When the sensor unit is dropped on its stylus end, the lead screw thrust bearing gets messed up so the servo motor does not have enough power to move the stylus properly.

There is also an accelerometer attached to the stylus that actually reads the surface finish data that is combined with the servo motor velocity signal. Electronically pretty nifty.

Rather robust units relatively speaking unless you drop it on the stylus end pointed down. Problem is that seems to be the only orientation that the instrument ever contacts the floor in. Sort of similar to why does the buttered, jelly or peanut butter side of bread always fall face down.

I have had Mitutoyo repair them before. Kind of a wash. You can buy the complete sensor, cable, and stylus for like $700 or you can get it repaired for maybe slightly less if not to much is wrong.

The chances of damaging the unit varies exponetially with how important it is to be available. I used to keep at least two spare transducer units on the shelf for the careless guys. Seemed to actually reduce down time and costs by having the spares available.

Zahnrad Kopf · May 1, 2018

Thanks Ziggy2. Had me laughing the whole read. And I definitely needed that, today. Second Monday in a row. Spot on in every aspect.

Ziggy2 said:
There is a very small lead screw driven by a servo motor. When the sensor unit is dropped on its stylus end, the lead screw thrust bearing gets messed up so the servo motor does not have enough power to move the stylus properly.

There is also an accelerometer attached to the stylus that actually reads the surface finish data that is combined with the servo motor velocity signal. Electronically pretty nifty.

Rather robust units relatively speaking unless you drop it on the stylus end pointed down. Problem is that seems to be the only orientation that the instrument ever contacts the floor in. Sort of similar to why does the buttered, jelly or peanut butter side of bread always fall face down.

I have had Mitutoyo repair them before. Kind of a wash. You can buy the complete sensor, cable, and stylus for like $700 or you can get it repaired for maybe slightly less if not to much is wrong.

The chances of damaging the unit varies exponetially with how important it is to be available. I used to keep at least two spare transducer units on the shelf for the careless guys. Seemed to actually reduce down time and costs by having the spares available.

Conrad Hoffman · May 1, 2018

I don't know anything about that unit, but it's usually possible to measure the stylus profile by scanning over a new razor blade. Probably have to mount the blade between two pieces of metal so everything is within the vertical range of the instrument. A sharp razor blade has a radius smaller than the typical stylus, so it will profile the stylus. Of course, you have to have a stylus tip present to begin with.

Zahnrad Kopf · Jun 24, 2018

Reviving this thread to ask -

Does anyone know definitively if probes from the 301 and 401 profilometers will work in a 201? I ask, because there are seemingly scads of probes available but 99% of them are for the later models and I am ignorant to their interchangeability.

Thanks.

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