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Calibrating Mitutoyo 0-12" depth mic set

MyLilMule

Hot Rolled
Joined
Jan 5, 2021
Location
Ohio, USA
Forewarning: I am a hobbyist. I lack knowledge and experience in many things but have an above average capability to learn.

My son is interning at a plant that has a small machine shop. They had several of these, brand new, never opened, that they were tossing in the garbage. He managed to save this set for me. I checked the 0-1" pin with a known reference and it was a good .040" off from what any of my outside mics read. I'd like to have them calibrated. But I don't know where to begin or what it would cost. If it isn't cost prohibitive to take them or send them someplace, I don't mind doing that. I'm $0.00 into a $400 set of depth mics.

I do not have a set of gauge blocks to try this on my own. If it's easy enough to get reasonably close (+/ .001" is close enough for what I do), maybe I will just find a set of gauge blocks and do it myself? Or is that a fool's errand?

I'd appreciate some measured advice from those more in the know.

Thanks.

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I'd firstly make sure you are properly seating the shaft, and using the smallest rod confirming that the zero position is reading zero. The barrel can be adjusted with the small spanner tool if it isn't spot on, and that sets the baseline for all the other rods (they are calibrated to the same offset.) If the zero is set correctly and you are getting errors when measuring a known height, then your known hight, technique and reference surface need to be re-examined. It is easy to get unintentional errors when measuring these small distances, and the tool isn't the first thing to suspect.

They come from the factory calibrated, and in my experience (I have 2 sets of these) time will have had little effect on them if they were kept in the sealed bags. Put them back in bags with fresh anti corrosion paper. If you really want to verify or calibrate them, (again, likely a waste of time as these are intended for .01mm accuracy and they are essentially unused) then the usual fashion is to create a stack of the less common 'square' type gauge blocks that have a central hole in them. I have a set, and found it makes keeping everything straight very easy, but they are not cheap to buy and not as broadly useful as standard blocks.

Also, that degraded foam can sometimes badly damage the finish of the unit. Make sure all of it is removed and put in some wool or polyester felt (and more anti-corrosion paper.)
 
*I'd* firstly smack the shite out of anyone who would throw those in the dumpster.

Then, I'd use the wrench that should be in the box to adjust the small nuts on top of the rods. That will move them up or down as needed. Not sure how the heck someone got one .040" out of whack unless they were just turning the nut for fun. Baka has described the rest of that process pretty well. Also, I agree about getting all that foam out of there. Some of that stuff can outgas some pretty corrosive gases. I'd get rid of it just to be safe.
 
I. Am. A. Total. Noob. 😂🤦‍♂️

I went out to the shop just now to check if the rod was seated as @Bakafish suggested. Ooof. The thimble cap was not fully seated. Once I did that, the 0-1" rod was within a few tenths of .000" when set on a flat reference surface. I'll pick up a grade B set of gauge blocks sometime soon and do my best to check the rest of the rods. I have a small set of the round spacer blocks with the threaded hole in them for stacking.

I already removed all of the foam. I intend to find some new foam today. I'll have to locate some anti corrosion paper to lay on top of them - not sure where I can source that or if I can make it.

And this was just one of SEVEN of these sets that were being thrown away. They were all rescued by the other employees.
 
Glad you got it worked out. Really a user error is the best option because you've fixed it with a little education instead of a $$$ calibration.
For gage blocks, and I hesitate to say this, the $120 set on Amazon or wherever will probably do you just fine if a tenth here and there isn't important to you.

I have a 112 piece metric grade 0 (Grade A for you inch folks) Mitutoyo set, which is a work of art IMO, and a made-in-China-brand 80ish piece grade B inch set. At least 8/10 times I or someone around me needs gage blocks (in its self a rare thing) the grade B set comes out. The grade B set is visibly cheaper, but it gets the job done. If nothing else the cost of replacing the entire set is little more than replacing a single block in the other set, which is reserved for trained individuals at the rare times it actually matters.

Echoing the above, new foam and VCI paper. VCI paper does have a finite lifetime, even in a semi-sealed environment (and very short if left in the open), so I've taken to leaving a camphor block with a corner barely cut open in any drawers that have metrology gear in them. It's completely stopped my corrosion issues.
 
Speculation unsupported by known information -- CMMs are wonderful, amazing instruments, but widespread availability and use of CMMs apparently leads to this kind of behavior (throwing away perfectly good measuring tools). You got a good deal, for sure;-) It would be interesting to know the reason behind chucking multiple unused sets of depth mics into the dumpster.

Good choice to get yourself a set of gage blocks. That cost will be a good deal less than sending the depth mic set out to a calibration lab even once, and they will also be usable for many other tasks.
 
I just went through this with a 0-6" Mitutoyo 329-711-30. I found using Hoke blocks (square gage blocks with a hole in the center) over my surface place the easiest way. Undo the set screws on the larger end piece and use the smaller end nut to push it down if the reading is high and rotate it out when the reading is negative, both at the nominal zero. Always mount it and tighten up the spindle as that's pushing the 2 end bits together. I didn't tighten the setscrews until I was somewhere near -.0003 as it seemed that tightening gave about that much offset. Most I was able to get near .0001. Maybe if I'd spent another hour per rod I could have hit 0 on both the mechanical and electronic zeros at the same time.

(I had to recalibrate as the rods didn't belong to the head - the head was a $7 purchase at auction and $50 to repair the innards, the rest of the kit was an eBay purchase. Still and all about $100 for the whole set, I think that's pretty good.)
 
This doesn't really need to be posted but for those new to measuring tools perhaps this will be of some help. I have a set of depth mic's and was careful about checking/setting the rods against a standard made for depth mic's (Spiral Step Tool) to verify accuracy. After swapping rods out several times for different jobs I noticed a discrepancy when checking a rod against a standard. I thought it odd as I had set all the rods at one time and was careful with the set. As I grabbed the adjustment wrench it occurred to me that something else was amiss. I carefully cleaned everything, this time taking care to clean the surfaces the rod seated against and then running some paper between both seating surfaces, much like doing this on a 0-1 mic. The discoloration on the paper told the story of a thin film of grease/dirt/grinding dust coming off my fingers and lodging on the rod adjusting cap. Re-assembled and the reading was right where it should have been. Crud gets into/onto everything. Lesson for me: Clean everything very thoroughly before reaching for the adjustment wrench. Hope this helps someone.
 
Good tip for those unaware. I have always made it a habit to clean the mating surfaces of every measuring tool that comes apart like this. Every time I change the rods or extensions. Generally just use my work shirt. And yes, they quite often leave a smudge - that greasy dirt does indeed get everywhere.
 
I think cheap jo blocks are a great investment for a home shop. They come with an inspection report that lists the "exact" sizes and that sheet it what makes them a good value. I checked a few with the CMM at work and they were close enough to the listed size that I didn't check the rest. If you have a stack of blocks and you know that the 1" is .0002 big and the .500 is .0001 small you can do just as good a job inspecting a feature or setting a gage. When tenths matter just pick blocks based on the inspection report, doesn't take much longer.
 
I usually explain the dust/crud thing like this:
Do you want it to be accurate to a tenth?-yes
Can you see something that small?-no
Can you see dust?-yes
->The dust is bigger than your acceptable error, clean it off!

Then again, I won’t use a pair of calipers on a +/- 1” part without checking their zero and closed jaw position against a light out of habit.
 
Then again, I won’t use a pair of calipers on a +/- 1” part without checking their zero and closed jaw position against a light out of habit.

You and me both. I would say it was a form of OCD, but it actually serves a legitimate purpose. I clean the jaws on a caliper just about every time I pick one up.
 








 
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