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Mitutoyo digital micrometer how to disassemble?

V Semionovas

Aluminum
Joined
Mar 24, 2007
Location
Sydney Australia
I was given a Mitutoyo digital micrometer 0 - 1" No. 293-766-10.
it is very stiff (probably was lubed with WD40 and left for quite a while)

What would be the best way to free up the thread?
How can I disassemble it to clean the screw and nut? :nutter:

Vladimir
 
There is a nut at the end of the thimble that can be removed. The micrometer should of come with a small wrench to assist in removing the nut. Once the nut is removed the thimble threads offs and the screw is exposed.

Mark Boucher
 
For me the tightness is usually some pitting solved by some gentle scotch brite.... though I did have one where somebody used a set screw to make a blade mic a go no go gauge and it mushroomed the rod ....
 
Vlad,
Mit digitals are a little trickier than standard mics. Yes you can remove the ratchet and the thimble as others have stated but my experience with these is that they have likely been dropped a little bit and the spring tensioner behind the pickup has moved enough to cause the tension.

Remove the 4 screws on the front of the digital display and stick them to a magnet so they don't walk off. If your mic has a detachable ribbon cable, unplug it and set the face aside. Many of the older Mits didn't have detachable ribbons. On the side closest the thimble there will be a pair of discs which are the pick-up/sending units. The one on the left will have a set screw which has a point on it that rides in a groove. To the left of it is another collar with a set screw. This collar sets the spring tension forcing the discs together. Alot of times it just needs to be loosened and repositioned to ease up the thimble pressure. Unless you have alot of time and patience do not remove any of these parts! -Mike
 
I just tried to adjust the discs as Mark suggested, but it didn't made any difference.
To remove the thimble, after removing the end knob, I can remove the knurled outer part of the thimble, but not the thimble itself, is it mounted on a taper shaft? If so can I force it a bit, or there's another trick in it? :confused:

Vladimir
 
Vlad,

loosen the ratchet mechanism but do not remove it. Hold onto the knurled part of the thimble with one hand and give the ratchet a light tap with a hammer handle with the other. This will release the taper. Then unscrew the ratchet and remove the thimble. -Mike
 
I was able to remove the complete thimble doing what Mike suggested, the thread looks clean, I loosened the anti backlash adjusting nut, but it still very hard to turn, looks like I have to do a complete disassemble to be able to see whats going on inside.
If I keep unscrewing the spindle, it cames to a stop, I dont want to force it, how should I proceed to completely remove the spindle? :confused:

Vladimir
 
You better get an expolded drawing of the mic before you start. More than likely the pointed screw next to the pickup disc that goes down into the slot is keeping it together as the slot doesn't go all the way to the end.

I am writing this down from memory and just as I typed the last line I remembered there is a screw UNDER the screw to the left of the disk. The top screw is a lock so the lower screw can't back out.
Before you go to complete disassembly remove the top screw and adjust the lower groove screw. It has to be far enough into the groove so that there is no backlash but loose enough to allow the spindle to pass by. The lower screw has a point on the end that fits into the groove to keep the disk timed with spindle rotation.

Post the complete part number of the mic. and I'll see if I can find an exploded drawing for it. I have a very old CD rom of parts lists. -Mike
 
Vlad,

Your mic was first offered in 1992 so it was on my disk. Here's the breakdown:
Mit293766-10.jpg


The double screws I mentioned are #2 & #3 in the #4 grouping. -Mike
 
Vlad,
Before you start take a look at the ground portion of the spindle that is inside the C portion of the frame. See if there are any tell-tale signs of damage to the spindle (bent). If you see very faint rings like faint screw threads near where the spindle enters the frame the spindle could be bent slightly, enough to cause the drag to be high. If it is bent bad enough you'll be able to see light between the anvils when they are closed and you hold them up to a light. If the spindle is bent no amount of cleaning will help.

Either way, it's a great learning experience. Have fun! -Mike
 
Micrometer fixed

Thanks for Mike (holescreek), I was able to fix my digital micrometer.

What I found was that somebody tried to remove the spindle without loosening the grub screws that ride in the little groove to drive the counter disk. It created a high spot on the edge of the groove, that high spot in turn scored the front guide bush, creating enough drag to make it hard to be used.



I stoned the high spot on the spindle, and made a copper lap charged with diamond compound to polish the inside diameter of the guide bush.

Just another question.
How the counter works? Is it an optical encoder?

Mike, thanks for your help.:cheers:


Vladimir
 
Vlad,

I can't help you too much on how the encoder works, but it isn't optical. My guess is that it uses electric pulses. The two phenolic discs are facing one another with the copper strips on each. The stationary disc acts like a switch supplying power on some strips and the negative side on the others. When the rotary disc turns against it it creates a pathway for the power to get to the negative side and create a pulse.

Congrats on the save. Don't forget to calibrate it before using it on anything important.

-Mike
 
Hello Mike.

I did check the micrometer using slip gages and it is Ok when I zero it closed and then checked it with various sizes up to 1".
Apart from the zero button.
When you say to calibrate it, what do you mean? is there any other adjustment in it?

Vladimir
 
If it read well and repeated on your gage blocks you are probably OK. Digitals are very forgiving due to the spring pressure holding the discs together. I guess it's just a reaction left over from the old days (pre-digital) to make sure a gage was calibrated before putting it back into service.

I still run all my repaired gages through the calibration routines, micrometers run the gambit of using ceramic gage blocks in specific steps to catch the spindle threads at 90 degree increments of rotation through the range and the anvils are checked for flatness with an optical flatness standard. Old school stuff. -Mike
 
Excellent thread!! I was able to fix a my micrometer with the information provided here, very clear explanation on how to adjust and disassembling the mike.

Is there any way to calibrate the digital read out? Checking with a 1" gage block after resetting the mike to zero and measuring the gage block I have a reading of 0.9952" in the display.

Thanks to all
 
I'm glad you got some use out of a 9 year old thread!

I haven't messed with these digital micrometers in awhile but I'd guess that the spring tensioner behind the encoder disc is jammed and the disc gap is opening as the thimble is turned, or just spinning. The digital readout only reflects what is happening with the encoder circuit, there is no adjustment.
 








 
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