Mitutoyo depth gauge problem

I bought a Mitutoyo .001" depth gauge from a booty for a pricely sum of £12. It came in a tatty box with 2 extension pieces. It seems very accurate on the main scale. This one has a digital readout also. Which does not seem to be working properly. It moves when the handle or whatever it is called , is rotated. But it stops & starts.

Has anyone had one in bits to see what is in there. I do not know if it is gear driven or just a friction unit. So if anyone has any experience with them please advise. Please do not reply with send it away for repair. I can live without the digital part but it would be nice to having it function properly. The model is BM008.

Steve.

Edited By Steviegtr on 08/04/2020 01:02:49

Do both readings show the same?

Hi Stevie

Have you tried a google search? I found a repair solution to a digital micrometer that way and Mitutoyo spares were really helpful with the required part.(sent me an exploded view diagram to help positively identify it)

On the digital version there is a collar with a grub screw with a tiny pin end which has to be removed before you can withdraw the spindle. If you don't do this the pin breaks off (sacrificial detail?) The pin is a very precise fit in a groove which runs along the spindle and on mine transmits rotational drive from the spindle to the digital encoder disc.

I wonder if there is something similar on yours which would account for the erratic movement of the counter. I could imagine a similar collar with a drive dog on it which moves the right hand dial and the collar being connected to the spindle in a similar way to mine. This arrangement allows the spindle to move lengthways while transmitting rotational drive from the spindle to the counter. If so my guess is that you remove the two screws from the top of the counter to expose the collar and grub screw behind. I am trying to remember if here was actually the grub screw and then a very short locking screw on top of that, I seem to recall that here was but could be wrong.

Ok so when I rotate the main adjuster to take a reading the Vernier scale is precise & smooth. The digital part will move & at times stop when I carry on turning the knurled shaft. It is hit & miss. I will do a google search before I delve in there. As it would be nice to have it working correctly. I wonder if as you say the pin has sheared off.

Steve.

If the worst comes to the worst, you can measure just using the graduations on the Thimble against the fiduciary line on the Barrel.

Ideally, it will read zero, on a good flat surface, with any of the measuring rods..

You look to have got yourself a good quality depth mic for a fraction the price of a new one.

Howard

Howard, as I said the Vernier scale works perfectly . I have tried it stood on a parallel. It is perfect zero. It was just that it would be nice if it all worked. Not necessary though.

Steve.

Micrometer scale!

Exploded View here if it helps.

Brilliant thanks.

Steve.

Yes. One day I will remember all these terms. Or maybe not.

Steve.

I ended up taking it to pieces today & as the drawing from the link above shows a grub screw with another under it.

Called a key screw. This screw was not in the slide notch on the spindle.

I ended up having to oilstone a watchmakers screwdriver to fit the minute screw. It took a couple of goes to get it right ,because when I put the grub screw back in & locked it up, it was then pushing the keyscrew a tad against the spindle.

Anyway all back together & it works great now. There must be a slight amount of wear on the brass gear as at zero it reads a quarter of a thou. See picture. If I backed the gear one tooth back it made it too far out in the other direction. Well pleased. Strange thing is it had a sticker from Oct 2019 for calibration. ???

Steve.

You approached a device with which you are unfamiliar, with caution, and found the problem and applied a solution.

And you shared your experience, so that the rest of us can learn.

Good engineering practice.

Howard

Cheers Howard. The thing was it was pointless sending it away to who knows where for repair. Luckily I was sent that link from Bandersnatch & I could then see the possible problem. I thought it through & came to a conclusion that it was a friction type of drive. Completely wrong as it slides up a slot. A very nicely made piece of equipment & quite heavy for it's size too. I do have the other 2 longer tips that fit in to go deeper. The box cut out in the foam dictated that is all that came with it. But the drawing shows a lot of lengths. So some must come more comprehensive. Regards.

Steve.

Well done, Steve

Howard summed it up nicely.

MichaelG.

Well done Stevie

sounds like it was indeed similar to what I was trying to describe- what I called a tiny grub screw with a pin on the end is what is actually called a key screw. And this then has a second retaining grub screw on top?

The collar as I called it appears to have a finely serrated gear on your mic, which is what drives the counter?

was the key screw damaged at all ? The tip of that component is very fragile and the one on my mic had been damaged which is why I replaced it. This might be why you find yours is not reading precisely. The profile of the top may not be sitting accurately in the groove as it might not extend down into the groove quite as far as it should.

if the tip has snapped off it will mean that the shoulder on the screw will rub on the spindle before the tip of the pin / key gets to where it should be within the groove.

These instruments are precision made and that part is really like a watch component. I suspect the pin/ key is designed to be sacrificial so it does not damage the spindle it keys into.

I think the damage occurs when someone tries to dismantle the assembly without first removing the key.
if yours is the slightest bit rough in use it may be worth getting and trying a new key from Mitutoyo.

with a quality instrument like that it is so nice to have it ‘spot on’!

Thanks for that John. The screw which I should have taken a photo of, did not have a point on it. It was square shouldered. The groove in the spindle was the same profile. The key was simply not engaged deeply enough. I ended up doing the setting twice. The 1st time I adjusted the screw so the spindle travelled it full length smoothly. I then refitted the 2nd locking grub screw, which must have put extra pressure on the key as it bound. I removed it & backed off the key screw by 1/8 turn & reassembled. It is now smooth throughout it's travel. You were correct.

I think someone has tried to screw off the spindle, which has the increment marks on it. This would have upset the key some how. Only a guess though. So 10 points to you for your diagnosis. Thanks for the info. Regards

Steve.

Thanks Steve

That info now stored in my mind - it is useful to know how these things are designed and put together as it helps when coming across a similar problem on a different tool.

I have the Mitutoyo micrometer with similar digital readout so that my well share the same innards as yours.

again well done sorting it

John

Steve,

Here's a link to the Mitutoyo micrometer instructions, that tell you how to reset/align the counter:-

Mitutoyo Micrometer Instructions

Nick thanks that is great. I was thinking there was wear on the brass gear. Just to the side of that gear was a screw ,which I did not disturb. That seems to be a locking screw for the gear. So fine adjustment can be made. I will have a look at that tomorrow. This forum is like the Oracle.

Steve.

Well to further add to the slight out of sink on the digital scale. Rather than rant on as to whether I managed to rectify it. There is a link here. A special thanks to Nick Hughes who gave me the link to the Instructions.

Trying to correct digital scale

Steve.