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View Full Version : Using a Tubing Micrometer for General Purpose Measuring?



spongerich
05-07-2013, 12:31 AM
I picked up this Mitutoyo 295-313 Tubing Mic at an estate sale a few weeks ago.
The digital dial was .075 out of sync with the actual measurement.... but I figured for $5.00, I couldn't go wrong.

After using it a few times, I REALLY liked the digital readout. My eyes aren't as good as they used to be and I found it incredibly convenient... or it would be if it were actually accurate.
Tonight, I decided to take it apart and see if there was any way to correct the error. It turns out that the little housing that holds the dials has some adjustment. I was able to move it enough to disengage the little gears that drive it, then I was able to match the reading on the barrel and then re-engage it. Now it's right on (well, within half a thousandth)

Is there any reason not to use this mic for general purpose measuring? The end of the spindle is flat, but the anvil is spherical. I did some playing around measuring some bar stock and some Jo blocks and it seems I was able to get measurements that were pretty close to what I got with a "normal" mic.

I'm not making any parts for nuclear reactors, so a few thousands is more than close enough for 99% of my projects.

http://i1019.photobucket.com/albums/af320/rmaracing/mitu295-2.jpg
http://i1019.photobucket.com/albums/af320/rmaracing/mitu295-1.jpg

becksmachine
05-07-2013, 01:35 AM
Want to double your money? I would give you $10.00 for it??

;)

If you pull that plastic cap off that is right next to the spindle lock knob, you will uncover two set screws that can also be used to adjust the digital read out. One screw extends into the groove that is ground into the spindle to drive the digital counter. The other one locks a drive gear to the aforementioned drive screw, and allows infinite adjustment of the digital counter in relation to the barrel/thimble graduations.

As for using it for general measurement, it might be difficult to achieve the proper feel on the OD of a round part, but for 2 flat surfaces it should be fine, if a little more flexible than a standard c-frame style.

Dave