Micrometer Reading Help

seal killer · Post by **seal killer** » Mon Oct 12, 2009 6:43 pm

All--

For a long time I have been struggling to read a manual micrometer. Although I have a good electronic 0"-1" outside mic and an electronic Fowler depth mic, I also have several manual micrometers that I do not trust myself reading.

There is a picture below of an old Lufkin Rule No. 1641 with a 0.250 plus plug gage in its jaws. Does the micrometer read 0.250 plus about 0.0006" or 0.0007"?

Thanks!

--Bill

Nosmo · Post by **Nosmo** » Mon Oct 12, 2009 6:50 pm

looks like 0.2506" to me.

Jose Rivera · Post by **Jose Rivera** » Mon Oct 12, 2009 7:20 pm

Calibrated eye !!!

Agree, but unless the micrometer has the tenths vernier, .0006" is anybody's guess.
A tenth even the vernier some times is hard to see.

SteveM · Post by **SteveM** » Mon Oct 12, 2009 7:22 pm

If you trust the plug gauge, then it's time to adjust the micrometer.

You should have a wrench that fits in a little hole in the inner barrel to turn it.

Steve

seal killer · Post by **seal killer** » Mon Oct 12, 2009 7:59 pm

Nosmo and Jose and Steve--

Ha! I knew I would get the answers!

I "inherited" the micrometer--along with a couple more which I have not cleaned up, yet--from my brother-in-law. (The estate sale junkie.)

When the thimble is in the gently closed position, it reads about 0.0004" or 0.0005". Picture below. (If I can adjust it, then I think it will be a good instrument, since I trust the plug gage . . . I measured it with two other mics, one of them electronic.)

Steve, the hole you mentioned is present and a closeup of it is below. I can't tell from my picture what kind of wrench might fit. Is it merely a small allen wrench? (Sounds too easy, but the INNER hole looks like the smallest allen wrench in the world. I'll clean that teeny tiny hole a bit better.)

--Bill

Post by **GlennW** » Mon Oct 12, 2009 8:07 pm

Bill,

You need a spanner type wrench. The drum (the part with the long horizontal line on it) rotates to align it with the ) mark.

I just got home or I'd post a pic of the little spanner required. (It's at the shop)

kenh · Post by **kenh** » Mon Oct 12, 2009 8:08 pm

Is the gage and the anvils clean?

Post by **GlennW** » Mon Oct 12, 2009 8:14 pm

Well, check this out!

http://www.jjjtrain.com/vms/measure_mic ... ic_06.html

seal killer · Post by **seal killer** » Mon Oct 12, 2009 8:55 pm

Steve and Glenn--

Glenn, I am glad I just took a VERY high res picture of that little hole, anyway, because it has no socket.

Steve, I wonder what its purpose may be? (Picture below.)

Glenn, I have a couple of those spanner wrenches laying around. Perhaps one of the wrenches from one of my other mics might work. I would sure like to restore this Lufkin 1641 to accurate functionality. (I bookmarked the site. Thanks!)

--Bill

seal killer · Post by **seal killer** » Mon Oct 12, 2009 9:22 pm

kenh--

Yes . . . they are finger-wipe clean. But, I will check them again. I am still in the process of cleaning the instrument.

--Bill

Post by **Harold_V** » Mon Oct 12, 2009 11:30 pm

seal killer wrote:kenh--

Yes . . . they are finger-wipe clean. But, I will check them again. I am still in the process of cleaning the instrument.

--Bill

Not good enough, Bill.

A very good way to clean the spindle and anvil, all at the same time, is to insert a piece of paper (no ink), and snug the spindle--but not too tightly. Withdraw the paper. Do it more than once if you find they're still dirty. If the surfaces are in good repair, they will be spotless.

Insure that the mic is at 0 with your feel. The mic should turn freely, and will have a definite feel to it when the two faces come in contact. Try to emulate that feel when you take measurements. That's what makes a micrometer reliable----knowing what constitutes being tightened properly.

Harold

Jose Rivera · Post by **Jose Rivera** » Tue Oct 13, 2009 12:30 am

"This hole has obviously been used, but there is no socket functionality that I can see."

Bill, the barrel of the mic is pressed-fit.
The hole for the spanned is so you can force-twist the barrel to match the thimble's number zero.

If you remove the spindle (which is easy to do by just unscrewing it all the way), you'll see a little ring that is there so decrease or increase the tightness of the threads over the spindle's.

Most mics have the spindle attached to the thimble by a screw which some times is part of a feel-ratchet and a taper.
This is another way that one can zero the thimble without the spanner.

You'll have to loose that screw and then tap it (carefully) with a soft hammer. Usually the spindle will let loose from the thimble.
If not, then you may have to remove the screw and use a drive pin punch being careful not to damage the threads.