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View Full Version : Micrometer "feel"



Neil Jones
04-17-2009, 09:22 PM
Starrett tells me that after their micrometers are thread ground they are lapped.

I have some micrometers that are very smooth and have a great "feel" to them. I have others that aren't very smooth and that don't have the "feel / smoothness" that I prefer.

I wondered if anyone has every lapped a micrometer to make it smoother and how it worked out? If you did what kind of lapping compound did you use and what grit(s) did you use?

wierdscience
04-17-2009, 10:21 PM
I lapped one that had some rust damage to the threads.I used plain,white,cheap toothpaste.It has a mild abrasive in it and does a good fine lap with a little patience.

Mcgyver
04-17-2009, 10:25 PM
I can't speak to exactly how starrett laps the threads, but when stuff is lapped, its lapped against a lap - not its mating parts. doing that would just increase clearance making it a sloppy fit. lapping can put exceptional finishes on, but I can't see it being a trivial task making the thread laps especially when you can by a Starrett mic new for a hundred and something or on ebay for 20 - 30 bucks

Neil Jones
04-17-2009, 10:48 PM
I can't speak to exactly how starrett laps the threads, but when stuff is lapped, its lapped against a lap - not its mating parts. doing that would just increase clearance making it a sloppy fit. lapping can put exceptional finishes on, but I can't see it being a trivial task making the thread laps especially when you can by a Starrett mic new for a hundred and something or on ebay for 20 - 30 bucks

I'm told by Starrett tech support that they lap the mating parts of a micrometer together. Still trying to find out what they use for a lapping compound.

Mcgyver
04-17-2009, 11:06 PM
I'm told by Starrett tech support that they lap the mating parts of a micrometer together. Still trying to find out what they use for a lapping compound.

then i stand corrected. for lapping in general that's not the way to do it as you cant control how/where material is removed, although i guess if the compound was so fine it barely removed anything....maybe it is toothpaste they're using :D.

38_Cal
04-18-2009, 12:27 AM
Must be...my micrometers have never had any cavities!

David
Montezuma, IA

J Tiers
04-18-2009, 01:19 AM
Since the mics have a take-up for thread wear, lapping could be done with anything which won't "charge" into the parts...... It won't make the parts sloppy, since you can adjust them back into any desired state.

MTNGUN
04-18-2009, 11:38 AM
When I was young and dumb, i lapped a Craftsman mic with valve grinding compound.

Needless to say, valve grinding compound is waaaaay too coarse for lapping a mic.

Nonetheless, the mic worked much better after lapping.

Haven't tried lapping mics since then, but I've been tempted, because I have a set of import mics that are next to useless because the "feel" is so rotten. You can't get consistent readings because the "feel" is too rough.

First thing to try is merely drenching the threads with oil. That fixes a lot of them.

My knock-around shop mic (the one that sometimes gets dropped on the floor and otherwise abused) is a Horror Fright that was worthless when new due to the crummy "feel." I drenched it with Kroil and that, combined with several years daily use, resulted in a mic that works just as well as any name brand.

Paul Alciatore
04-18-2009, 04:42 PM
I would be cautious about lapping a mike. The fit of the threads is very important to the accuracy and repetability of the readings. In fact, I would not do so at all unless the nut was adjustable to take up any slack you may create.

On fine threads I have made, I find that a good quality grease (or oil) will improve the feel a lot and is removable if you don't get the results you want. Try that first.

SGW
04-18-2009, 06:17 PM
When I took a tour of the Starrett plant in Athol a few years ago, I actually saw them doing this.....

A row of guys sitting at benches, with a geared "speeder" setup they can clamp a micrometer in and turn the spindle quickly. They apply some very watery (though I assume it's really thin oil, not water) lapping compound, spin the spindle, test the "feel," take out the spindle and bang it on a lead block if it feels slightly mis-aligned...repeat until they're satisfied. They are FAST -- no more than a couple minutes a micrometer, as I recall. But they are truly hand-fitted. I would hesitate to do it myself. Those guys have had a lot of practice.

Neil Jones
04-18-2009, 06:31 PM
Paul, I've soaked a micrometer with a lousy "feel" with Starrett Tool And Instrument Oil that was recommended to me in another thread for something else and the "feel" is still horrible. Do you think changing to grease would help? If so what kind of grease... lithium based, synthetic, or?

moldmonkey
04-18-2009, 07:57 PM
I also would be hesitant but you could try diamond polish:

MCMASTER (http://www.mcmaster.com/ctlg/DisplCtlgPage.aspx?ReqTyp=CATALOG&CtlgPgNbr=2649&ScreenWidth=1280&McMMainWidth=873&sesnextrep=724544956449940)

MSC (http://www1.mscdirect.com/CGI/NNPDFF?PMPAGE=946&PARTPG=GSDRVSM&PMT4NO=62249074&PMITEM=03561032&PMCTLG=00&PMT4TP=*LTIP) has a better selection but only in oil soluble.

I used to do a lot of mold polishing with them and occasionally some lapping. A piece of brass and some brown or purple diamond will put a nice edge on a knife.:)

I would start with yellow.

wierdscience
04-18-2009, 09:21 PM
I would add here that the abrasive in toothpaste breaks down and becomes inert during use.It won't embed and forever be lapping away.

Neil Jones
04-19-2009, 08:12 PM
How would I go about lapping the anvil with diamond paste? Maybe make a lap out of of wood or brass and slide it back and forth over the anvil? I'd like a looser fit between the anvil and frame.

moldmonkey
04-19-2009, 09:19 PM
BRASS LAPS (http://www.mcmaster.com/ctlg/DisplCtlgPage.aspx?ReqTyp=CATALOG&CtlgPgNbr=2648&RelatedCtlgPgs=2429,2648&ScreenWidth=1280&McMMainWidth=873&sesnextrep=724544956449940) at the bottom of the page. They are expandable to compensate for wear. Or you make something similiar. We used copious amounts of steel ink remover to clean up diamond paste. Other strong solvents would probably work. Steel ink remover is the WD-40 of the tool room. It's always around and gets used for all sorts of things.

I personally would start with maroon Scotch-Brite, WD-40, and elbow grease. Great combo for cleaning rust from precision parts. Twist the Scotch-Brite into a cone and insert into the hole of the frame and twist away. I've had good success freeing up the auction special mics I tend to drag home with that method.

Edit: I just noticed you said anvil. Drill and ream a hole in a piece of brass. Drill & tap a hole off to the side and saw through into in the hole. Use a bolt to tighten it up as it wears. (Like a shaft collar)

Neil Jones
04-19-2009, 09:55 PM
Is steel ink remove Acetone? Where do you get it? I've never heard of it.

I'll try maroon Scotchbrite and WD-40 and see what happens.

I'll also make the "shaft collar" lap you described out of brass.

Thanks so much for the effort and the help, Jon! :)

chrsbrbnk
04-19-2009, 10:55 PM
I took a tour where they were making mic's they ground in the treads but I don't recall them lapping against themselves
they lapped in the anvils on a disc about 1/4" thick and about a foot in dia I think it grabbed on by the spindle with it open about 3/8" then the fixture slid back and forth to lap both sides parrallel the way they beat into intial alignment the brown and sharp tubular mic's was one of those let down moments kinda way to primitive for a tool like that .

Paul Alciatore
04-20-2009, 03:33 AM
Paul, I've soaked a micrometer with a lousy "feel" with Starrett Tool And Instrument Oil that was recommended to me in another thread for something else and the "feel" is still horrible. Do you think changing to grease would help? If so what kind of grease... lithium based, synthetic, or?

Neil,

Since the amount of looseness in the mike is unknown, you will have to experiment. Way oil is thicker and may work well. It would not hurt anything to try it. Other, thicker oils are available. Definitely try oils first. There are so many types of grease it is hard to recommend one. Perhaps a lighter one for a first try as too thick would make it hard to turn. Or perhaps a silicon grease would be a good first try in that department. I would definitely stay away from motor oils or inexpensive grease intended for automotive use. They can have additives that can leave stains if used for some time.

You may have to lap to get the feel you want. I would just save that for the last option as it is hard to reverse if it goes too far.

Neil Jones
04-20-2009, 10:02 AM
"Since the amount of looseness in the mike is unknown, you will have to experiment."

It's not loose. It's tight.

ptjw7uk
04-20-2009, 11:37 AM
In the UK I would use 'Brasso' metal polish as this contains a very fine abrasive. Used in metallography to polish metal samples before etching.(well in UK anyway)

Peter

John Garner
04-21-2009, 05:56 PM
Years ago, I lapped a Moore & Wright metric micrometer that had the worst "feel" I've ever encountered -- intending to either cure it or kill it -- using the dust left inside an empty can of Timesaver-brand green-label compound I dug out of the trash.

I mixed the Timesaver powder left inside the can with two or three drops of hydraulic oil to make a soft paste that I divided between the micrometer nut's internal threads and the spindle's external threads, reassembled the micrometer, and ran the spindle both ways through its full travel about ten times. Took the micrometer apart again and added a couple of drops of new oil, reassembled, and ran the spindle another ten roundtrips, repeating the disassemble, oil, lap cycle maybe four of five more times before disassembling the micrometer, cleaning the residual oil and grit out with paint thinner and cotton swabs, oiling, reassembling, and adjusting the micrometer.

The "feel" was vastly improved, but still on the rough side. So I disassembled the micrometer again, cleaned out the oil, lubed the made and female threads with moly-disulfide paste, reassembled, clamped the thread-fit-adjustment collar as tight as I could make it, and exercised the spindle another ten-or-so roundtrips to burnish the newly-lapped threads. Followed by another disassemble, clean, lube, reassemble and adjust cycle.

At that point, I was reasonably satisfied with the M&W's feel and used it for a couple of years before giving it to a fellow student who'd had his tools stolen.

Since then, I've rehab . . . nah, let's just say "habilitated", a couple dozen micrometers imported from the far east using a different technique. Most of this class of micrometers I've encountered have three common problems: 1. they are packed with preservative grease, 2. the female thread is often burred where it is slotted to provide "collet action", and 3. the threaded spindles are banged around after thread grinding.

Taking these problems one at a time:

1. Disassemble the micrometer fully, soak it in mineral spirits or kerosene, scrub with a nylon-bristle toothbrush and "itty bitty bottle brush" (if you have one), and finally blow out the inside of the micrometer housing and internal threads with a spray-can of carburetor cleaner.

2. Working under magnification, remove burrs on the internal thread using a dental-pick-type tool and/or needle file.

3. Chuck the unthreaded end of the micrometer spindle in a drill press, lathe, or milling machine spindle, run the spindle at some moderate several-hundred-RPM speed, and press a medium-grit diamond hone against the major diameter of the thread while running the hone along the micrometer threads axially until the clicking of the hone stops, signifying that the major diameter of the honed micrometer thread has been reduced enough to remove the damaged thread crests. Then remove the honing burrs, either by Scotch-Briting the micrometer thread or lapping it between a couple pieces of grit-charged wood.

Clean and dry the individual pieces, deburring as necessary, and then lube the inside of the female thread and the outside of the male thread before reassembling and adjusting the micrometer.

I generally lube micrometers with a light hydraulic oil, but Singer's Sewing Machine Oil and Dexron ATF work about as well. But . . . a few weeks ago I needed to clean and oil a micrometer that had been dropped into a mud puddle. The only light oil immediately available was from a spray can of Liquid Wrench #2 (in the teal-blue can), and I'm impressed with the improved feel of that micrometer . . . so far.

Neil Jones
04-21-2009, 11:09 PM
Printed this out, John. Thanks!