Dial Caliper Adjustment

You got dirty teeth. You need to brush. (no... really)

A chip has caused the pinion to skip teeth.

You can't _easily_ get the pointer back, except perhaps by running the pinion over that chip a few times in the hope that it restores.

But you can get the chip(s) out so they don't cause it to happen again -- then take care to keep your calipers meticulously clean -- I don't mean _clean_ them frequently, I mean make sure they don't ever get dirty. Don't lay them where errant chips and filings can reach. Don't put them down on chip-covered surfaces.

To clean out the rack, the simplest way is to use a very fine embroidery needle, and _gently_ rake out each tooth. Use a magnifying glass, and make sure every one is clean of chips.

Then, don't ever get them dirty again.

There are fully-shielded calipers available. Most of the lower-end ones have a sliding shield, but it doesn't cover all of the rack all of the time.

Decent quality optical (digital) calipers aren't prone to this sort of failure, but you can damage the scale if you get chips between scale and slider.

LLoyd

Well, there is a way: Use an unrolled piece of flat watch spring and slide it between the rack and the pinion inside the head, and cause the pinion to skip a tooth in the opposite direction. The pinion is spring-loaded against the rack, to prevent backlash, and will tolerate this without difficulty.

I've also taken a bought-used Mitutoyo dial height gage apart and cleaned it. Reassembly was not difficult. Resembles working on a mechanical clock. The main advice is to work on a clean table over a large pan lined with fabric (so dropped items don't bounce), so you don't lose any parts. It's also good to vacuum the floor before starting, so you have a prayer of finding dropped parts.

Joe Gwinn

Yur crazy, they actually make a tool for this. Little thin rod you stick in the back end of the device and hold the pinion up. Takes like two seconds.

yes keep em clean.

I prefer Etalons, but they really hate chips

A cheap white bed sheet folded once or twice to size is good for this, & makes stray parts really easy to see.

Excellent advice, Joe.

Not _completely_ crazy, just a little. Most folks don't have that tool. They buy a bottom-of-the-line dial caliper, and wouldn't even think to look for the adjustment tool.

The watch spring idea is probably more in line with what the average guy will have just lying around. But selectively "skipping" over the vagrant chip works most of the time, and requires no tools at all.

You don't have to get the needle precisely at 12:00 o'clock, just close -- it's only a matter of convenience for reading. The bezel will set to zero anywhere.

LLoyd

THE tool for most is a little key-shaped item made out of shim stock, the small end is a little less than rack width. Most of the dial calipers I've seen have the pinion spring-loaded, you take above item and press it into the rack/pinion interface area to disengage the pinion, then mess with the thing until the pointer is about where you want it. Higher quality dial calipers include the tool, it's maybe 5 or 10 thou thick, usually under the foam in the case. Brush your rack's teeth too, you've got a chip in there somewhere.

Stan

And once it's fixed a trick and old time machinist taught me to lessen the chance of chips falling in or help chips fall out is to always lay it face DOWN against it's crystal(plastic?) face.

Oh and for those of you who are the dissasembly kind of people, my father was a photographer and repaired cameras. He sealed and painted white the big file drawer in his desk. When it was time to dissassemble a camera or shutter he'd stick it and his hands in the drawer and close it as far a he could, THEN he'd take it apart... if any parts fell out or springs flew away they'd stay in the drawer :-)

--.- Dave

Remove the bezel clamp screw and plastic clamp, and there is a small slot moulded in the back of the face housing. Find a length of stiff wire that will push in to this slot and lift the gear clear of the rack, then set the dial to zero and close the caliper, remove the wire and job done. This is how its done on the Mitutoyo calipers i have used unless yours is different. Paul.

Hell..you dont have to have the needle at 12:00 at all. As you say..its a matter of convience for the anal retentive.

Gunner, ducking and running

"Liberalism is a philosophy of consolation for Western civilization as it commits suicide"

- James Burnham

On Wed, 21 Mar 2007 16:35:16 GMT, with neither quill nor qualm, "Dave August" quickly quoth:

Yeah, who -cares- where the little dial is since you won't be able to read it through the scratched bezel anyway?

------------------------------------------------------------- give me The Luxuries Of Life *

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Ya know Larry, I though that too.

But I figured my old time machinist friend who worked for Rockwell and made parts that put men on the moon knew what he was talking about.. the face on his 30 year old Starett look just fine, I'm going on 15 years now with same caliper and it's as clear as the day I bought it.

I'll take a few scratchs on crystal over a trashed rack and pinion every time :-)

--.- Dave

Mitutoyo generally supplies, with the caliper, the tiny tool that permits reorientation of the pointer. It's that tiny brass finger you thought served no purpose and threw away.

Harold

Thanks to everybody for the suggestions, especially to Paul. It turns out that the slot on my calipers is on the top of the dial - no screw removal needed. Now my "anal-retentive" self is satisfied with the results.

This set is "never" used in a machine shop; it's used for metrology, usually in a pretty clean environment. Sometimes, however, another one of the techs will borrow it (for unspecified purposes) and it comes back with, um, 'altered' characteristics. Previously I would just wait until it was time to send it out for recertification, and let the outside lab fix the dial. Now I'm even more valuable to the Company!

I've learned a thing or two since joining this ng 7 or 8 years ago.

Joe

Wow, that was helpful! How much does it cost to "buy" a magic set of calipers?

Fifteen health units. Or two power units.

Duhhhhhh!

LLoyd

Y'all in the metrology lab must be a peaceful and friendly lot. Man, in a machine shop you do not touch another's precision measuring instruments with anything you're not prepared to lose!

On Wed, 21 Mar 2007 08:08:37 -0400, Joe scribed:

Joe:

email me your address to "fred at fvfowler.com" and I'll send you a couple of the pinion tools in the mail.

Best,

Fred

Indeed. Dancing in the parking lot or getting sucker punched would be the least of the consequences.

When you mess with a mans tools..you are messing with his lively hood..and his reputation.

Gunner

"Liberalism is a philosophy of consolation for Western civilization as it commits suicide"

- James Burnham