Dial caliper

A friend has a Chinese made dial caliper that he dropped and now when closed and the O at the top it reads .015. He can loosen the screw that holds the dial and rotate it to zero but
he'd like to have it zero out at the top. I don't think the rack can be moved that much. How can he reset it?
Engineman
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engineman wrote:

What does it matter where the ZERO is? ...lew...
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    Convenience in reading, mostly.
    Enjoy,         DoN.
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It doesn't really matter WHERE 0 is, just that it can be zeroed, and more to the point, the tips aren't bent after being dropped. Some of the better imports had a narrow shim supplied in the box that could be used to move the pointer, the pinions on those are spring loaded so just wedging them out of mesh with the rack would move the pointer. Not sure if they're all built that way, but it works for those. The shim is a couple of thousandths thick or so and narrow enough to fit in the rack groove. I've also seen some where the back of the slider was held on with some fine screws, pulling those will let the slider come off forwards, reassembly will be up to you! If you're lucky, you won't need watchmaking tweezers to reassemble.
Stan
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Your friend's preference is reasonable to me. I prefer to have 0 stop at the top, it just seems much easier to read more quickly. Reading a clock wouldn't be as easy (at a glance) if a different number was placed at the top.
After a friend borrowed a dial caliper, it didn't read zero at the top, but it turned out to be a slight burr at the tip of one of the jaws, from rough handling, possibly where it hit if it was dropped.
If the bezel can be removed, the easiest way would probably be to gently pull the pointer off and reset it at zero.
I did a reset the hard way a number of years ago, and can't remember the details now, but it took more than a few tries. I think I removed the stop at the end, and ran the entire dial assembly off the scale, then put it back on to see where the pointer stopped when closed. I think I eventually removed the screws from the rack, and moved the rack to get the desired position. If I hadn't approached it as a challenge, it wouldn't have been worth the trouble.
It still works fine now, but I use a digital more frequently.
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Wild_Bill wrote:

How in the world did you get the "anti-backlash" spring loaded gears back in correctly. That was the problem I had with the one from school I tried to fix. It's still setting on my desk a few years later. :-) ...lew...
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Lewis Hartswick wrote:

I've never seen a dial caliper with an anti-backlash spring. I have seen that in 1" dial indicators, and you can wind up the spring from the back of the indicator before reinstalling the plunger.
If some calipers have springs, I'd guess it would only be the more expensive Fowler, Mitutoyo, Brown & Sharpe, etc., not the Chinese ones.
Jon
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I don't remember if the cheap model from China had anti-backlash, or not. I had experience working with small mechanical assemblies, so the challenge didn't seem impossible, but since I hadn't taken a dial caliper apart before, I didn't know what I was doing.
Take an old dial indicator apart, and if that goes well, try fixing the caliper. If it's an expensive caliper, maybe send it out for repair.
Long Island Indicator Repair has been recommended here in RCM in the past, for repair parts.. their repair flat rate for a 6" is $65, up to $125 for a 12" model.
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Wild_Bill wrote:

Without the correct tool, a Jeweler's watch hand puller, you can break the end off the pinion. I wouldn't even try this on a Chinese caliper.
Jon
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Some dial calipers, Mitutoyo in particular, have a thin groove running down the back of the dial housing, perpendicular to the rack. They come with a rectangular wire that you slide down this groove, which pushes the pinion away from the rack. You set the pointer to 12 o'clock, insert the wire, then slide the jaws closed. But this only works in .025 increments on any caliper I've seen.
For others, I have some fine tipped curved tweezers. I remove the crystal/bezel, which can be frustrating on some imports, then gently pop the needle off the shaft, being careful to lift only under the needle's hub and not on the needle itself. Can take a surprising amount of force, but I've never damaged anything doing this. Make sure the jaws are clean, close them, and press the pinter back on at 12. Not a big deal really.
Jon
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engineman wrote:

I had that problem with my Chinese caliper . I loosened the gib screws on top enough that the pinion was disengaged from the rack and re-adjusted it by trial and error . Not that it did much good , that caliper lives on the lathe and/or mill , and it has a habit of attractin' swarf . That's why I got digitals ...
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I'd just tell him to get over it and move the bezel. I'll bet it takes a little fooling around to get the needle exactly back to "12 o'clock" if you do it that way. Chances are good that he'll drop it again, or that a piece of crud will get on the rack at some time, causing another move from zero.
Pete Stanaiits ----------------
engineman wrote:

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On Mon, 1 Feb 2010 13:04:21 -0800 (PST), the infamous engineman

There are small copper reset keys for most calipers, E. One of the guys here sent a couple to me the last time my dial went wonky.
-- Imagination is the beginning of creation. You imagine what you desire, you will what you imagine and at last you create what you will. -- George Bernard Shaw
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engineman wrote:

Did a little bent piece of brass shim stock come with the caliper? If not, you can make up such a thing. You open it up to the maximum width, and then the tiny pinion gear is near the tail of the beam. You can work the thin sliver of shim under the pinion, and make it skip a couple rack teeth as you move the jaw. When you get it skipped the right number of teeth over the rack, it will reset the pointer to point where you want it to.
It is sometimes easier to do this when you remove the stop on the end of the beam that prevents the slide from coming off.
Jon
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    I don't think so either.
    However, what probably happened is that the pinion gear bounced out of mesh with the rack, and skipped one tooth before re-engaging.
    There *may* have been a tool for fixing that problem (which occurs from time to time -- sometimes because of chips getting into the rack). It would be tucked into a slot in the foam lining in the box in which it lives.
    It is a thin flat spring with a wider grip surface which can be worked into where they mesh to disengage them and skip them to a new mesh point. It may take a few tries to reach the correct point.
    *Or* -- you could remove the screws holding the carriage together, disengage the pinion and reassemble -- trying a few times until it lines up again.

    Two suggestions above. Both require a fairly delicate touch, and the latter a workplace which makes it easy to capture the screws and such -- something like a cafeteria tray.
    And -- this can happen with other brands as well -- even Starrett.
    Good luck,         DoN.
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