Can dial calipers be fixes when the readings start jumping around?

I have had a set of $20 calipers from China for 10 years that have worked very well, repeatability of .0002" if I do my part.
Now the readings are jumping back and forth, some right on the money, some ~.004" off.
Should I toss them, or is there some way to get that dial off and clean those spur gears in there?
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Yes, dial calipers can be disassembled, although the dial mechanism may not be the problem.. instead, there could be dirt/debris in the rack and pinion gear located behind the dial mechanism/gear box.
Another part to check would be the slide lock, which holds the slide properly aligned on the bar. Some have tiny setscrews that can be adjusted to eliminate any slop in the fitting of the slide. Errors are introduced when/if the jaws aren't nearly perfectly parallel.
With the caliper in the full open position, some solvent and a small brush can be used to clean the exposed rack (a good magnifier lamp is helpful), and with a little fiddling, a drop of solvent can be applied to the small pinion gear that meshes with the rack. Some duster/canned propellant can be used to blow out excess solvent and likely, the dirt with it.
Opening the actual dial mechanism may be fairly easy, or possibly somewhat difficult if one isn't familiar with small mechanisms. A puller may be needed for pulling the pointer off, but maybe not.. they can often be persuaded to come off with some gentle manipulation.
Under the dial face is where the small gears are, and a tensioning spring to eliminate backlash. It's less likely that dirt or foreign objects have entered the gear case, but maybe something has gotten in there. It's best if the slide stays slightly tensioned, so the back pinion gear doesn't skip and need resetting, which can be a little troublesome if required.
--
WB
.........


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snipped-for-privacy@gmail.com wrote:

Your mileage may vary...
I've had a Browne & Sharp caliper for years and it started getting all jumpy and gritty, probably from chips in the rack. After considering the cost of a new one and that there was little to lose, I flooded the rack and the area under the dial with LP2 and then blew it out with an air hose.
It's now accurate and smooth again.
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wrote:

Keep your thumb over the plastic lens whenever using compressed air or you'll end up blowing it off.
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Sorry dude
.but once a cheap caliper goes south..get a new pair
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On 3/28/2011 6:38 PM, snipped-for-privacy@gmail.com wrote:

On the other hand, quality calipers can take a licking and keep on ticking. I did a few small lot jobs for a larger shop some years back. Owner was sawing me out a few blanks, and while measuring the first one, complained about something in the rack of a well used B&S 6" dial caliper, and hucks it 20' into a trash bin. I asked if I could have it. He looks at me funny but says sure. Took it home, disassembled and cleaned, put back together. It sure doesn't feel good at all, but is within a thou or two across the range. Wouldn't use it for any machined work, but I keep it around the saw for checking cut lengths.
Jon
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On Tue, 29 Mar 2011 09:19:38 -0800, Jon Anderson

Gee, I didn't know Briggs & Stratton even made dial calipers. ;^)
-- Most people assume the fights are going to be the right versus the left, but it always is the reasonable versus the jerks. -- Jimmy Wales
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snipped-for-privacy@gmail.com wrote:

Speaking of Chinese no-name calipers, I have one that I let some klutz borrow once, and when I got it back, at 0.000, the needle points at about what was originally about 0.025. Joe the real machinist showed me the setscrews, said to loosen them to disengage the rack from the pinion, and just re-zero the needle.
For some reason, I'm afraid. (I finally found my jeweler's screwdriver.) I guess what I'm afraid of is, how much should I loosen the setscrews?
I know I can simply count turns of the setscrews and then just retighten them after the "adjustment", but I guess I'm wondering - how much to loosen them to really disengage the rack from the pinion without it falling apart?
Thanks, Rich
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On 3/28/2011 7:24 PM, Rich Grise wrote:

Might not get enough slack to disengage the pinion. This is easier: Slide the movable jaw HARD and FAST into the fixed jaw. The sudden stop will cause the needle to move. It might take several revolutions to get it to line back up properly.
OK, just kidding, that's an early April Fools joke...
Look at the back of the dial, at the top, and see if there isn't a shallow groove perpendicular to the beam. If so, this goes straight down to the pinion. Most calipers come with a little rectangular wire that is inserted into this slot to gently disengage the pinion. Simply position the needle at zero, depress the pinion, slide the jaws together, and release the pinion.
Jon
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Jon Anderson wrote:

Thanks, but no groove. But I did notice there's somewhere between 1/16" to 1/8" of daylight between the beam and the top of the slider, so it's not likely to fall off, and I should know when to stop unscrewing by watching that gap.. ;-)
Thanks!
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~ 8 years ago I bought a Fowler Sylvac 6 digital caliper because I needed both metric & imperial unit w/o making conversion calculations. Other wise I would have bought a dial caliper. From the get go, I would turn it on & slide it down the rail & back to zero, it would usually show a negative mil. Or half a mill or a hundredth of a MM. After re zeroing & sliding it down again usually it would read zero. But not always. Sometimes it would read plus a unit. Eventually it would settle down. But if I let it sit turned on for say 20 minutes occasionally it still would not zero. Recently it seems to have gotten worse. Being the 1st electronic precision instrument I have ever used, I thought this might be normal. Now I'm beginning to wonder. Is this normal or not? Your thoughts? Thanks, JD
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wrote:

~ 8 years ago I bought a Fowler Sylvac 6 digital caliper because I needed both metric & imperial unit w/o making conversion calculations. Other wise I would have bought a dial caliper. From the get go, I would turn it on & slide it down the rail & back to zero, it would usually show a negative mil. Or half a mill or a hundredth of a MM. After re zeroing & sliding it down again usually it would read zero. But not always. Sometimes it would read plus a unit. Eventually it would settle down. But if I let it sit turned on for say 20 minutes occasionally it still would not zero. Recently it seems to have gotten worse. Being the 1st electronic precision instrument I have ever used, I thought this might be normal. Now I'm beginning to wonder. Is this normal or not? Your thoughts? Thanks, JD
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I have an $8.00 Chinese digital caliper that does not do that. Only problem is it appears to use up batteries even when not turned on.
Is there a raised ding on the edge of your jaws, or perhaps your slide is too wobbly?
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Asshole.
You owe me a beer.
And a keyboard.

A sheet of thin brass thats been sheared to about .050 wide can be adapted to do the above also--roll the gear up onto it by one tooth, move both brass and reader head over by a tad bit and then slide the brass shim back out.
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