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Fix your stupid cheap digital caliper

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vtsteam:
I started out with a cheap dial caliper twenty six years ago and it got me many years into hobby machining without complaint. Then, digital calipers came in, cheap enough for me to afford, and well let's be honest, longevity wasn't their strong point, but maybe I'd get a couple years out of them, seemed like. I still liked my dial caliper but it had suffered in many ways, particularly fine swarf occasionally getting into the rack, a crystal got cracked, etc.

Well back to the present, one more el cheapo digital purchased from Ebay. But this time it hardly lasted a month before it started going crazy. Zero resetting, mm going to inches and back again, numbers flashing. It was impossible. So maybe it was time for a new battery.

But nope, it seemed to fix it for about ten minutes, and than back to flakiness. So, final resort, take the battery out and examine the little spring contact -- these can get bent down, and a gently pry upwards with say a toothpick can sometimes restore things. Put it back together, and......nope. Same problem.

Okay final effort before tossing in the garbage can. I took a pencil and lightly polished the contact with the eraser -- rubbing it back and forth over the top about twenty times. Reassemble. It worked. No more glitches. stable display. I racked the caliper back and forth fast as I could for a couple minutes, then back to closed. Display said zero, so great. Done.

I've seen a lot of complaints on Amazon reviews about these kinds of calipers, and people describing  the same symptoms. The contacts in these things are easily bent downwards, and even a minute amount of invisible oxidation on that contact surface can reduce operating voltage and increase noise to the point they are unusable for measurement. In many case the fix is easy per above. Maybe most everybody here already knows about this, but just thought if anyone doesn't, I'd mention it.

BTW yup, better calipers of major precision brand are better all around, and yup I do like dial calipers better, and yup, I even got myself a new one after this cheapo digital went awry.

But also fixing this one was worthwhile compared to tossing it out. It's now a spare, and sometimes I like a double check on a measurement just make sure my aging brain hasn't misread one or another form of display. It has more than once.

PaulR:
Very timely Steve, my cheapo digital has been playing up so I changed the battery and lifted the contact a little three days ago but it's still random - often if will come on showing zero when closed then the number will increase as I open it then it will go back to zero as I clamp it on the thing I'm trying to measure. It also randomly turns off but will come back on when it fancies!! I'm going to try your eraser trick see if that fixes it. Mind you I've had this pack of button batteries for a few years and not sure if they have a limited lifespan?

CI:
I bought several digital calipers a few years ago when they were on sale (brand-x generic).
The battery contacts are a bit sensitive.
I intend to convert one or more to operate off of a standard AAA alkaline battery.
I have tried this in a temporary connection, and it worked well.

I use digital calipers as a poor-man's DRO.
I mainly use one clamped to the lathe carriage, and it works really well.
When I get time, I will add one to the mill vertical axis also.

I just clamp the caliper on without modification, so it is easy enough to replace one, or remove it and use it in a normal fashion.
I think digital calipers are the most used item in my shop.
Second most used item I think is the micrometers, which have the mechanical wheels in them to give a digital readout.

Digital readout is the best thing that has ever happened to the machining hobby, in my opionion.
I would not more go back to a manual micrometer or dial caliper than I would go back to a slide rule; no reason to use manual stuff.
I think in digital.
.

vtsteam:
Paul, a pencil eraser has a small amount of fine abrasive material in the rubber. Works great for some kinds of contacts as long as it's a good or new eraser.

When they get old, not so good, just like on paper. In fact try it on paper first if it's an older pencil. If it leaves a black smudge instead of erasing cleanly, find another one.

One of the causes of oxidation on these tiny battery contacts is humidity and condensation in the shop plus the small amount of electric current always flowing in a caliper through the gap between battery and contact. It's a form of electrolysis. In a dry heated shop much less likely to happen.

Why continuous flow? Because when a caliper is "turned off" it isn't actually. Just the display is turned off. A small current is required to maintain its position in memory. So it's really always on despite the on/off button. This also explains why they will use up batteries even if you haven't used it in a very long time.

I was thinking today that I ought to try putting a tiny amount of "Corrosion X" on the contact of mine to prevent future oxidation problems.

That's another tip I have. That product (if available where you are) is amazing for electronics in general for preventing corrosion. It's not cheap, but a can has lasted me ten years. I used to use it on R/C seaplane receivers and connections, and it truly would allow those to work after they got wet.

crueby:
On trailer lights for the boat, we used to put a dab of the trailer wheel bearing grease on the contacts, it would conduct and also keep the air and moisture out.

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