Fix your stupid cheap digital caliper

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.

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?

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.
.

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.

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.

Yes CI, easily the most used item and therefore really annoying when it plays up!!

Chris, we always used to put a dab of 'Vaseline' petroleum jelly on car battery contacts to keep moisture out - I rarely even look under the bonnet (hood) of my car these days, there's nothing to see except black plastic.

Steve, thankfully my garage workshop is very dry but it does get pretty cold. I've got a bunch of unused, sealed, erasers I use for archaeological drawing but they're labelled 'PVC and Latex Free' - I wonder what they're actually made from, some other sort of plastics??. Presumably they also contain an abrasive compound.

Does depend on the calliper, mine switches completely off and does not remember last position and a battery will last 2-3 years quite easily.

I'm still on the same one my brother gave me back in the early 80s when he no longer had the need for it. So probably quite cheap in the long run when compared to getting through several cheap ones and a continuous supply of batteries. It is a Mitutoyo. Not had problems with it.

Well that seems to have worked! Using a magnifier I could see some greyish build up on the high point of the battery contact (and a small blister in the chrome plating lower down but not in the contact zone). I cut up a used eraser to get some unused surfaces and gave the contact a good rub. It's now nice and shiny, the readings aren't all over the place and even the buttons seem to be working with just a light touch rather than having to hold them down as I did before. Before and after photos. A bit of the grey stuff is left on top of the eraser in the second photo but I broke that corner off while being a bit over zealous!

Jason, yes, I think I had one of those types a while back. Paul, great, glad it worked. 

Guys, yes vaseline and bearing grease works great for those kinds of big contact surfaces and 12 volts. When you get down to micro components and contacts at 2 volts it's probably kinda thick for them. I was trying to find a video I saw years ago about Corrosion X when I was making R/C models. I just found it. This stuff is pretty different from a grease. In model aircraft back then, we used fairly hazardous LiPo cells and ESC speed controllers which DID NOT like water (Chris I'm sure with subs you know). Not to mention the receivers and servos...

This video shows Corrosion X being tested in this kind of ...ahem.... "damp" environment.



I've used it to save other kinds of dunked electronics after they got wet, and also on connections to things like depth sounders on my boat.

Steve, the electronics in the subs definitely don't like water! We use ESC's that are waterproof in case of leaks, waterproof servos are easy to come by, the receivers not so much so we mount them up high in the watertight compartment, and if things do get flooded bad (like bottom of the pond and swimming to recover bad) then its real important to get the case opened up and dried out quickly. Normally its not a problem at all unless a seal fails on the through-hull fittings. We only run in fresh water, salt water disrupts the radio signals too much, so at least no salt corrosion issues.

Ah, Chris, I'm behind the times on what's available these days in R/C. I think when I got my small spray can of Corrosion X (red label) it was ten bucks -- which I thought was a lot. But it has saved many times that amount of wet electronic equipment since then, so I'm glad I still have it. Probably still half a can left. I might try it on my digital calipers. My shop floor is now covered in melt water from the snow banks all around. We still have a foot on the ground everywhere, and with frost heaves the concrete shop floor is now lower than the surrounding snow. Hope is on the way though. I saw a robin today!

Quote from: vtsteamAh, Chris, I'm behind the times on what's available these days in R/C. I think when I got my small spray can of Corrosion X (red label) it was ten bucks -- which I thought was a lot. But it has saved many times that amount of wet electronic equipment since then, so I'm glad I still have it. Probably still half a can left. I might try it on my digital calipers. My shop floor is now covered in melt water from the snow banks all around. We still have a foot on the ground everywhere, and with frost heaves the concrete shop floor is now lower than the surrounding snow. Hope is on the way though. I saw a robin today!

The snow is pretty well gone here, melted off the last couple days! There was this big bright yellow thing up in the sky too that I haven't seen in a while, and the clouds were all blue...

Sounds nice -- being east of you we get our weather second hand after you guys are through with it, so I'm hopeful after the sound of that! 

In cheap stupid digital caliper quirks news, I just received another one today from the big river company, and guess what? Out of the box it reads exactly half of what it should. 

This one has an actually good new feature -- the battery compartment cover has a single screw to hold it down instead of being a maddeningly difficult sliding hatch. The sliding hatch style also is a poor design for pressing the battery down against its spring contact. The screwed cover is gosh, a better idea.

I even received a screwdriver with the caliper to remove said cover. Which I did so I could remove the battery by way of forcing a reset to the electronics, since I don't have as much use for a half reading as a full one.

Luckily for all involved in my transaction to purchase said caliper, that restored it to sanity, and an inch measures an inch now, not to mention also that a mm now measures a mm.

So here is tip number two in fixing your stupid cheap digital caliper if it reads half of what it should. Take the battery out and put it in again.

Sounds like dealing with computers! Power cycle, reseat plugs, reload Windows, throw it out the window...