Vernier Caliper Battery Fix

A number of instructables have addressed the abismal battery life of the cheap Chinese vernier calipers, I have one particular caliper that I gave up on some time ago as it went through batteries in even shorter order than most!

I decided it was time to make it usable once more and there were criteria I set myself

• I wanted to make it non fiddly to turn off and on
• it had to be tidy to look at
• it needed to be enclosed to make it rugged

In addition to the vernier caliper the project required the following materials:

• A block of acrylic 23mm W x 70mm L x 13mm thick
• 1mm brass round rod for contacts
• Small on off switch
• spring contact from a scrapped battery holder
• A piece of 1.2mm aluminium sheet 70mm L x 65mm W
• shrink sleeve
• 2 x 3mm csnk screws 6mm L
• 2 part adhesive

The tools used were:

• Soldering iron and solder
• hand chuck with 1mm drill
• 2.5mm drill, M3 dia tap and tap holder
• Hack saw
• Various files
• vise
• Drilling machine/pistol drill
• Milling machine*

* If no milling machine is available the battery holder could be assembled out of 4 pieces of acrylic

I milled a slot in the acrylic block that was around 5mm longer,1mm deeper and wider than the AAA battery.

I cut another slot for the switch and drilled through 8mm diameter to join the 2 slots. This is where the negative contact will pass through.

First job on the vernier was to remove the label on the back which reveals the screws that hold it together. once the screws were removed I was able to drill 2off 1mm holes through the side of the display unit to get the brass rods in to the battery recess and the contacts therein.

I had a negative terminal spring from a battery holder which I chopped up and soldered to the common terminals of the switch, the spring passes through a hole in the battery holder and the switch is attached with 2 self tapping screws . The positive terminal is a piece of brass rod bent to go from the battery compartment of the vernier to the positive end of the AAA battery. I was originally going to make the negative connection with one piece of brass rod but that turned out to be a bit of a faf so it ended up being 2 pieces of brass rod soldered together once the next step is done..

After reassembling the vernier caliper I bent up the aluminium cover and then drilled and tapped the fixing screw holes in the battery holder

I soldered a short stub of brass rod onto the switch contact and another one into the vernier battery holder negative contact.
Using JB weld I stuck the battery holder to the back of the vernier, screwed the cover on and then clamped it lightly in place.

24 hours later with the JB weld fully set I pushed the positive contact into both battery holders and soldered it in place, battery in and flick the switch to make sure it works, it did :)

Finally I fettled the cover to close in both ends to protect the external connections, I used a cyanoacrylate with powder filler to get a good fillet to make the joint stand up to a few knocks .

The modified vernier works faultlessly, yes it is a bit more bulky and a bit heavier but it is once again a useful tool, the power switch falls to hand perfectly as the vernier is picked up and turns the display on without having to touch the vernier power button so on/off is all very easy.

The vernier sits nicely on the bench when put down as the back of the cover is flat.

As usual a poor quality video that shows that it works :)