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

Step 1: Materials and Tools

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

Step 2: The Battery Holder

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.

Step 3: Preparing Power Connections

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.

Step 4: Pos and Neg Battery Connections

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..

Step 5: Aluminium Cover and First Assembly

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.

Step 6: Final Contacts

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 :)

Step 7: Finishing Touches

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 .

Step 8: All Done

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 :)