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
- 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 :)