The vernier caliper: a new lease of life for defective electronic calipers

Converting a broken electronic caliper to a vernier caliper

A few years back I bought a cheap caliper of the Aldi "Workzone" brand. This particular unit consumed batteries faster than I consume chocolate, and one day I found that the unit was dead: a drained battery had leaked and destroyed the electronics beyond repair.

However, the mechanical construction of these calipers is quite solid, so I converted my broken caliper into a unit that does no longer need batteries: Just like in the good old times, the sub-mm scale is read with a vernier scale (in German: "Nonius").

Materials

• 1 defective caliper
• 1 sheet of glossy white paper, or 1 transparent sheet for overhead slides 
• 1 b/w laser or inkjet printer that can print on the aforementioned sheet without melting it
• Your preferred 3D printer and filament

Preparation

1. Remove the broken electronics from the caliper: peel off the label on the back, unscrew all screws, remove the cover and continue removing screws until the unit falls apart ;-)
2. Print the frame. The material does not matter (as long as it is solid 🤣)
   • Print face down, as shown in the images.
   • The thumb wheel needs support material - again, see images.
   • The layer height determines the smoothness of the display "window", so you may want to use 0.2 mm or less.
3. Clean the print by removing the support material. 

Printing the Vernier scale

1. Using a conventional 2D printer 😋, print the file “vernier-40mm.pdf”. You should obtain a grid pattern.
   • Important: Print without any scaling. 
2. Verify that the distance between the first and the third thick grid line is exactly 39 mm. 
   • If this is not the case, something is wrong with your printer or your computer (printer scaling?) and you may want to get help.
3. Cut a strip that is about 2.5...3 mm wide and about 43 mm long (i.e. there are exactly 10 lines). This is your new vernier scale.

Note: I printed this on a transparent sheet since I had planned to mount the vernier scale across the entire window of the frame. However, I actually prefer to have the scale right on the edge of the display → if you do not need the transparency, simply print on a sheet of (preferably glossy) paper. 

Assembly

1. Slide the thumb wheel into the frame. The wheel must spin freely. 
   • If it does not spin freely, take extra care to remove all the residues of the support material.
2. Slide the new housing over the caliper, starting with the thumb wheel.
3. Optional: Glue the frame to the caliper. I did not do this since the frame does not move (on my caliper).
4. Set caliper to zero (leftmost) position.
5. Align the strip with the vernier scale onto the lower, inner edge of the caliper "window" as shown in the photo below.
   • The leftmost mark is exactly on the zero mark of the caliper. 
   • The 10th mark will automatically align on the 39-mm mark of the caliper scale.
6. Carefully glue the strip in place, without changing its position.
7. Done. 

Enjoy :-)

Edit 2022-12-11: Added the FreeCAD source file, same license CC-BY-SA.