Ruler calipers

These sliding arms allow you to transform a ruler into a large vernier caliper. Useful to measure very large objects that are too big for a normal caliper, as long as you don't need great precision. The arms are 120mm long (4 ¾") which means you can measure round objects up to about 240mm (9 ½"). One of the pieces has a 20mm deep hole on one side only, and this will determine your zero point; just subtract the leftmost value showing on the ruler from your final measurement.

The model was designed to fit a cork-backed Staedler metal ruler, as pictured. If you want to use it with a different ruler, you will need to measure its width and thickness — using normal calipers! — and scale the model accordingly, making sure to leave a tolerance of 0.4mm (so the arms slide comfortably but don't wiggle too much). For reference, the Staedler ruler has a width of 25.5mm and a thickness of 1.8mm. I included a test piece that can be used in case you want to try scaling the model. If the ruler's dimensions are too different, scaling may be a problem, so you can always drop me a comment and I can create a custom version.

I suggest setting your slicer to print outer perimeters first so the slot will be as straight as possible.