# How to calibrate and mark scale on arc segment of a verical drill depth

1. ## How to calibrate and mark scale on arc segment of a verical drill depth

Hello I have a small vertical drill that does not have a vertical depth measure.
I want to measure the amount of vertical movement, and mark this (using a marker for example) amount onto the cylindrical lever center, thus providing a scale on it.
The vertical movement is linear (eg at 1cm drill down, the lever cylinder has moved 12.5 degrees. For 2cm, it has to move 25 degrees and so on).
This is more like a circular-to-linead scale calibration, but the linear scale has to be in metric (because the depth is the interesting part) and it must be presented on the cilynder.

How can I make this scale this the easiest way? Shall I just measure and mark, or there is an easiest mathematical way?

For example, one way I was thinking was to mark the start and the end of the cylinder degrees by placing the drill fully up and then fully down. Then divide these degrees by two, then the two by two etc.

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2. ## Re: How to calibrate and mark scale on arc segment of a verical drill depth

Use basic Arc Geometry to choose a radius for a pointer on the arm such that it points directly in mm. Use a curved tape measure on some mounting plate.

Then add an adjustable stopper to limit travel at the scribed pointer difference in circumference or depth.

You need ;

- a radius so that the scale for circumference is linear with a curved ruler and pointer
- an adjustable datum point for the zero point or object top. (optional)
- an adjustable depth marker or stopper.

For more resolution you can scale the radial pointer to a bigger number.

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