I needed a small but precise rotary table to cut discs and do light radial milling on my mini drill stand. I decided that an accuracy of 0.1 degree was enough, but it obviously called for some form of Vernier measure. This seemed daunting at first, but after playing around a bit with Coreldraw it turned out to be surprisingly simple!
If you have read this far, you probably don't need a tutorial on verniers, but for the curious here is a short review:
Verniers allow the user to make precise fractional measurements of distance.
To do this you need a ruler with two scales. One scale is moveable and marked in the ordinary manner in millimetres, inches or degrees or whatever you fancy. The other ruler is fixed and graduated in a special way, depending on the resolution required.
We'll decide on a linear scale with 0.1mm resolution.
Therefore, as in the first picture, our moveable scale (blue) is graduated in the usual millimetres. (I only work in metric).
If you look closer at the yellow (fixed) scale you'll notice that it also has 10 divisions but spans only 9mm. It follows then that each of the fixed divisions is only 0.9mm in length which in turn means that the difference in length between the fixed and moveable divisions is exactly 0.1mm, which is our required resolution.
Therefore: to get the first divisions in line the moving scale has to travel to the left 0.1mm,
to get the second divisions in line the moving scale has to travel to the left 0.2mm,
to get the third divisions in line the moving scale has to travel to the left 0.3mm,
and so on.
Doing all this in only 10mm of space makes things a bit crowded so we'll expand the fixed scale in 1 + .9 = 1.9 mm increments as in the following picture.
That makes reading the Vernier a lot easier, as in the following images showing 0.1mm, 0.3mm and 20.5mm excursions.
Now that you know how a Vernier works, you can make your own.
All you need is a printer.
This time we'll do a circular scale in degrees with an 0.1 degree resolution, in other words a protractor.