The spin indexer consists of a face plate and a vernier scale. The face plate is devided into 360 degrees that are represented by 36 evenly spaced holes around the circumference; each hole then represents 10 degress of movement.

I addition there is a vernier scale marked from 0-9 on the top of the indexer body. The vernier scale represents 9 degrees of movement to allow for angular increments less than 10 degrees.

The easiest way to use the indexer is derived by the formula 360 ÃƒÆ’Ã‚Â· (number of divisons required) = (number of holes to move on the indexer). This permits very easy layouts of 2,3,4,6,9,12,18, and 36 divisions. So for example if we want to mill 9 flats on a round bar we devide 360 by 9 and find that the flats need to be milled every 40 degrees.

To do that we take the indexing pin and align both the indexer face plate and the vernier scale to "0" and mill our first flat. (needless to say, on the face plate 360 degrees and 0 degrees are one and the same)

Next we remove the indexing pin from postion "0", and only move the faceplate to 40 degrees and again slip the pin into vernier postion "0" (thereby indexing vernier "0" and faceplate "40") -- we have now moved 40 degrees from our original position and mill our second flat. We simply keep incrementing by 40 degrees to machine all nine flats.

That was easy -- (I hope), but now comes the cool part.

If by chance we need to machine an angle that isn't exactly indexable by 10 degrees -- that's where the vernier scale comes in handy.

Suppose we need to machine a flat at 46 degrees? Well the initial procedure is exactly the same as before; in that we first index at 40 degrees (as outlined previously).

Once 40 degrees in properly indexed, we remove the indexing pin from vernier "0" and slide it into the number "6" position on the vernier scale (40 + 6 = 46) and put some slight pressure on the pin (pushing the pin into the indexing plate)

The pin won't yet slip into a hole on the indexing plate until we slowly move the indexing plate past 40 degrees and the nearest hole in the indexing plate aligns with number "6" on the vernier -- only then will our indexing pin slip effortlessly into that hole and thus achieve a 46 degree angle.

The vernier scale is carefully machined to allow for this slight misalignment and thereby allow any angle less than 10 degrees to be indexed. Obviously, we only need to go to 9 degrees on the vernier because 10 degree intervals are easily indexed on the faceplate itself.

Hope this makes some sense.