Sean...I know that I have seen writeups on all the angles and forces involved with a pivoting arm. In fact a lecture I went to about how to set up a pivoting arm is what convinced me to go to linear tracking. It is impossible to get everything right across the recorded range of the LP.
If I had to do it....I would set the tracking angle so that it is correct at the midpoint of the LP recorded range. To accomplish this:
1. Make a template of the plan view (looking down) of the arm. The pickup is mounted at an angle on the arm, or the arm has a bend in it.
2. Put the template on the armboard with the stylus point at the radial distance from the turntable spindle that corresponds to the midpoint of the recorded area.
3. Draw a line tangent to the groove at the point where you located the stylus. This is orthogonal to the radius out to that point.
4. Pivot the template around the stylus point until the arm pivot point lies on the line which you drew.
5. Drill away.
You might want to compare an existing deck (that you know is right) to what my method would yield.
It might theoretically be slightly better to set things up for a point nearer the end of the recorded area, on the basis that things get tough for the pickup towards the inner grooves, and it might help to have tracking angle more optimum at that point. However, I don't think that there would be any significant improvement by doing this.
