Instructions

This Java applet draws the logarithmic spiral used to make Friend-type camming devices. Enter the pressure angle, the maximum size, & hit the "Draw Cam" button. Both numbers can be integers or have decimal parts.

The output is displayed best if 0 < pressure angle < 90 & 0 < size <5. You can try parameters outside these ranges, but the results may be strange. On actual Friends, the pressure angle is about 14.5 degrees, & the maximum size (of one cam) ranges from 0.2" to 5". The smallest cam that would work with the stem shown here has a maximum size of about 0.55", a little bigger than a #1 Friend.

For the curious, the spiral is given parametrically by

x(t) = Rexp(bt)cos(t+ti), y(t) = Rexp(bt)sin(t+ti) ).

Here, R is the minimum size of the cam, b = tan(pressure angle), & ti gives the angle of the initial edge at t = 0.

In polar coordinates (r, t), r = Rexp(bt).

The Close Cam & Open Cam buttons do the obvious things. These applets are computation intensive. They may look (more than) a bit clunky on slower machines.