Re: making an ali flexible coupler

>The rubber spider that's inserted between the two
>coupling halves allows for misalignment.

The spider coupling does not take kindly to mis-alignment. It will
tolerate a small amount of mis-alignment, but will wear out rather quickly
if there is more than an thousandths or two of vertical or horizontal miss
alignment, or more than a few minutes of angular mis-alignment. They can
transfer heavy loads though and do provide an vibration isolation between
shafts. The spider coupling is designed to be a single direction coupling,
so there is a lot of backlash in them. All in all, they are not a good
choice for a CNC coupling.

An easier home made coupling might be patterned off a old (1960s) Ford
steering column to steering box coupling. It was a hub that was attached
to the shaft, and had a very flat U shaped yoke with a flat surface
perpendicular to the shaft. These two halves were attached 90 degrees
apart on a rubber/fiber disk. It allowed for quite a bit of angular miss
alignment as well as some vertical or horizontal miss alignment, and
lasted for many years (unless you were in the mid-west and the floor boards
of your truck cab were rusting out). It also gave a very smooth and
undetectable backlash feel to the steering. I don't have a drawing but
could do a back of a napkin one if you wanted to see it.

Don