Re: [CAD_CAM_EDM_DRO] Rotary to linear translation - an interesting idea.

"D.F.S." wrote:

>

> Because the Length of that compressed surface will not be the same
> as the Length of the centerline on the ribbon or cable.
>
> To restate your statement:
> The wheel interfaces with the surface of the ribbon, which is
> compressed. Not it's centerline which is the length we are
> actually trying to measure.

Ok, I think I see your logic here. Well, I'm math challenged, but CAD
capable. I drew a 1" dia circle and a .998 dia circle. Trimed to a 60
degree arc for both circles. I assumed a .005 ribbon. When metal bends,
it stretches more than it compresses and the theoretical centerline does
not follow the exact center of the material through the bend, that's why
I went for .002 difference instead of .0025. Across this arc, the 1"
segment was .523599 and the .998" segment was .522552 long, for a
difference of .001. We'll forget about the 47 millionths as that's
beyond the scope of hobby level machining.
So we do see a change to the distance of the ribbon where it wraps
around the wheel. However, I think we need to take into account the fact
that there are two bends in the opposite direction which will be
-stretching- the same surface we are trying to measure against. Since
the material stretches more than it shrinks in a bend, one would have to
really pay attention to these effects to make sure they don't cancel out
the very compensation they are trying to effect.
I can't quite explain why, but I still don't think it's real-world
workable. Maybe I'm too hung up on the Travdial model of operation.
However, I'll admit it's possible in theory, and would really like to
see someone make a working example and prove it in practice before I
fire up the BBQ...<G>

Jon