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

>
> On 12 Apr 00 at 0:36, CAD_CAM_EDM_DRO@egroups.com scribbled
> furtively:
>

Sorry, it just doesn't fly, airfoil comparisons elsewhere not-
withstanding.

The problem probably comes from logic similar to airfoil theory,
fluids and relative movement due to differential pressures.

It doesn't apply here.

> because the tape is attached to the table and must move at the same
> speed, and when you deflect the tape with the wheel it now
> travels around a radius,

True.

> and that circumferential distance is
> larger than the straight line distance,

True.

> the tape must travel around
> the radius faster in order to maintain it's length since the tape is
> not stretchy (to that degree anyway).

Nope. Not True.

The length of the Tape/Wire/Cord/Shim stock is already of a length
to allow for the extra bends it has in it.

Please Excuse the ugly ascii art.

C
/0\
0/ \0
J ------------------ --------------------------- K
A B

The presumption above is:
The "Wire" must move from A to C to B in the same 'time' it would
have taken it at a constant speed to travel from A to B.

This in simply not true.

As a whole the wire will move the same distance over whatever path
it set up tp follow.

Ignore the flexing of the wire for the time being.
Say the wire moves right 1 Inch.
All points on the wire from J to A and from B to K will move right
1 inch.
All points from A to C to B will still move 1 inch.
It may be up, down or around an arc, but it will still move only
one inch.


The "Stretchy" issue you mentioned is actually quite the opposite of
what you presume above.

IF points A & B were Pinch rollers that were geared to the movement,
such that they fed out and took up the "Wire" at a constant speed
identical to the movement of the wire or head.
AND the wire was originaly the length of the distance from A to B.
AND it was stretchy enough to then pull it around pully C, then it
would work as you propose.

Even if it was that stretchy, without the pinch rollers, the "Wire"
as a whole would stretch to the new length over its entire length,
and would act as described above for the first example.


Marc