RE: [CAD_CAM_EDM_DRO] Re: I need some feedback on using wire rope for driving...

Sitting here skinning cats and eating crow...

My concern was that as you moved the axis, the feed-point of the cable would
travel up the rod so far as to introduce trigonometric distortion. What once
was the base is now the hypotenuse and you would need a way to let out slack
as needed.

At 8 turns/inch and one inch diameter, to travel four feet, you would only
need to rotate a bit more than fifteen turns or about two inches of travel,
something that could be compensated for with a spring-loaded pulley
follower. Your movement would not be accurate but the distortion would be
linear and the software could compensate for it.

I had it in my brain that we were looking at a foot or so.

Played around a lot with early large-format pen-plotters (knew some people
in companies around Boston when I was living there) and they did cable drive
but it was always a pulley about 8-12" in diameter and only a few turns
wrapped around.

I really hate to think of how many of those machines went into dumpsters
when reliable ink-jet came out...

Dave

> -----Original Message-----
> From: CAD_CAM_EDM_DRO@yahoogroups.com
> [mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of David LeVine
> Sent: Thursday, December 13, 2007 5:16 PM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: Re: [CAD_CAM_EDM_DRO] Re: I need some feedback on
> using wire rope for driving...
>
> Dave Halliday wrote:
> > I am thinking that you would have to go through some
> extreme gyrations to
> > get this to work over more than a foot or two of spindle travel.
> >
> > You can get Acme Threaded rod in large diameters but
> imagine the inertia of
> > a 15" by 2' bar of metal.
> > http://www.keystonethreaded.com/acme.htm
> >
> > I would use thick-wall Schedule 80 PVC pipe with a belt
> reducing system to
> > the motor.
> >
> If you are using something like 1"-8 all thread for the spindle,
> consider making two of them. Let's call them A and B. Cable
> 1 goes from
> A to B, Cable 2 goes back from B to A. A threaded follower
> (think a nut
> with extensions to hold pulleys) goes on each spindle and guides the
> wire rope into the grooves. With the cables parallel to the spindle,
> each turn of A moves its follower to the right a small fraction of an
> inch and moves the follower on B the same distance in the same
> direction. The cables move PI * the spindle effective
> diameter plus or
> minus the pitch per turn, so for a 1"-8 spindle, 3.14159 inches plus
> (or minus) 1/8". No complex mechanism, just two spindles and two
> followers. The followers will ensure that the rope will lay in the
> grooves (threads). Of course tension is maintained and the
> rope has a
> predictable movement.
>
> Just another way to skin the cat.
>
> --
> David G. LeVine
> Nashua, NH 03060
>
>
>
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