Re: [CAD_CAM_EDM_DRO] Updated DRO using screw threads not pulleys

An old plotter that I had used a drum and coated wire to move the pens. the
wire was fixed at the center of the drum and when the pen was at one limit,
one half of the drum was full and the other half was almost empty. That way
the wire always traveled in the same place on the drum.
Darrell

----- Original Message -----
From: "dave engvall" <dengvall@...>
To: <CAD_CAM_EDM_DRO@egroups.com>
Sent: Thursday, August 17, 2000 7:35 PM
Subject: Re: [CAD_CAM_EDM_DRO] Updated DRO using screw threads not pulleys


> Doug Fortune wrote:
>
> > Ian Wright wrote Fri, 7 Jul 2000:
> >
> > > I have been considering a similar set up to yours for a DRO but I was
going
> > > to use another pulley outboard of the encoder as well. By doing this
you can
> > > take a complete turn around the encoder shaft (yes, I know it will
screw but
> > > I thought that the shaft would probably be polished enough for the
line to
> > > maintain a reasonable position) and it also takes all the strain off
the
> > > encoder shaft.
> >
> > How about this improvement? What we'd like is to do is wrap the wire
> > several times around the encoder shaft to:
> > - increase holding friction (so the wire doesn't slip)
> > - take bending strain off the shaft (so the encoder shaft is in the
middle,
> > not the end), and say the wire comes from left, around the shaft a
few times,
> > and unspools right.
> >
> > We can't do this with a bare shaft, because the wire wants to 'walk'
down
> > the shaft and wear by rubbing against itself. Also presumably there
are pulleys
> > at the ends which don't walk, causing misalignments.
> >
> > Answer:
> >
> > Instead of using pulleys and bare encoder shafts, substitute screw
threads
> > everywhere. The wire sits in the grooves of the screw threads.
> >
> > In the center is an encoder shaft with screw threads, so the wire
> > (for encoder or even direct power drive) winds around the screw threads
numerous
> > times, and also at the ends, the wire "walks" down the screw threads at
the
> > same rate! Everything stays in alignment.
> >
> > Doug Fortune
>
> This was pretty standard technology for early x-y plotters, plotters for
IR spectrophotometers. There should still be a lot of this
> old technology around to scrounge parts off of. Look for names like
Beckman, Perkin-Elmer. etc. Actually they were drums of
> reasonable size at each end with one end connected to the servo, comb on
the spectorphotometer( for null, etc ). If I remember
> correctly they took about three turns (arond the drum) of stainless steel
wire or teflon-coated SS wire....check sporting goods
> for teflon coated stainless steel leader.
>
> Dave
>
> >
> >
> >
> >
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> >
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>
>
>
> Welcome to CAD_CAM_EDM_DRO@...,an unmoderated list for the
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>
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