Re: [CAD_CAM_EDM_DRO] Re: Tooth belts & gear suppliers

The only thing I can think of is that with stepper systems a large
reduction ratio can mean that the stepper must operate at a high speed
where torque falls off in order to move at high rapid rates. What
those who categorically criticize such ratios often forget is that
they are necessary if one attempts to use motors that are really too
small for the friction losses present in many manual machines. In
such a case, a high reduction ratio will let the machine run reliable,
but with poor rapid performance.

Ie, a 120 oz/in stepper running 4:1 reduction into a 10 tpi screw in
theory produces a huge amount of force, so much so that a lower ratio
would seem desireable. But in practice, I can stall it (even at low
feed rates) by pulling hard on the slide. I believe this is due to
friction losses.

In fact, I believe I have heard that fine pitch sliding-contact (ie,
non-ball) screws transmit no substantially greater force for a given
torque than coarse pitch ones, because of the losses. Such would
suggest making the reduction ratio large for maximum torque to fight
friction, but also putting in a coarser pitch screw to speed rapids.
However, at present I kind of like the fine crossfeed tapering ability
I get with 8000 counts/inch - ie, 200s/r * halfsteping * 4:1 * 10tpi
even if it keeps the rapid rate low. I suppose with the coarse screw
I could buy a microstepping driver for that axis.

Chris

> Mike,
>
> I'm as baffled as you are as to why belts and pulleys are a mistake. I've
> been fortunate enough to visit both Camtronics, Inc and C&G Research and
> witnessed first hand the benefits and wisdom of using belts and pulleys. I
> have also yet to receive any detailed explanation from JanRwl @ AOL.com as
> to the reasons behind their comment that belts and pulleys are a "mistake".
> Seeing how highly regarded Dan at Camtronics and Chuck at C&G Research are
> spoken of here, I'm very curious as to what motivates the comments of JanRw.
>
> Scott
>
> ----- Original Message -----
> From: "Mike Phillips" <mikep_95133@...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Monday, November 05, 2001 7:27 AM
> Subject: [CAD_CAM_EDM_DRO] Re: Tooth belts & gear suppliers
>
>
> > Belts and pulleys are a mistake?
> >
> > Why?
> >
> > Mike
> >
> > --- In CAD_CAM_EDM_DRO@y..., JanRwl@A... wrote:
> > > In a message dated 03-Nov-01 15:51:14 Central Standard Time,
> > > slramsay@n... writes:
> > >
> > >
> > > > I do not want to use a direct drive setup. Instead, I'd like to
> > power the
> > > > ball screws using "tooth belts" and matching gears using an offset
> > axis
> > > > system.
> > > >
> > > >
> > >
> > > Mistake, IMHO!!!!!!!!!!!!!
> > >
> > >
> > > [Non-text portions of this message have been removed]
> >
> >
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-------------------------------------------------
Christopher C. Stratton
Engineer, Instrument Maker, and Horn Player
ccs@... 617 628 1062
http://web.mit.edu/~stratton/www/brassbuild.html