Re: [CAD_CAM_EDM_DRO] Re: DRO encoders- Rotary or Linear?

This may be a stupid question, but why not to use a normal bicycle
chain\sprocket combination for driving an encoder?
Is it a backlash issue?
Alex

----- Original Message -----
From: jcc3inc <jccinc@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, October 29, 2002 9:44 AM
Subject: [CAD_CAM_EDM_DRO] Re: DRO encoders- Rotary or Linear?


> --- In CAD_CAM_EDM_DRO@y..., "Roger Linscheid" <r.linscheid@a...>
> wrote:
> > Hi, I am ready to begin adding a DRO to my G4003 lathe. What is
> the
> > current thought on the best method to accomplish my goal?
> >
> > IIRC, when I was looking into this before, the linear strips from
> > U.S. Digital were only available in 250 CPI and this was not
> > considered high enough to provide the necessary resolution. Using
> > rotary encoders meant the possibility of losing counts if the drive
> > cable slipped or stretched.
> >
> > Now U.S. Digital has linear strips in 300 and 360 CPI. Will these
> > provide a resolution of 0.0005 or better?
> >
> Roger:
> Since you seem interested in accuracy, why not use rack and pinion
> for rotary encoder drive. A 1/10 inch circular pitch rack with a 20
> tooth pinion requires a 500 count encoder to read .001". Precision
> rack is available from PIC Instruments, Berg, and Allied Devices.
> They can also provide you the pinions. Less expensive rack is
> available elsewhere.
>
> Linear encoders eliminate backlash and encoder mounting errors and
> are probably the better of the two approaches. A 250 line scale will
> give you (with 4x multiplication) a .001" resolution. A 360 line
> scale yields 1440 steps per inch or .6944 mils per step.
>
> Good luck,
> Jack C.
>
>
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