RE: [CAD_CAM_EDM_DRO] Re: home switches

Hi,

Ballendo is absolutely correct as to accuracy.
The SS Plunger type with a roller on top are rated at .01mm repeatability.

These are standard brands Square D, Allen Bradley, etc. Automationdirect.com
brand labels the Telemechanic brand and sells them for $34.00 US each. Check
out the ABM models.


Best,

Ed Gilbert

Gilbert Engineered Systems
632 Warrenton-Embro Road
Macon, NC 27551
252-257-0539

> -----Original Message-----
> From: ballendo [mailto:ballendo@...]
> Sent: Tuesday, March 23, 2004 9:54 PM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: [CAD_CAM_EDM_DRO] Re: home switches
>
> Hello,
>
> If you do a search of the archive for home switch, you'll find
> perhaps a hundred posts... (25 by me<G>)
>
> The short answer is: Microswitches of the proper type--and even some
> relative cheapies-- are far more repeatable than is often imagined.
>
> Second, if you AND a single slot index wheel with your microswitch,
> and use an optointerrupter for reading the index wheel slot, you can
> get even better repeatability. This is the standard technique used in
> commercial cnc machines; where they just use the existing servo
> encoder's index pulse AND'd with a mechanical switch.
>
> Hope this helps,
>
> Ballendo
>
> P.S. Try the microswitch by itself first. Less work, and you may be
> quite surprised. Putting the surprise odds in your favor is a good
> homing routine. Slam into the NC switch, reverse, slow WAY down, and
> move OFF the switch to find home. Since you're moving at a slow rate,
> and that rate is the same each time, repeatability is pretty decent.
> You are also in a state that a wrong move will RE-trigger the switch.
> An important consideration often left out...
>
> If you choose an oiltight submini simulated roller, it is low cost
> and can handle at leat some of the rigors of the machining
> environment. Certainly okay for your micromill, IMO.
>
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "david_margrave"
> <david_margrave@y...> wrote:
> >
> > Hi
> >
> > I'm a bit confused about the whole concept of home switches. How do
> > you get any degree of accuracy and repeatablity based on mechanical
> > contact of a switch closing? What sort of things have people done
> > for this? Just wondering because I'm at the stage in my micro mill
> > CNC project where all I have remaining is wiring up the
> > home/limit/stop switches. The stop switch was easy - just connected
> > the switch to the output-enable pins of the allegro-micro 5804
> (maybe
> > some pull-up resistors were used to, I forget exactly). I am using
> > EMC on linux.
> >
> > cnc project page http://www.margrave.com/static/cnc/
> >
> > Dave
>
>
>
>
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