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