RE: [CAD_CAM_EDM_DRO] Sensor for home in CNC machine

-----Original Message-----
From: Roy J. Tellason [mailto:rtellason@...]
Sent: 12 February 2004 03:07
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Sensor for home in CNC machine

On Wednesday 11 February 2004 05:38 pm, zachary goff wrote:
> I'm working on building a homebrew CNC machine and one of my design
> features is to use reed magnetic switches for the home positions. I can
> mount the switch permanently, and stick a small magnet along the table and
> easily adjust the home position, eliminating complex mounting solutions.
> The repeatability is .1mm, not perfect but fine for my setup. Also, be
> sure to look for switches with a built in led that tells you if it is
> active, that way you know exactly when it will turn on, otherwise you can
> install your own led into the circuit.

If you're talking about the kind which I've commonly seen which are enclosed
in glass tubing, I'd have some serious reservations about using them. I've
seen enough of them fail over the years, particularly in those applications
that involved high cycling, that I wouldn't consider them particularly
robust. Note that when one fails, it can fail either open _or_ shorted,
depending on how the glass fractures.

I agree with the comments above - why not consider a slotted opto coupler ?
Low cost, robust an accurate.

Rgds DF UK






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