Please recommend limit switches

[FireFghtr]

Does someone have a source of inexpensive limit switches that can be bought online? Would be for a cnc router.

Thanks
Tom

[Karl_T]

McMaster Carr. great selection, FAST shipping.

[FireFghtr]

I guess I would need help picking out the right kind as well.... i'm not an electrical guy...

[Rance]

Inexpensive? How bout FREE? You could actually make one from 14-2 house wiring (Romex) or a simple paper clip and some screws. These don't have to be 'fancy' switches. Just bend a wire so it makes momentary contact when it is pressed and breaks contact when it is released.

My 2c.

[JRoque]

Tom, do a search here for limit switch topic; there's quite a bit on the subject. Here's one I participated on. In my case, I went down to Radio Shack and bought a few of those alarm magnetic switches. You put the magnet (it has double-sided tape) on the moving side and the reed switch fixed on the axis. Depending on what you use to control the machine it might be as easy as a direct connection to your parallel port input lines. I had to use some lowpass filters which are nothing more that a resistor and a ceramic capacitor - also available at RS - to cut out some noise generated by the drives.

JR

[kaye7877]

Have you looked at automationdirect.com

I sold a bag of 12 - 12mm prox sensors on ebay for $17 a while back. I'm sure I have more stashed around if that is what you are looking for?

[Halfnutz]

Surplus Center has a bunch of different ones, I got a dozen micro style for around 1.25 ea. they work great and are easy to mount. www.surpluscenter.com

[1973ventura]

Where I work we use prox switches for "home" as well as for "overtravel". I have read elsewhere on here that its not good to use prox switches for overtravel or limit but we have no problems using these. We also use photo-eye switches.
Our machines are in wet environments though so a mechanical type switch isnt optimal. We use magnetic prox switches for the most part.

[bret4]

I picked up some of these on ebay. $10 each. I'll see if they turn out to be any good. http://cgi.ebay.com/ws/eBayISAPI.dll...MEWN%3AIT&rd=1

Edit

I got the switches the other day and they look good. I ordered 2 more today just to have some for backups. Can't have enough junk around.

[Shawn Lucas]

Originally Posted by JRoque Tom, do a search here for limit switch topic; there's quite a bit on the subject. Here's one I participated on. In my case, I went down to Radio Shack and bought a few of those alarm magnetic switches. You put the magnet (it has double-sided tape) on the moving side and the reed switch fixed on the axis. Depending on what you use to control the machine it might be as easy as a direct connection to your parallel port input lines. I had to use some lowpass filters which are nothing more that a resistor and a ceramic capacitor - also available at RS - to cut out some noise generated by the drives. JR

How is the lowpass filter constructed? What are the values of the components?

[JRoque]

Hey Shawn,

A simple low-pass filter can be constructed with a resistor and a capacitor. They are also called RC filters; R=resistor, C=capacitor. This combination gives you a cut-off frequency so your low frequency signals - like with limit switches - can pass while the higher frequency signals - like the motor drive voltages - are suppressed.

Using this online calculator as reference, connect the wire coming from the limit switch to the resistor and the parallel port input to the junction of the other side of the resistor and the capacitor. The other end of the cap is then grounded. The values for a 500Hz low-pass are: resistor = 3K, cap = 0.1uF


Note that you want the RC filter as close to the parallel port as possible so it filters out the noise picked up by the wire coming from the limit switch. If you connect it in the control box right before the parallel cable to your PC, you should be good.


JR

[CNCRob]

Here are the ones I use. http://www.use-enco.com/CGI/INSRIT?PMAKA=422-2679 They seem to work pretty well.