[nateman_doo]

So I am sitting here trying to figure out a new system because my current home/limit switches are way to susceptible to false readings due to moisture.

Has anyone every used something like a dowel pin mounted into an acetal type block? The idea is to electrically isolate the dowel pin from the table, but when the table bumps into it, it would stop. The micro rocker switches are not very accurate.

I am curious if such a system exists?

[Al_The_Man]

Well the principle has been around for eons, a microswitch in a sealed enclosure and is tripped with a plunger that traditionally has taken many forms, depending on the application?
Why the electrical isolation? normally with MicroSwitch the contacts are not part of the operator?
Al.

[nateman_doo]

I guess the fluid that gets in there is what triggers a false reading and the table stops.

If I had a tall rod, that the table will "bump" into when it touches it, it will send the ground pulse required to stop the machine properly.

[TXFred]

There's no reason that won't work. You're just replacing the microswitch with a much larger switch.

It does sound bulky, and therefore is prone to being bent, tweaked, or otherwise knocked out of position by accident. If you want repeatable homing, this may not be the best method.

Frederic

[nateman_doo]

I am thinking like 1" thick, and under the table touching the carriage, or someplace that it won't interfere. It doesn't have to be a rod, it can be any piece of conductive metal (likely aluminum) that is electrically isolated from the rest of the table, that will ground out when the table bumps into it.

In any case, I would love repeatable homing.

[Al_The_Man]

I use these hermetically sealed Microswitch.
ebay 390370013513
Al.

[keebler303]

Nateman

Your proposed design would not allow any overtravel which may be bad news if for some reason a wire became disconnected during homing. If you use the right switch, it should be quite repeatable.

Matt

[LongRat]

The overtravel problem is a real one. You'll need to back it up with a preloaded spring assembly. Even during normal homing operation there will always be a delay (even if very small) between when the home switch fires and when the axis stops. A totally rigid assembly will be stressed unless you implement some compliance in it.
You'll also need to ensure it stays dry. Any beads of moisture on either conducting surface will cause the switch to trigger early. Sounds like a decent idea but I am pretty sure it would be easier to install a sealed switch, as Al has done.

[nateman_doo]

Al's switches are $20 per axis. I have enough scrap to make the poles. I will get the switches for my larger machine, but one day when I get fed up with the false stops I will try to make a acetal stop.

I already took measures to waterproof the current switches, but its hard to stop moisture.

[digits]

What about magnetic proximity switches? They're totally sealed and non contact, but I suppose you might have some issues if you get magnetic swarf on them...

[gd.marsh]

Nateman,

Are you certain the false trips are not due to noise?

I had some issues with that when I first got my machine running & was seeing lots of unexpected stops.

Don't know about your level of knowledge on the subject, but there were some wiring issues I didn't fully understand. Especially concerning the difference between a neutral & a ground.

It's taken me a while to sort things out but now that I have my machine is running quite reliably.