limit switch recommendations for hobby level CNC conversion of a HiTorque mini mill

I'm planning to do a CNC conversion on a HiTorque Mini Mill from Little Machine Shop. The first mill conversion I did was a Proxxon MF70. For that one I used mechanical limit switches. The stepper motors are small so in the event it doesn't stop I can, with a little difficulty, back off the axis lead screw enough to free so the motor will move the table. For the new conversion I was looking at high torque NEMA 23 motors. I'd like to try something little more reliable than a micro switch one each end of the axis. Am I overthinking this, or is a "good" mechanical switch reliable enough for a mini mill? What is being used out there with self converted CNC mills?

I really like these; https://www.ebay.com/itm/5Pcs-TL-Q5M...QAAOSwbdpWUtNA

They are potted and do well with coolant. More importantly, they are fairly compact which helps with mounting on a small mill, though perhaps not as small as mechanical units. I get <.0005" repeatability, which is well below my backlash, so take that for what you will. It took a bit of experimenting to get there. I use mine with the targets running parallel to the sensor face, rather than moving towards or away from the sensor face. I just needed a nice square and flat target, so I've been using some steel angle for that. This is on a G0704.

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Originally Posted by jrdarrah

Am I overthinking this, or is a "good" mechanical switch reliable enough for a mini mill?

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Well, ''good'' mechanical switches seem to work just fine on industrial machines. I have three machines in the shop with 30 year old mechanical switches, still working just fine. They have lived their life bathed in coolant, way oil, and chips.

Just about anything you want in limit switches. https://www.automationdirect.com/adc...limit_switches

Thanks for the information. My mill is on the way, I'll look into these switches but since I'm using a Raspberry PI CNC shield I need one to work at 5VDC so I don't need additional interfacing or an extra power supply.

Thanks for the link. Once my mill gets here and checked out I'll start thinking about the CNC conversion. Automation direct seems to have enough variety that I can find something that will work.

With a mechanical switch there’s no need for a voltage at all. The switch either has continuity or it doesn’t.

Agreed. I was wanting to get something more reliable than micro switches which is what prompted my question.

Repeatability is the number one concern for me. After that, price. From there, it's reliability.

I initially used mechanical switches, but I never could get the repeatability out of them that I wanted. This almost certainly was due to a lack of inexperience on my part. When I switched to proximity switches everything improved, but it was also version two of the build. Over the years I've fine tuned my setup and repeatability is under .001". That's well under my backlash which is around .002" on all axis, and if I flex on my G0704 well then things start to move, even with ways really nice and tight. I think mechanical switches are easier to setup, you can run them in series very easily, and they are dirt cheap. Proximity switches perhaps have the advantage in that you don't have to worry about damaging their switch arms. However, as Jim points out, when properly applied mechanical switches work just fine and do so with great results. So do what you feel is most desirable.

Hi,
I know a lot of people like to have ALL their limit switches wired in such a manner that they occupy just one input of your controller.
With mechanical switches that was easy, just wire the NC contacts in series.

With proximity switches you cant wire them in series. If you used NO prox switches you could put all six in parallel and tat would allow you to condense
all your limits to one input.

I personally don't like trying to condense limit switches to one input. It used to be common and mandatory if you had but one parallel port controller but modern
controllers often have 15 or more inputs so there is no need to do so. I'd recommend six prox switches, each with its own input to the controller, as limits and
another three separate switches for homes, there again each with its own input.

I use roller plunger microswitches for home switches, I like and prefer the hysteresis they offer and prox switches for limits.

Craig

How did it end up with the mill?