CNC Router Build #6 - Limit & Home Switches 

I'm a service engineer for a robotics company.... I'd highly recommend changing the code to home Z axis first, then Y and then X to reduce the risk of tool crashes.

Can't wait for the vid that says: "CNC Router Build: The Final Chapter" where you show of how your CNC Router produces a really excellent design :). Keep up the good work, not that you need to hear that from me because your work is more often than not quite good!

Decent of you to tag big Clive in your video👍

I wouldn't say that individual signals for the limit switches is "pointless" While yes it does require additional wiring & inputs, it does not require additional switches [unless you want to add a discreet home switch]. Also, while machining, it is likely moving in more than one axis at a time, so if a limit is tripped, software cannot easily determine which direction tripped the limit. A part is not necessarily ruined when a limit is trilled either, as it can be a non-cutting movement, due to error in program or placement, that caused the trip. Also having a home different than the limit does not alter the working size of the machine, only shifts the origin. [movement is allowed on both sides of the origin] Some people will place "home" at the center of the machine, instead of a corner. This can be done mechanically with switches, or programmatically as an offset from one of the limits. Having discreet inputs does allow for faster homing [as all axes can be homed at once - not a big issue on a small machine] It can also allow for safe movement away from the limit, but disabling the direction in contention - thus idiot-proofing the machine from the user manually driving against a hard limit, possibly damaging the machine. At a minimum I would suggest 3 limit channels, one for each axis, as then you can determine which axes are at fault in a multi-axis movement [this also allows for homing of all 3 axes at once]. The next step up would be 6 channels, allowing for determination of which extent was reached, allowing for the disabling of movement against that direction in manual mode to prevent damage. Finally I would only add discreet home switches, if you want the home to be a position other than at one of the limits. Having said that, I do enjoy your videos, and the level of detail you go to. Please keep it up!

One other benefit of separately-wired limits is that the home-procedure can home X, Y, and Z at the same time saving a few meagre moments. Certainly not worth it. Well, not unless you have dozens of expensive engineers waiting on your machine, I suppose. Then time is money.

Hi. Your videos are very informative 👌. It'll be nice if you can make a video on points to consider before installing a new switch board from existing circuit as well as new(separate) circuit from the circuit board. Thanks

Thumbs up for a JW - BigClive collaboration?

Thanks for that John, very informative. RobUK

Please share with me Linear Shaft dia you used for X,Y,Z

You mentioned you would add a link to the switches shown in the video. I must have missed it. They seem very robust - can you share the manufacturer / type?

Using mechanical switches for zeroing the machine requires that the precision of the switches (how well they repeat the exact point where they trigger) is better than the positioning accuracy of the axes itself, in your case 1/200 mm, doesn't it? Are these switches really this good?

Okay, but if the limit switches are your physical failsafe, and the controller steps the carriage off onto the limit switch, how can it then reverse the motor to step back the other way if the limit switches have cut power to the motor controllers (or their power supply)??

Yeah limit switches are extremely important

I love your content but you always remind me of a 1940's radio presenter.

Hello Friend. I am in a project to make a cnc table. I still have to wire the race limit switches that go to the card. I have a diagram of the card and the limits. You can help me ? I can send it to you by email. I would greatly appreciate it

John have you joined us on www.mycncuk.com yet?

Please don't write on paper with permanent marker It makes me cringe so much