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confused about home and limits...
« on: January 17, 2011, 10:43:02 AM »
Hello everyone :)

I recently handbuilt my first cnc machine, I'm rather excited about it. I eventually plan to try and make my own guitars with it, but at the moment I'm happily trying to get the bugger to work!

So far I've built it, I've got my motors and all that attached.I've got reliable movement along all of my axis (3). I've calibrated the motor turning to get accurate movements.
(I'm quite proud of myself so far :D)

The next thing I want to try and figure out is how home and limits works. My controller card/breakout board gubbins has wiring for 3 limit switches and 1 Kill-switch.
I've got a Kill switch and 6 limit switches on the way.

Are the switches wired up in pairs in series/parallel to the controller? (2 for x, 2 for y, 2 for z)
I'm guessing I put my limit switches in position, configure them in Mach3 to kill that axis should they get triggered.

Can I then set it to move to a furthest point, say the furthest back/left/upper corner of my cutting area, stop when it triggers the switches and then consider this point to be 0,0,0. I can then set my soft limits of the cutting area I want to use and design my CAD files around the principle of my cutting area and my 0 point?

I'm quite new to this whole buisness and am learning as I go, Sorry if I come over a bit noobish :)


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Re: confused about home and limits...
« Reply #1 on: January 17, 2011, 11:12:28 AM »
You can wire the switches for each axis in pairs (series) or you could in fact wire all switches in series for all axis and only use one input, makes no difference to Mach as when it sees a limit it will E-Stop no matter which switch is seen. You will need to use the normally closed contacts on the switches for this, also it is much safer to use normally closed as opposed to normally open, the reason being if a switch or wire breaks Mach will E-Stop, if you were using Normally Open switches and a wire broke Mach would not know and the axis would just sail past the switch as no signal would be sent to Mach due to the broken wiring.

You can do what you say regards the home if you enter that switches port and pin number as a Home as well as a limit. You can home to any position you like to set Home but the convention is that tool at lower left of work area is machine X and Y zero. Thats not to say you actually have to move there to set that position as machine zero, you can move totally opposite corner and just set a home off value for Mach, that would mean that the machine coords DROs would show the distance the axis is away from machine zero when you home.