Hi there,

Limits aren't that difficult but to a degree the way you implement them depends on the facilities offered by your breakout board... or in your case the Dsub board... there are usually about 5 pins dedicated to input, which looking at the pic I can see the Dsub board has. In your CNC control software you will be able to assign functions to these inputs based on pin numbers.. Estop , Limits or Encoders are usually the functions assigned.

Just looking at limits they operate as follows:- Use a normally open switch, when the software detects any of the assigned inputs switching closed it stops ALL motors. In the case of Estop it similarly stops ALL motors. Shared Home/-ve limits operate slightly differently to just a simple limit. When homing the control software moves each axis until the switch is triggered then advances a small amount off the switch to a known position. When NOT homing if the shared switch is triggered then ALL motors are stopped as with a bog standard limit. A lot of this is down to the features available in the software you plan on using. It's one of the reasons I went with Mach2/3 myself as it has ALL the bells and whistles IF you want to implement them.

It's usual to assign a separate input for each axis home position/-ve limit, this uses 3 inputs. Then a further single input can be used for all +ve limits, this is called summed limits. The remaining input can be used for a separate Estop or enable function... again on a normally open switch. If you plan on using the inputs for other purposes it is possible to sum the home/-ve limits too... but then you have to ref each axis 1 as a time instead of being able to ref all.

I've upped a rough diagram based on a pic from your build log with suggested trigger/switch positions. I'd mount the switches to the base/frame so that the blocks of your moving parts would trigger the switches or you can preferably use adjustable trigger blocks. This avoids having the wiring to the switches in motion and also means it's easy to move the trigger block to adjust the point at which the limits are switched. You don't have to use expensive cable for limit switches.... they are normally open for starters so there's no signal/voltage in the circuit anyway. micro switches are as good as anything.. I use micro switches on my Y axis and Z axis and have excellent positioning and repeatability which I've tested using multiple-passes over the workpiece.

If there are no docs related to limits etc with the hardware you bought then I suggest a good read of the Mach2/3 manual which has a good discussion of the subject and you can then relate this back to your own hardware.

hope this helps

oh BTW... I notice you are located in Wigan... I used to, work down the road in St Helens up until 1989.. for a firm called Sutton Timber.. maybe you know the place as it's a sizeable timber/UPVC fab setup.. then again maybe not...