David
Here is what I had to say about homing and limit switches.
On my Tormach 770 CNC milling machine in order to be able to use machine offsets I have to reference or home the machine before I can do much.
If you have a part that you run each day and have a fixture that the material for the part is clamped into you need to reference or home the machine every time you start it so that the machine then knows where that fixture is located on the table. That position is a machine offset and can be stored using G54 to G57 offsets.
Homing tells the software where X0,Y0 and Z0 are. Then if you have G54 set to machine coordinates X+5" Y+5" this becomes X0,Y0 for G54. Now if you clamp a 6" piece of material so one corner is at this position and tell the machine to machine a smiley face in the middle of the piece it will do it every time you put a new piece of material at the same location.
As has been said the only time that the switches you presently have installed on your machine do any thing is when you tell the machine to home or reference the 3 axis. Once that has happened the software will no longer react to one of those switches being activated.
Until you install additional switches on the other end of X and Y and configure those switches as limit switches and configure the switches you presently have installed as both Homing and limit switches you will continue to crash into the hard stops for you machine.
With a brushed DC motor as your spindle with all the electric noise they generate you have to find ways to negate that noise so you do not get false readings.
Hope all this helps. feel free to ask more questions.
And yes homing and limit switches configured correctly are very important on CNC machines.
Dave