Guessing from a distance: seperate the 12v supply from the logic/estop
supply. As a check, use a completely different supply - a 12v wall plug
type with adequate power if possible; or a stray computer supply.
Out of curiosity, what is the 12v spindle?

Hul

snafu wrote:
I've got a lashed together 3 axis mill/router.

I replaced the Dremel tool with a 12V DC spindle.
Now the limit switches (wired to the E-stop input) false triggers when
the spindle is loaded rapidly.

I've bonded the spindle supply gnd the motor/controller ground.
I've placed a 0.1uF cap across the E-stop loop at the controller.
I've placed a fly-back Schotky diode across the spindle motor terminals.

By configuring the E-stop for an active low input and shorting out the
switch loop I've proved its the spindle causing the false E-stop signals.

I currently run the E-stop loop open circuit with the switches closing
when the axes travel too far.

Can I simply swap the E-stop pin configuration to active low and run the
axis limit switches normally closed (opening when they are hit?

Any gotchas?

Thanks