Can spindle start when you hit the Z-axis button?

Operator says the spindle came one when he tried to jog the head down using the hand wheel. Is this possible and where do I start to correct this dangerous situation? He said it has happened once before. Machine is a 14 years old Partner 1 with Centurion V controller. We’ve had it since new with all original equipment.

I have a 1997 VM16 that did the same thing. Smithereened an Interapid indicator. Our local serviceman couldn't find the problem, and said "these intermittent things are hard to diagnose". An EE friend said "check all the neutral connections, you're getting a transient somewhere". I tightened every connection I could find, including the X axis connector on the computer box, which was loose and had nearly parted company. I also replaced the X axis servo motor and encoder, which was full of coolant, and put a decent stainless steel watertight strain relief on it. The last act was to place a label on the control panel that says: Do Not Trust Me. I am the only one who operates this machine (one man shop), and S.O.P. is to turn the spindle speed down to zero when it absolutely, positively, mustn't turn on (such as when using a new Interapid indicator). The problem hasn't reoccured since the repairs, but I still treat it like a loaded gun.

Thanks Hickory, very good advice. I’ll check the connections today. We haven’t run any coolant in the machine in years, it’s too slow to do any mold work so we just use it to block up material. The operator lost an Interapid also that I replaced. I’ll remind him to turn the spindle to zero when setting up, that’s a great idea that we should be doing on all the machines.

I like the machine’s size (only 16 X 26 travel) and it’s great for simple set ups. However, it was not one of Milltronics better ideas. It has some serious flaws in design such has this one. I shouldn’t complain too much, we’ve managed to get this far without any major problems. If it wasn’t for its ridiculous lubrication system or lack of, we would invest in upgrading the controller and servos drives.