Hey All,

Ok, here is my dilemma!

I have a Sherline Mini Mill.
Just replaced the motor about 2 weeks ago.
Old motor had bad brushes!
Anyways, everything was working fine.
Then my machine cut out!

The circuit was tripped!
It is on its own dedicated 20 amp circuit.
Went and reset the circuit.
Everything is running well.
I made a few signs.

Then it tripped again.
Now, whenever I turn on the motor (spindle) on.
It trips the circuit breaker!
But, when I plug the motor into a different outlet (different circuit) it works fine!

I did switch to a different circuit breaker on the fuse box (thinking it might be the breaker),
low and behold it does the same thing on a different breaker.

Yet, I can plug any other device into the outlet with no problems.
I even plugged a Iron into the outlet (thinking it was going to trip the circuit) and the iron
worked fine.
Yet, when I plug the spindle motor in, it trips the circuit, in a matter of milliseconds!

So I am totally stumped here!
Anyone have any ideas?

Check for ground on the motor, is this a Universal or permanent magnet field DC motor?
to check the drive, use a 100w lamp or similar load in place of the motor.
Al.

Al,
I checked the ground and it is ok.

But, when I disconnect the ground, it works fine.
Evidently, the other outlet I tested it on, was not grounded.

Why would the motor and speed control work fine, when not grounded.
If I hook up the ground, it shorts out!

Hmmmm?

Try it with the motor disconnected and the dummy load, if it trips the problem is a ground in the drive, if only when the motor is connected then the ground is on the motor, it will not be safe to use if there is a ground leakage and you have no ground conductor.
Al.

I've had the centrifugal starter contact board come loose inside a motor before. It lodged itself in such a manner that it still worked but intermittently shorted to ground.

Is this a brand new motor or a new to you motor? Is is motor from Sherline?

Hey Jeff,
Yes, it is a brand new motor direct from Sherline.
I just purchased it a month ago..
My original motor, the brushes went bad, (used it for 7 years). Tried to replace the brushes, but the board the brushes sat on broke. (evidently, a lot of people were having this problem).
Now, Sherline, has a new motor with the brushes on the outside, so you don't have to disassemble the whole motor to get at the brushes.

I guess it is a new type that Sherline is using.
I think I was one of the first to get the new type of motor.
It is a Hill House Product motor.

I noticed when I first got the motor it was running real hot!
I told ,Kat, at Sherline, and she said that was normal for that motor.

I isolated the problem to the motor, though..
I think the new motor has a short somewhere in it.
It worked fine for a little while, then it quit (tripped the circuit) one time on me.
Then ran fine for a while, now I can't even turn it on without it tripping the fuse.

Now, if I disconnect the ground it works fine.

I am going to call Sherline this morning and get a exchange.