I have a 1984 Bridgeport Boss 4 three axis that has been sitting idle
in storage for 2 years. I just pulled it out and tried to put it
through it's motions and the spindle won't power up. I know the trick
about making sure it has spindle oil so I don't think it's that. The
axis' move fine, everything else powers up. when you try to turn on
the spindle you hear a buzz from the electrical box.
Thanks in advance
Probably a sticking contactor. Possibly a corroded contact
in one of the motor overload heaters. You might try (with the
POWER OFF!!) going in the enclosure and working the contactors
manually. Most of them have some way you can get a finger or a
tool in there and pushing the magnetic armature to drive the
contacts closed. Many have a rubber damper to absorb the thump
when the armature drops out, and these can get sticky with age.
The heaters usually follow the contactor. Find the contactor for the
head and identify the 3 leads in (generally from the main machine
breaker or fuses. Then identify the 3 lines out which go to the
overload relay. Check for power coming to all 3 connections on the
contactor; loose wires do happen.
If you have the proper power coming into the contactor I would
disconnect the 3 output wires to the overload, try to activate the
spindle motor, and check to see if you have power passing through all 3
internal contacts to the output terminals you've disconnected. The
reason for disconnecting the wires is to prevent a false reading on any
of the terminals which can be caused by power flow through the motor.
If all you get is buzzing from the contactor at this point you may have
a bad coil in your contactor.
If you find you have a proper connection through the contactor then
replace the 3 wires and disconnect the 3 output lines at the output of
the overload relay and check for a proper current path through it. If
this should check good then check the lines and connections between the
overload relay and motor and finally the motor itself (can you turn the
If you could scan and post your electrical schematics it might help us
understand your circuit. I understand there is a metalworking mailbox
around here somewhere. Good luck.
Just to be sure -- let me ask some questions:
1) Can you turn the spindle by hand? If so, is it easy.
2) If so, then is it possible that the belt has failed, and the
motor turning with no connection to the spindle may be the
buzzing which you hear.
The overload heaters, if any one of them (there should be *at
least* two, and possibly three) has overheated, it will open the wiring
to the coils of the contactors to prevent *any* buzzing sounds. (Of
course, if the heater coil itself has burned out, then you would get
power only to two of the three phases, which would leave the motor
buzzing.) If you can spin the motor by hand just before switching on
the motor power, you should see the motor spin on up -- if the problem
is loss of a single phase somewhere in the wiring.
Note that at least my old BOSS-3 has a more complex contactor,
actually two contactors mechanically interlinked, so one closes to run
the spindle forwards, and the other closes to run the spindle in
reverse. The mechanical interlink prevents both from turning on at the
same time, and blowing all the fuses.
Speaking of fuses -- have you checked the three cartridge fuses
just before the master power switch on the back?
The BOSS-3 (and presumably the BOSS-4, 5, and 6 -- the stepper
motor axis ones) have each axis powered from a different phase, so if
you can jog all three axes, you have full three phase power.
That is "the dropbox". Go to:
and read about how to use the dropbox (one of the click-on options).
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