I have an older Unisaw with a 1 hp Bullet motor.
It started acting up today. When I turn it on, it runs at reduced speed
for about 10 seconds, then kicks in to hi speed.
Sometines when it is turned on it just makes an unhappy hum. I then
rotate the blade a bit, and turn on again, and it starts and runs at
reduced speed for about 10 seconds, then kicks in to hi speed.
When it is running at reduced speed, the brushes (lots of brush left)
arc a bit. When it kicks to hi speed, the arcing stops. I think the
brushes might be just for starting.
Anyone familiar with these motors, and have an idea of the problem?
Not familiar with this exact motor, but the construction is generally
similar to all induction motors.
I would check the start cap - it is probably leaky.
The "brushes" you refer to are probably the centrifugal start switch.
Both are removed from circuit when the motor reaches a defined RPM.
I believe the OP is talking about an old repulsion-start motor. These
don't use a capcitor. They have an armature & brushes to provide
starting & low-speed torque. There is usually some sort of arrangement
to lift the brushes when the motor comes up to speed and then it runs
like any other induction motor.
Because of their torque characteristics one of these motors
rated at 1.5hp could be used where today a 3hp cap start
induction motor would be used. (Not saying that they have
equivalent power, just that it would be usable)
They would be expensive to manufacture today, compared to an induction
motor of equivalent utility, and as far as I know, no one does
manufacture such a motor.
Try cleaning any sawdust out of the motor first, then make sure that
the brush lifting mechanism, springs, etc, are OK. How does the motor
feel when you spin it by hand with the belts removed?
No dumb questions, just dumb answers.
Larry Wasserman - Baltimore, Maryland - firstname.lastname@example.org
Yea, you're probably right.
It was three in the morning and I just tossed that out. Haven't seen
one of those since childhood - and that was a while ago, when cars
still had generators...
Always rebuild my own alternators/starters/motors/etc - refusing to
spend my time installing/uninstalling/returning defective third world
import rebuilds. It's a stubbornness thing... but haven't been towed
or DOR since 1978.
Likely a maintenance nightmare in a dirty environment.
Given the more accurate description of the motor, the troubleshooting
choices are probably one-to-all of the following: brushes worn/too
short, springs have lost tension, centrifugal release is fubar'd,
commutator is eroded, or the rotor winding has a shorted winding - not
uncommon with old, fatigued insulation of that era.
If a visual inspection reveals nothing obvious, take it to a good
motor rebuilder (are there any left?) and let them check the current
draw/brush mech and such, and for safety/durability be sure to meg it
Delta "Unisaws" do not use 1 hp motors and their motors don't have brushes
either. The smallest motor that I've ever seen on a Unisaw was 2 hp and all
Unisaws were manufactured with induction motors and they don't have brushes.
If your non-Unisaw motor has brushes, then the problem is likely to be bad
bearings or worn/damaged brushes and a bad commutator (the contacts on the
armature that the brushes rub on). If the motor has been over heated and the
windings have been damaged, then this is also a likely cause of your
problem. Does the motor have a bad burning smell to it? Did it smoke the
last time that you used it? If so, it's time to go shopping for a new motor
or maybe a whole new saw. If not, then you can have the commutator cleaned
and dressed (resurfaced) and then replace the bearings and brushes and your
saw should run OK again. All of this work is best done by an electric motor
shop or dealer service facility, if you haven't done this type of work
"sailor" < email@example.com> wrote in message
saw for a short while, and from what I read, in the groups, it sounds
like is is an
orig. 1 hp motor. Aparentlly is called a repulsion-induction motor, and
are used for starting. This motor has brushes, and says delta on it. It
says 1 HP.
And the switch plate says Unisaw. It's looks almost exactlly like a
that this ones base is cast iron. It was made in 1946. It even smells
lkie a Unisaw,
sooooooooooo it's a Unisaw.
The motor doesn't smell, or smoke. It's like the run circuit doesn't
kick in and the
start circuit keeps running.
That's assuming there is a start and run circuits!
Thanks for the ideas.
Charlie was talking about "modern" (i.e. those made in the last 40 years or
so) Unisaws. Those sold these days have 3hp or more motors.
Repulsion-induction is short for repulsion start induction run. This design
takes advantage of the fact that a series wound DC motor will also start and
run on AC.
At startup, brushes conduct electricity to the armature. When the motor
speed gets fast enough, a centrifugal switch withdraws the brushes. From
that point onward,
the motor acts in induction mode. It is possible that the brushes do not
retract; thus the motor does not enter the induction mode. You should take
the motor to a repair shop for investigation.
High maintenance is the principal reason that repulsion-induction motors
fell out of favor. These motors have the lowest starting current, and that
is their principal claim to fame.
My experiences with repulsion-induction motor is with a 3 horsepower air
compressor in an autobody shop. The motor that we had did NOT supply
electricity to the brushes, they were connected together to "short circuit"
the armature. They could be adjusted by rotating the brush holder clockwise
or counterclockwise to set the amount of starting power needed. If I
remember correctly there were 4 brushes spaced equally around the
commutator, but I am not sure if they were all connected together or in
pairs. When the motor reached its correct RPM the brushes lifted off the
commutator and the motor ran without the brushes. This is why the brushes
would last a long time because they were only in use for a second or two
when the motor started up.
Only universal or repulsion-induction motors have brushes. What does the
motor plate say?
The brushes in a repulsion-induction motor are only used for starting. They
retract as the speed goes up. However, as this type of motor was
discontinued in the 1950s, your motor is quite old. Of course, such motors
are still repairable.
After calling 2 motor shops, and getting no suggestions from 1, just
bring it in and we will tear it apart. The other shop told me it could
be the circular switch on the end of the commutater. He said it might
just need to be cleaned, but to be careful taking it apart, as there
are a lot of small parts.
I took the end off the motor, while it was still on the saw. As I
started to remove the end, I remembered to mark the end and housing,
for alignment. I did this after moving the end a little.
I removed the e hold down screws that hold the brush assembly, so the
brushes would stay in place.
I found that 2 of the 4 brushes were sticking in their brush holders. A
little solvent, and light sanding, and after it was back together, it
worked! At first it didn't start and looked like it wanted to turn the
wrong way. I loosened the brush ring screws and shifted the ring about
1/16" and all was perfect. I must have moved the motor end a little
before marking it. Adjusting the brushes took care of it.
I didn't get into the switch.
If you have a Bullet motor,or other type, keep this in mind if yours
I guess I'll have to buy the saw a present! New miter gauge sounds
Nice you fixed your old moter. My dad used to sell the Delta line in
the late 30's and early 40's in LA. He had a 1941 Unisaw with a 1ph
repulsion induction motor. It was still working fine when my son sold
it about 10 years ago. I have some old Deltagrams that advertise the
saw, $50 for the saw and $50 for the motor. These deltagrams are from
the same time. For those who have forgotten, the Deltagram was the
little magazine Delta published to promote woodworking and their tools
with projects in them around the advertising and pictures of peoples
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