Re: Stepper Dissasembly

Group,
I have been following this thread for some time. I worked
for several years running a department that made and repaired DC
motors and steppers. The rotors were magatized using a very large DC
power supply. In the power supply there were banks of capacitors,
large switching SCRs and a timer. The fixture the rotor went in,
looked like the inside of a stepping motor only larger. The rotor
was put in and then it was lined up with a mark, a button was hit. A
large jolt of current would run through the fixture magnetizing the
rotor. Before you would pull the rotor out of the fixture the rotor
would receive a ring or an old field assembly.
During repair you put a ring shaped keeper over the rotor shaft.
As the rotor is pulled out of the housing it goes into the keeper.
This prevents the magnetic field from being reduced.
A magnetic field is like making a whirlpool in a swimming pool.
As long as nobody swims the wrong way everything is fine. In a magnet
all the electrons are orbiting in sync. Forget that tiny magnet theory
they tought you in school. The magnet field is created because the
spinning electrons destort space and time. (nobody really knows!)
New motors have their coils wound on a machine that is
automatic or it can be done with a manual winder with a counter. We
are talking turns of wire not resistance. With a good grade of wire
and the proper turns, correct resistance per phase just happens. When
making a motor or repairing one, the most important thing is the
direction the coil is wound in. If a coil is wound in the wrong
direction the electrons orbit the wrong way causing the North and
South pole of the phase to be backwards. You now have a kid swimming
the wrong way! The motor will not work correctly
Modern stepping motors have magnets that resist demagnatizing
compaired to older ones. All stepping motor magnets will grow weaker
over time. A good design takes this into account. Some companies like
to run their product at the edge, so people who look at the spec sheet
will buy their product. Great designs make great surplus.
An other thing you will need is a bobbin. Wind your new wire on
a piece of cardboard shaped like a long "H". This lets you thread your
new wire on field coils in tight places. Make sure you use the correct
diameter of wire. Save the old wire and measure it's length. Wind the
new coil with the new wire. Make sure you wind the coil in the right
direction.
Metal particles can be removed using double stick tape,wax rod,
plastic or brass tweezers. Some motors are easy to be rebuild while
others were designed to be thrown away. I know a man who is 75 years
old and he sill rewinds motors for a living. I showed him this
conference. He said: "People who sell new items don't like to hear
the word REPAIR!" Before you throw that motor away, at least open it
up and look at how it is made.

Bob Watters

--- In CAD_CAM_EDM_DRO@y..., mariss92705@y... wrote:
> Hi,
>
> I understand your point of view, but I have to deal with situations
> when "junk goes wrong".
>
> I had someone (no one on this group) that hooked up and destroyed 6
> drives in succession on a motor he had liberated from a dumpster. I
> had him send me the offending motor and it had a shorted turn on
one
> phase. An ohmmeter wouldn't show it but an inductance bridge did.
>
> One "free" motor and six dead drives.
>
> Mariss
>
> --- In CAD_CAM_EDM_DRO@y..., "Art Fenerty" <fenerty@h...> wrote:
> > Hi:
> >
> > Just my two cents worth...Never listen when someone tells you
> something is
> > junk. I have dissassembled and fixed just about anything
including
> countless
> > items that are "Do not take apart. It will never reassemble"
able.
> I have
> > taken apart dozens of stepper motors, reassembled, and run them
for
> lengthy
> > periods of time with no noticeable problem. Its the same thing
with
> rewiring
> > the SloSyns, some folks said, they will never work, you'll only
get
> one RPM,
> > You'd need 400VDC, the formula's prove.....etc.
> > I just sit and watch them work great and smile.
> > The only rules in hacking something together is...there are no
> rules. If it
> > works, it works, if it don't, you learn something. Just don't let
> the smoke
> > out, its hard to buy surplus smoke to replace it with.
> >
> > Art