Book 3

ests with its heavy side down. Note, however, that a nick on the
edges or wear damage on the shaft can also cause the arm to stop in
certain positions and fool you. To avoid this, try the armature several
times in different positions in different places on the blades. If the
same pole (mark them A, B and C for easy identification) always
'hangs down', your arm is obviously out of balance.
NOTE: an even better method, especially with small amounts of
unbalance, is to lean the wood piece with the razor blades slightly
and have the armature roll down them slowly. If the arm rolls with
the same speed, the static balance is OK. But if it rolls in a 'calypso
rhythm', work is needed. Let us start with method A , removing
weight from the heavy side.
There are different ways of doing this, as the photos will show.
The old Champion balancing, grinding off big slices, is the worst. It
will short circuit many plates and make for higher core losses due to
eddy currents, as explained earlier.
The Dyna method of filing notches will short circuit less plates, but
still leave a rather long scar in the pole face.
The best way of removing weight is by drilling holes, since the
least pole area will be disturbed. All motors of quality (Champion has
switched to this method on its new series) have this kind of
balancing.
However, drilling holes in the hard pole surface without slipping
accidentally into the wires is not easy. Experience speaks. Therefore.
I recommend the beginner to use the notching method instead, by all
means use holes.
Having determined which of the poles is the heaviest, the armature
is clamped in a vice with this pole up. Use inserted pieces of thick
paper or similar, so that the arm will not be marred by the jaws or
the vice. Now grab a thin round file and start working away, holding
it as in the photo (less risk of driving the file into the wires). Please
note that the notch must not necessarily start on the middle of the
pole face (cross-wise), but rather on the exact part of the pole that
is pointing down.
NOTE: always, however, file on the middle of the pole face, lengthwise,
or you might risk further damaging the dynamic unbalance.
Should the notch threaten to grow too big, it will be better to make
two smaller notches beside each other. But don't forget to check the
balance often, so you won't remove too much!
If you use holes, these should be about .05 to .10 in. in diameter
This will depend on the amount of unbalance. If the hole is somewhat
to the side of the pole, don't drill it too deep or you might cut a few
wires.
If you consider it for a second, employing method B and adding
weight to the light side is really much smarter. Notching or drilling in
the poles means less magnetic mass, and though the armature will
run faster when balanced, we have actually lowered torque. Method
B means more (dead) mass, but provided the unbalance, and thus
the mass needed is not too great, we have made an overall gain by
retaining torque.
The method has its limitations; it cannot be used on 'fullhouse'
winds, as there must be space for the weight we are going to add.
Otherwise the method is a simple one.
For best results, we should start while epoxying the armature.
Mix up some epoxy, same as the one used on the armature, and put
it beside the solder iron for quick curing. Then get out some lead
sheet and start filing on it, until you have a nice collection of lead
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