Figure 3-11. Internal wiring diagram.

strip of 5/0 sandpaper against the commutator to

polish the surface and remove burrs which might

have been left by the undercutting process. Stop the

lathe and set up a dial indicator gage to check the

accuracy of the finished commutator. The

maximum allowable eccentricity after polishing is

0.0001 inch total indicated run-out, and 0.0005

inch bar-to-bar.

f. Balancing t h e A r m a t u r e . A f t e r t h e c o m -

mutator has been refinished, check the armature

for proper balance, which should be within 20-

grain inches at each end. If a balance correction is

required, mill the retaining bands 0.032 inch deep

with a 0.25 inch diameter cutter. Mill until the

proper balance is obtained.

g. R e a s s e m b l y .

(1) Install new brush springs (4, fig. 3-10) to

brush holder assembly (1). It will be necessary to

wind each spring approximately 3/4 turn in order

to slide it on the spring support bar of the brush

holder (6).

Figure 3-11. Internal wiring diagram.

Do not wind spring more than necessary

e. Refinishing Commutator.

to engage into position as spring may

(1) Equipment required. To recondition the

take a permanent set

commutator within the tolerance limits, the work

(2) Install studs (5) to brush holder assembly

must be performed on a good lathe accurately set

(l).

up and adjusted. The commutator end of the ar-

(3) Slide the insulating tubes (9) into holes in

mature shaft should be supported on a bearing

support (10), and after coating both sides of in-

which can be used as a master by lapping out the

sulating plates (8) with insulating resin, assemble

inner race to obtain a slip fit to the armature shaft.

while still wet with brush holder assembly (1) to

The bearing should be supported by the turning

support (10).

center to support it in the tail stock of the lathe. The

(4) Slide an insulating washer (7) and washer

splined end of the armature should be driven by a

suitable collet or held on a center in the head stock

(3) over each stud and secure with nuts (2).

and driven with a lathe dog.

NOTE

(2) Making the cut. Adjust the lathe speed to

The brush holder assemblies must be

rotate the armature at approximately 600 rpm and,

p o s i t i o n e d so that brushes will be angled

toward direction of armature rotation.

using a sharp carboloy tool, take the lightest cut

possible with a fine feed. Remove only the amount

(5) Apply insulating resin over insulation and

o f material necessary to true the commutator

support (10), extending at least 0.06 inch from

surface. This may require making several cuts since

b r u s h holder insulators. Bake for one hour at

no more than 0.002 inch of material should be

150 F.

removed at any one time.

(6) Slide inner baffle disc (46, fig. 3-9) on

drive end of armature assembly (48), making sure

When new, the outside diameter of the

that hub of disc projects away from ball bearing

commutator i s 3 . 3 1 2 i n c h e s . W h e n

(53). Carefully press ball bearing (53) on drive end

repeated turning reduces this diameter

of armature until inner race of bearing in flush

to less than 3.187 inches the armature

against baffle disc. Install outer baffle disc (46) and

must be replaced.

replace retaining ring (43).

(3) Undercutting the mica. Using a reliable

( 7 ) Carefully press ball bearing (51) into

undercutting machine, undercut the mica between

bearing and brush holder support assembly (52),

the commutator bars 0.032 inch deep by 0.052

pressing only on outer race of bearing.

inch wide. Using a triangular scraper, remove all

( 8 ) Position retaining ring (49) over ball

sharp edges and burrs from the commutator bars.

bearing (51) and secure with screws (50). Lock

Remove all metal chips and mica particles from the

wire screws in pairs.

slots with a bristle brush and compressed air.

(9) Slide baffle disc (47) on commutator end

(4) P o l i s h i n g t h e c o m m u t a t o r . W i t h t h e a r -

of armature assembly (48). The hub of baffle disc

mature rotating at approximately 600 rpm, hold a

must project away from ball bearing (51).

3-16