Commutator:
Unit must be in good condition, with less than .002" out-of-roundness. Bar edge must be chamfered and there should be no burned edges.

Brush Holders:
They must be mechanically sound and permit the brush to slide freely. Brush holder fingers must move freely and if the unit consists of constant pressure springs, these springs must be in good condition. Springs that are difficult to move, have an excessive accumulation of carbon, or are worn, will cause excessive brush wear.

Brush Holder Angles:
The angles should be set to the original manufacturer's specification. Any more than a 2 degree variation in the setting can cause arcing, bar burning, and excessive wear. Brush holders that vary in the angle set to the commutator will cause the unit to be "off neutral".

Brush Holder Spring Tension:
Maintaining the proper spring pressure reduces arcing, brush wear, heating, and commutator wear. Light spring tension can cause threading and definitely will shorten the brush life. As a general rule, we recommend that the brushes be set at 4 psi pressure. To calculate the pressure, measure the width and thickness of the contact face and calculate as follows:

Pressure in Pounds/Brush = (Width x Thickness x 4 psi)

Brush Holder Quartering:
To insure that the best machine electrical neutral can be achieved, the brush holders must be quartered. Quartering is setting the brush holders at equal distance around the commutator. For a 4 pole machine, the spacing will be every 90 degrees. If the quartering is not properly set, you may experience excessive arcing, heating, brush wear, and commutator wear.

Machine Neutral:
To obtain optimum machine performance, the brush must be set at the machine electrical neutral. If the unit is off neutral, you may observe sparking under a no-load condition. Depending upon how far off neutral the machine is set, there may be arcing and bar burning.