Fitting and Bedding Carbon Brushes

Fitting and Bedding Carbon Brushes

When fitting a full set of carbon brushes on a machine, it is very important to bed the brushes to assure a full contact area with the commutator or slip ring to avoid overloads. There are few ways to bed carbon brushes, the most common is with a Brush Bedding Stone in which case the particles of soft grinding stone will grind the brushes to a perfect radius and a perfect contact face. Once the brushes are bedded, the machine should be stop and clean thoroughly. Lift brushes from the brush holders and by means of blowing air, clean the area where carbon brushes made contact with the commutator or slip ring to ensure that no grinding dust is set between the segments of the commutator or in the surface of slip ring.

Other means of bedding carbon brushes is to fit an emery cloth around the commutator or slip ring, fit carbon brushes on brush holders applying pressure with spring finger, rotate commutator or slip ring slowly in the direction that normally operates. If commutator or slip ring can not be rotated, then place a longer strip of emery clothe under the carbon brush as mentioned before and do one carbon brush at a time by sliding the emery cloth back and forward until desire radius is achieve.

If single brushes are replaced, for example 16 brushes per set, 4 per arm and you replacing one brush per arm, then is no need to bed brush replaced as it will bed itself and the other brushes in that arm will carry the additional load until full contact is achieve.

Seating Stone – Correct

Sandpaper – Incorrect

Sandpaper – Correct


Please note that this and other maintenance suggestions must be carried out by a qualified electrician or otherwise if not always make sure that the machine is properly isolated before any work is done.