Electrographite grades have lower thermal expansion coefficient related to copper grades. Thanks to this pyhsical property, clearance between carbon brush holders and brushes should be minimum. Especially Electrographite grades are used in DC Motors and Generators.
On the otherhand, copper grades expansion are high according to its copper content. Copper is metal and expands with heat. High copper content means high thermal expansion. Because of that reason copper grades have to be much more clearance between holder and carbon brush.
However, if a the clearance is out of limits, in this case carbon brush can stuck with heat or vibrates with action.
Production quality and company standarts are very important. You should work with reliable companies to get better results.
Carbon brush holder position also very important parameter to use carbon brushes properly.
We can start to examine carbon brush holders position with the gap between lower side of holder and commutator / Slip Ring tangent. It should be between 2-3 mm up as shown in Figure 2.
This gap is compulsory for all types of machines (DC Motors / Induction Motors and Generators). Otherwise carbon brushes wear excessively or holder can damage commutators.
According to literature the alignment especially in DC Motors is very important parameter to get succesfull commutation.
You can see from Figure 3. Brush arms should be parallel to each other. Check the distance between all the brush arms is equal. This is valid for brush arms without circumferential stagger.
Sometimes motors work with missing brushes or in some situation brush holders are more blocks than actual carbon brush quantity. In this case staggered mounting occurs.
You should follow figures on right handside to avoid electrical damages.