Use a toothbrush and contact cleaner to clean the commutator. Spray the contact cleaner on the commutator and stir the surface with a toothbrush. This will remove all grease, dust, dirt or any other contaminants that may cause connection problems, and prevent any contaminants from spreading when cleaning the copper surface in the next step. Rinse the rest of the armature with a contact cleaner to remove any unwanted dirt or debris. Use only electronic contact cleaners, otherwise the insulation inside the armature may be damaged.
Next, we will reinstall the surface of the commutator to remove any pitting, traces left by the arc, embedded dirt, etc. Using only 600-mesh alumina sandpaper, tear off a part about the width of the commutator. Hold the armature with one hand, wrap sandpaper on the commutator, and press lightly to make the commutator rotate completely, not just back and forth. Not all armature shafts are the same size, so you may encounter problems with drill bits because some chucks cannot be opened large enough. Please prepare a piece of sandpaper with a suitable width and long enough to keep the commutator a few inches away. This allows for fairly uniform sanding, similar to using a lathe. Make sure to remove any surface defects. For sandpaper, any deep damage can be too great, so you need someone to recut the surface on the lathe.
Afterwards, clean the commutator with a contact cleaner, and use a plastic scribe to clean the distance between each rod to remove any debris generated before or after resurfacing. Next is to check the mica depth between each bar. For this armature, it is not necessary, but in some cases, the mica between the bars may be too high, causing the brushes to not be properly installed on the commutator. The mica should be about 1mm lower than the bar. This is also called mica undercutting. To cut back the mica, you can use special tools for this tool, such as cutting blades, files, but you can also use a razor.