The tip of a hacksaw blade can also be used effectively for the same purpose. In this case, the photo below shows using the tip of a metal blade from a reciprocating saw. Depending on the size of the gap, you can use a small blade and hand cut the grooves lengthwise. However, in this instance, the surface of the mica has also become essentially flush with the top of the bars. The carbon build-up on the copper surface is obvious, and it's also apparent that the commutator has been turned down several times over the many years.Īfter spending a few minutes on the lathe turning the commutator, it is much cleaner and smoother. Here is the commutator end of the rotor from a 1hp RI bullet motor. This process is called undercutting the mica. After turning the bars down, a user often needs to remove a small top layer of the mica to create that recess.
In order to ensure clean contact between carbon brush surfaces and the copper bars, the top surface of the mica should be slightly recessed below the surface of the commutator bars. The space between the copper bars on the commutator is a softer, non-conductive material called "mica". This is a fairly common procedure that only takes a few minutes with the rotor assembly mounted on a metal lathe. The first place to start when any repulsion-start/induction-run motor is having starting difficulties is to turn the commutator to eliminate any carbon build-up on the copper bars and to even out any imbalances or uneven surfaces. Turning the Commutator and Undercutting the Mica ¶ The approaches and tools shown in the original entry on this page were done in a hobbiest garage-shop, using moderate level tools such as a lathe, and do not require significant machinist skills or equipment. Fabricating and replacing the shorting necklace Turning the commutator and undercutting the mica
The page covers three major elements in troubleshooting and repairing internal components: This page shows some of the main internal components of a single-phase Unisaw repulsion-start/induction run (RI) "bullet" motor.
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