Trick for Fast Segment Cleaning of Commutator

I think any such tool would be substantially equivalent in action to the saw, and would take about the same time, which doesn't seem unreasonable in the first place.

There is a tool made and I think it's a Martindale cutter. But it's thirty years since I've seen one so don't take it as gospel! I've used one as an apprentice and as Tornado said it's no quicker.

Martindale also make a commutator stone to clean the commutator and a seating stone for bedding the brushes.

If needs be Morgonite can make brushes with a grinding insert in the brush face, but you need to look at their web site to see if they are suitable.

By the way the commutator has a nice patina on it, what do you think is causing the segment burring?

Based on the picture, my experience dictates that the cause of uneven commutator patina is overheating due to excessive arcing between the brushes and the commutator. This maybe due to the use of improper type of brush material and or wrong spring tension on some of the brushes. Partial shorts on some of the armature windings may also trigger too much arcing between brushes and commutator leading to commutator overheating..

"Friction between the segments and the brushes eventually causes wear to both surfaces. Carbon brushes, being made of a softer material, wear faster and may be designed to be replaced easily without dismantling the machine. Older copper brushes caused more wear to the commutator, causing deep grooving and notching of the surface over time. The commutator on small motors (say, less than a kilowatt rating) is not designed to be repaired through the life of the device. On large industrial equipment, the commutator may be re-surfaced with abrasives, or the rotor may be removed from the frame, mounted in a large metal lathe, and the commutator resurfaced by cutting it down to a smaller diameter. The largest of equipment can include a lathe turning attachment directly over the commutator."

http://en.wikipedia.org/wiki/Commutator_(electric)

http://www.morganamt.com/us/files/Morgan%20Carbon%20US/MaintenanceConcerns.pdf

The coarser the grit the heaver the burr. Try a fine grit to finish with. This will thin out the burr where it is attached. I usually deburr it with a curved xacto knife.

The most convenient method which I have used is to mount a small carbide disk cutter [ slitting style] of the appropriate thickness in the chuck of an electric die grinder. I use an 1/4" arbor and mount the disc on a shoulder on the end of this arbor. Normally i carry a selection of disks to suit various widths of commutator slots.

This grinder is mounted on the tool post of a lathe aligned with the commutator to cut the mica out of the slot, [This is done after the commutator has been skimmed and polished ]. The armature can be stepped round and the cutter run up for each slot, an indexing system can be mounted on the main spindle to assist in stepping but for a lot of smaller diameter commutators can be stepped by hand and eye.

After this procedure it will be necessary to bevel each slot this is done with a prepared hand tool of a suitable shape, then the commutator will need re-polishing.

To do your 150 slots about 2Hrs including set up.

Also,

I should have mentioned I use a speed control on the die grinder to get best result.

Also in reply to Andy soft mica might have suited some motors but in reality it leads to eccentric wear of the commutator more noticeable in high speed motors of which there are more nowadays,slots need cleaning out after skimming to remove trailing copper edges and undercutting due to new diameter. carbon build up in the slots is not a great problem usually a problem of overloading the motor which can cause segment lift.

Ah!

There was a time when the insulation between the segments was softer than the copper and it wore away in use and never needed undercutting....is that not the case anymore?

If the answer is negative, then motor manufacturers have taken a backward step......

The good point about such soft materials was that it prevented a buildup of carbon dust in the gaps between the segments. This can cause further sparking too.....

Too much commutator wear can sometimes be attributed to incorrect hardness of the brushes, only the manufacturer knows the hardness needed, the spring tension and the required angle to the applied fields.

The field angle plays a huge role with regard to wear and sparking, some motor brush holders are adjustable for angle, maybe this is part of the problem too.....

Its a good many years since I worked on big DC motors and generators, I am sure that some improvements must have been made in the last 50 years.....I would like to hear about them if possible....

Dear Friends;

At last I have found the required tool which is Black & Decker brand mini machine RT650. Please see the attached image.