Picture of Rebuiding A DC Motor Commutator
So you have an old, hard to replace DC motor, and the commutator is worn completely through?  It happens to the best of them, and in this case, the motor has been in daily use for over twenty years!
  Unfortunately, I do not have a 'before' picture, but I have taken shots of the repair process.

The first picture here is the final result.

Kind of a tease, no?
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Step 1: Rebuiding A DC Motor Commutator: Clean up the Commutator Shaft

Picture of Rebuiding A DC Motor Commutator: Clean up the Commutator Shaft
To clean up the old shaft, it was necessary to turn the nasty bits down in a lathe.

I secured the output shaft end in the lathe-chuck, and to ensure true turning, I places the commutator end of the shaft in a bushing held in the tail-stock chuck.

It took some very careful cutting, but I was able to remove very little of the insulating core material, which appeared to be phenolic.

Note that the 'lugs' on the left of the phenolic are the wiring attachment points, and the 'ring of dots' on the right are the sad remains of the commutator sectors.   In most commutators, the sectors are molded into the core, with tabs or under-cuts.  The 'beads' on the right are well embedded into the phenolic core.

The 'lugs' are beveled to help with soldering adhesion of the new sectors.

BTW, the phenolic diameter is just under 1/2"! (1.2 cm)

Step 2: Rebuiding A DC Motor Commutator: The new Commutator Sectors!

Picture of Rebuiding A DC Motor Commutator: The new Commutator Sectors!
Here we see the new sectors, that is if you squint real hard!

The copper ring was selected to have a very close fit (almost press-fit!) to the phenolic core.
The ring was cut from a copper-pipe reducer, intended to receive a 1/2" nominal Cu pipe.

Note the bevel inside of the copper ring.  It is a soldering thing!

Step 3: Rebuiding A DC Motor Commutator: Test-fit of new sectors...

Picture of Rebuiding A DC Motor Commutator: Test-fit of new sectors...
Yes, that is a snug fit!

Step 4: Rebuiding A DC Motor Commutator: Prepation for Soldering....

Picture of Rebuiding A DC Motor Commutator: Prepation for Soldering....
Here we see the lugs, the 'beads' and the inside of the copper rings have all been tinned with solder.

Note on the solder!

Lead free, high-melting point stuff. 

Stronger than tin-lead, by a bit.

After tinning, I used solder-wick to remove excess solder, as too much would not allow parts to fit properly.

Step 5: Rebuiding A DC Motor Commutator: Soldering!

Picture of Rebuiding A DC Motor Commutator: Soldering!
Here we have the copper ring securely soldered into place.  Not evident is the sweat-soldering of the 'beads' on the right end of the core.  Trust me, they are soldered!

Use -lots- of non-corrosive paste flux!  This will help prevent solder bridging at the lugs.

Step 6: Rebuiding A DC Motor Commutator: Truing up the ring...

Picture of Rebuiding A DC Motor Commutator: Truing up the ring...
OK, so the thing goes back into the lathe as before, and -very- small bit of material is removed from the copper ring.

Then a bit of Scotch-Brite red for a nice finish.

Also turned down the right end of the ring, to expose just the edge of the 'beads'.  See, told you they were soldered!

Step 7: Rebuiding A DC Motor Commutator: Slotting.

Picture of Rebuiding A DC Motor Commutator: Slotting.
OK, this part I hated.  First used a Dremel style circular saw blade.  Heated up fast, melted solder, sectors went flying. Harsh language, tears ensued.
Ended up using Xacto-style razor-saw.  Slow, tedious, but accurate cuts.

After cutting, drizzled in some cyanoacrylate cement, which wicked under the sectors.

Solder should hold them, gluing can't hurt.

Back on the lathe to de-burr the sector edges, and job is done!

Big NOTE:  This motor is being used as a light-duty servo.  Any high RPM or heavy current applications should use hard silver-solder or brazing instead of electrical solder.  The phenolic core can tolerate brief high-heat.

Step 8:

sconner11 year ago

Nice work. I agree about using glue. Solder is not a good mechanical connection, especially under any stresses.

On a side note: What made you decide to rebuild as opposed to ordering a suitable replacement motor from an industrial supplier? Overall cost (labor time vs. new)? Shipping time? Braggig rights? Richly deserved, by the way.

teo.sinclair10 months ago

First time getting down to a DC motor; could not find a replacement for the original, and a shot commutator was holding up an important project. Nobody local could help, but you know what they say about necessity... so yes, I'm a novice, but I found this pure genius, followed the instructions, and it worked like a dream. I didn't have a lathe, but a steady hand and my power drill tightened into my Black&Decker workmate and the armature tightened into the drill worked perfectly. I used the same workmate to hold the armature while I sawed out the slots and I was amazed at how quickly that went... 12 slots in about 45 minutes. A very small triangular file gave a smooth, very slightly bevelled finish to the cuts. Crazy glue is a good tip, too, both before and after cutting, polished up after dry with a little steel wool then air-blown clean. Huge thanks for a great improv as well as photos and instructions that didn't take me halfway there!

dmoeller11 year ago

Great writeup. Just another reason for me to get myself a lathe.

nate711732 years ago
Awesome! Brilliant!
MTtoo3 years ago
I have in my box of seldom used lathe tools, a tool post grinder attachment. Fits in the toolpost holder just like a cutting bit holder. The other end has a round hole to fit the air operated grinder. A small burring grinder with a 1/4 chuck. Put a Dremel cutter blade in the burring grinder and control the communtator cut with the tool post feeds.
I have not done an operation like the communtator replacement, but I am thinking that the lathe could be put on a low speed and the copper "ring" heated with a small torch as it is turned. When it is close to soldering temp use the electric soldering gun to catch each segment as it is sitting on top. Lathe stopped naturally.
Horsehockey3 years ago
Someplace on Instructables I saw one to make an Induction Heater. Seems like that would heat the entire copper ring to soldering temps in a hurry. I do know that a bearing heater will provide a high heat and it is an induction heater but commercially made.
I have been around a long time and have been exposed to many tricks, but without a doubt this one takes the cake!!
Always wondered how the communtator was made, and if it was possible to repair. Your outstanding pictures and clear comments made your repair very understandable.
Thanks for your time and skills.
pirobot668 (author) 3 years ago
Sorry, sorta got out of sequence. I used a soldering iron to tin each of the lugs individually, then used Solder-wick to minimize the residual solder. Did the same for the 'buttons' on the right end. I also tinned the inside edges of the copper-ring, using the same apply/remove technique. This is essential due to the close mechanical fit of the parts. Too much solder, it don't fit!
Once it was all tinned, I reassembled the ring onto the shaft, then used a hot-air paint-stripper to heat up the ring and all the lugs at once. Once it was all hot, I used the soldering iron to help direct the flow of some additional solder. The iron just couldn't heat up all that copper, so the heat-gun got all the parts close to the solder melt temperature. The soldering iron really did the work.
gourdhedd3 years ago
What did you use for heat to solder with? Large soldering iron? Propane?

pirobot668 (author)  gourdhedd3 years ago
Soldering heat was supplied by a Weller Hot-Air paint stripper! Set the sucker to high, had some construction paper wrapped around the armature to protect the wires. Since all the surfaces requiring solder were well tinned, the heat just re-flowed the solder. Did a little touch-up with a soldering iron when all was still hot.
please help me !!!
The best way I ever found for recutting the slots is a "planing" cutter mounted in the toolpost, and used to scrape the slots.
lord_kian3 years ago
this is a usefully guide to a critical fix when you do not have a spare motor to replace.
i hope that you win something for this
profpat3 years ago
nice one, but needed to borrow a lathe, hope we have a diy lathe for this!
pirobot668 (author)  profpat3 years ago
One could use a power-drill, clamped to a sturdy table as the lathe head, some sort of blocky/clampy affair to hold the bushing at the far end of the shaft, and a Dremel tool to do the cutting/truing on the commutator surface.
Mount the Dremel in a v-block, some yard-stick material making a channel for the Dremel to move parallel to the axis of the motor shaft.
Tricky, tedious, but quite likely to work well if one is patient.
ilpug profpat3 years ago
You can improvise by putting the spindle in an electric drill and spinning it against a file.
alterator3 years ago
just attempted to do this a couple of weeks ago. everything the same as you did, until the part where you put a tube around the axis. I tried to solder each prepared piece seperately by gas torch. first one was a success, but didn't have patience to finish the rest 11 pieces. :D

nice work, and idea.

mr fat3 years ago
This is one fantasic guide thank you for showing us!
torino66693 years ago
Totally COOL!!
It's nice to see people still doing things like this. My Pop's showed me how to do this when I was a teenager & needed to fix the starter on my old car ('69 Torino Ragtop, of which I still have) (SMILING) with little money. I will have to show him this structable. This is an awsome trick & a very good Structable. All Hail the Repairers, Tinkerers & Repurposers of the World!! LOL (HUGE GRIN) BTW, Thank you for the fond memories I recalled working with my Dad back then. It's actually something I still do on a regular basis. (GRIN)
I also agree with rimar2000, you deserve a Patch. Now if I could just figure out how to give you one, Hmmm....... I'll send this so I don't lose it the figure out how to give a patch. Back soon (GRIN)
pirobot668 (author) 3 years ago
Thanks for the tip! Woulda, coulda, shoulda. Using the Dremel blade did result in two segments having to be re-soldered. :(
In a starter, since the current is much higher, hard solder or brazing would work better. Phenolic core is tolerant of brief high-heat.
This repair was a one time deal; needed the repair right now, and since the motor was so old, a replacement could not be found.
BTW, thanks to Western Electric for the training that I got back in the early eighties. They taught me all kinds of repair/rebuild skills.
How does this differ from the "official" repair procedure (If any?)

I've actually never seen one repaired. Some auto repair manuals show tear-down and replacement of internal starter or alternator parts, but I recall them saying if it's gone, its gone.
pirobot668 (author)  kill-a-watt3 years ago
Depending on the original construction of the commutator, there may not be a whole lot left.
The 'official' way is to replace the entire commutator body, which requires some wire cutting/soldering.
One technique is to use micro oxy/acetylene torch to weld new sectors onto the lugs.
Might burn the commutator hub, but does a fine job.

Since there is so much variation in how they are built, done is sometimes done, get a new core.
rimar20003 years ago
Excellent refurbish work, you deserve a patch!
omnibot3 years ago
Nice job.
How about precutting with the dremel before soldering to make the job easier.
ironsmiter3 years ago
That is AWESOME!
Now i wish i hadn't recycled the truck's starter, with the melted commutator(3 of 12 of the sections were completely severed, the rest damaged).
This little trick could have saved me over $100.
Now I'll know for next time!

If you do it again, try a thin slitting saw blade, on an arbor, mounted in the lathe chuck/headstock.

build a jig to clamp the shaft to the cross slide.
   can be as simple as a v-notch cut in a block of wood.
   for something a little more secure, and complicated, a block of wood, drilled slightly oversized compared to the lamination section diameter. then clamped tight using a nut and bolt.
    If it's gonna be a regular thing, repairing various commutators, I'd be very tempted to build something like this to mount to the crossslide.

Either way, place your slitting saw on backwards, and run the lathe in reverse, at slow rpm's. ok, slow compared to your dremel! :-) probably under 1000RPM should still work fine. Slower is better, since you have a tentative grip on the piece, but it's also a VERY light cut, so not too much worry.
Using the crossfeed handle, you should be able to slowly advance in toward the sawblade. Just like on a table saw, stay out of directly behind it. It probably won't but CAN catch, and throw that sucker straight back into you, if you happen to be standing in the right spot. Even with the lather at 60RPM, it'll leave a bruise if the work piece hits you.