How to Clean a DC Motor Commutator (Without Ruining Your Motor)

If you’ve ever opened a DC motor and seen a dark, streaky copper ring with black dust everywhere, that “ring” is your commutator asking for help. Cleaning it the wrong way can quietly shorten your motor’s life. Cleaning it the right way can make an old, noisy motor feel almost new again.

This guide walks you through how to clean a DC motor commutator step-by-step, but also why each step matters, so you’re not just following a checklist — you actually understand what’s going on inside the motor.

• What you’ll get from this guide:
  • How to tell when a DC commutator really needs cleaning (vs. when it needs repair).
  • The exact tools and chemicals that are safe — and the ones that will destroy your motor over time.
  • A practical cleaning procedure you can adapt for small tools and larger industrial DC motors.
  • How to look after carbon brushes and brush holders, not just the copper.
  • A simple way to decide: clean, refurbish, or replace?

1. Quick refresher: what the commutator actually does

In a DC motor, the commutator is the copper cylinder with segmented bars, sitting on the rotor shaft. Carbon brushes press against it and “switch” the current through the armature windings as the rotor turns. That switching is what keeps the motor spinning in one direction instead of just twitching.

Each brush is like a sliding electrical contact. It rides on a very thin film on the commutator surface, made of carbon and copper oxides. When that film is healthy, the motor runs smoothly with minimal sparking. When it’s dirty, uneven, or contaminated with oil, you get heat, noise, and eventually failure.

Over time, dust from the brushes, copper wear, moisture, and oil can build up. That buildup changes the contact resistance from bar to bar, and your motor starts complaining — first with small sparks and noise, then with heavy sparking, flat spots, and burnt bars.

• Common symptoms that dirt or film on the commutator is becoming a problem:
  • Visible dark streaks, burning, or banding on the copper bars.
  • Excess carbon dust packed around the commutator and brush holders.
  • More sparking than usual at the brushes (especially at light load).
  • Motor running hotter, noisier, or with fluctuating speed.
  • Power tools that “pulse” or lose torque under load.

2. How to tell if your DC motor commutator really needs cleaning

Not every brownish commutator needs aggressive cleaning. A smooth, even, chocolate-brown film can actually be healthy. The warning signs are change and unevenness.

A commutator probably needs cleaning when you see things like:

• Patchy, matte black deposits that don’t match the rest of the surface.
• Yellow, sticky residue or oil on the bars.
• Copper bars that look heavily streaked, with rough or raised spots.
• Deep, sharp grooves you can catch with a fingernail.
• Visible tracking or conductive dust packed between bars.

If you’re seeing heavy sparking, bar-edge burning, or flat spots, you may already have underlying problems like brush misalignment, wrong brush grade, or overload conditions that must be corrected alongside cleaning. 

• A good rule of thumb:
  • Clean only as much as needed to restore a smooth, even surface and good insulation between bars.
  • If you must remove a lot of copper to make it round again, that’s more refinishing/repair than “just cleaning.”
  • If multiple bars are burnt, loose, or cracked, skip cleaning and plan on professional repair or replacement.

3. Safety first (please don’t skip this part)

Commutators live in an awkward place: inside metal housings, surrounded by wiring, and sometimes connected to high DC voltages. Even a “small” DC motor can bite hard if you work on it live or let conductive dust go where it shouldn’t.

Before you reach for tools, disconnect and isolate the motor. For anything beyond tiny battery-powered motors, follow your facility’s lockout/tagout practices. Discharge any capacitors in drives, and verify no voltage is present.

Also think about the motor’s value and warranty. If it’s under warranty, or it’s a critical production motor, the safest path might be sending it to a service shop instead of experimenting with DIY abrasives.

• Minimum safety precautions you should treat as non-negotiable:
  • Disconnect and lock out power before opening anything.
  • Wear eye protection and a dust mask when dealing with carbon dust.
  • Use non-sparking tools and avoid loose jewelry or clothing near rotating parts.
  • Keep flammable solvents away from ignition sources.
  • Never spin the rotor with power applied while your hands or tools are near the commutator.

4. Tools and materials you should and shouldn’t use

Not all abrasives and cleaners are created equal. Some that are fine for metalwork are terrible for commutators.

Industry guides specifically warn that emery cloth with aluminum oxide is not recommended on commutators or slip rings, because conductive particles can embed in the surface and promote arcing.  Instead, they recommend non-metallic abrasives like garnet paper or dedicated commutator stones. 

• Safer choices for cleaning a DC motor commutator:
  • Vacuum or low-pressure compressed air For removing loose carbon dust (vacuum with a brush is often best).
  • Soft, lint-free cloths or clean shop wipes For dry wiping and solvent cleaning.
  • Isopropyl alcohol (IPA) or specialized electrical contact cleaner For removing oils/grease without leaving residue.
  • Garnet paper / non-metallic, fine abrasive sheets (e.g., 220–600 grit) Specifically made for commutators; avoids conductive grit embedding. 
  • Commutator stones or polishing sticks For light resurfacing where allowed by manufacturer.
  • Wooden picks / plastic sticks / fiber brushes For carefully cleaning between commutator bars (in the mica undercut).
  • Small tools: very high-grit wet/dry paper (800+), used sparingly For low-voltage hobby/hand tools only, and only when you clean all dust afterward. 

After you’ve gathered what you do want to use, make a short “ban list” for your shop: no emery cloth, no steel wool, no aggressive grinding wheels on commutators. Those might give a nice shine at first, but they tend to plant the seeds of future failures by embedding conductive or overly rough particles into the copper surface. 

For solvents, avoid anything oily or silicone-based (like generic penetrating oils) — they leave a film that attracts carbon dust and turns into sludge on the commutator.

5. Comparing commutator cleaning methods

Different motors and different levels of contamination call for different approaches. Here’s a quick comparison to help you pick the right one.

The golden rule is: start with the gentlest approach that might reasonably work, then step up in intensity only if the problem remains. Jumping straight to aggressive abrasives or machining for minor contamination is like using a chainsaw to sharpen a pencil.

6. Step-by-step: how to clean a DC motor commutator

Here’s a practical, adaptable procedure you can use for most DC motors (from hand tools to small industrial machines). For large, critical, or high-voltage motors, treat this as a conceptual guide and cross-check with the manufacturer’s manual before doing anything.

1. Isolate and open the motor
   • Disconnect all power and discharge any stored energy.
   • Remove covers or end bells so you can clearly see the commutator and brushes.
   • Take photos before you pull anything apart; they’re cheap insurance for reassembly.
2. Initial visual inspection
   • Look for loose or broken wires, burnt insulation, severely damaged bars, or cracked segments.
   • Check brush holders for packed dust, rust, or obvious misalignment. 
   • If bars are loose, cracked, or badly burnt, stop and plan for repair or replacement instead of cleaning.
3. Remove loose dust and debris
   • Use a vacuum with a small brush to remove carbon dust around the commutator and brushes.
   • If you must use air, keep pressure moderate and blow dust away from windings and bearings.
   • Don’t grind dust deeper into crevices — vacuum first, wipe later.
4. Clean the brush holders and brushes
   • Carefully remove the brushes, keeping track of their position and orientation.
   • Wipe the brush holders with a cloth lightly dampened with IPA or approved cleaner.
   • Check each brush for uneven wear, chips, or cracks; replace brushes worn beyond about 50% of their original length or as per OEM specs. 
5. Solvent-clean the commutator surface
   • Dampen a lint-free cloth with IPA/contact cleaner (don’t soak it).
   • Rotate the rotor by hand while gently pressing the cloth against the commutator.
   • Wipe until the cloth comes away much cleaner; replace cloth sections as they get dirty.
   • Let everything dry completely.
6. Light abrasive cleaning (if needed)
   • If the surface is still rough or has light streaking, use garnet or non-metallic fine abrasive.
   • Wrap a strip snugly around the commutator, abrasive side inward, and apply light, even pressure while rotating the rotor in its normal direction.
   • Your goal is not to re-machine the commutator — just to remove glaze and small high spots.
   • Afterward, vacuum and wipe again to remove all abrasive dust.
7. Clean between commutator bars (the mica undercut)
   • Use a wooden or plastic pick, or a stiff fiber brush, to gently clean any conductive dust from the grooves between bars.
   • Do not aggressively deepen the undercut unless you know the OEM spec; you only want to remove contamination.
   • Vacuum as you go so debris doesn’t migrate back onto the surface.
8. Final wipe and visual check
   • Give the commutator a last wipe with a clean, solvent-damp cloth.
   • Inspect under good light: the surface should be smooth, with no burrs, raised edges, or significant grooves.
   • Check again that there’s no debris bridging between bars.
9. Reinstall and seat the brushes
   • Reinstall new or cleaned brushes in their original positions.
   • If recommended, seat new brushes with garnet commutator paper pulled in the direction of rotation so that at least ~75–80% of the brush face contacts the commutator. 
   • Vacuum away any seating dust afterwards.
10. Test run and monitor
    • Reassemble the motor and run it at no-load initially if possible.
    • Listen for unusual noise, and watch sparking at the brushes — a small, even “halo” is normal; heavy bright sparking or bar-edge arcing is not.
    • After a short run, stop and recheck for loose dust and abnormal heating.

For small, low-cost tools (like hand drills or hobby motors), you can simplify: clean dust, solvent-wipe, very light fine abrasive if absolutely needed, then reassemble. For large or critical DC motors, steps like checking brush spring pressure, brush neutral, and air gap should be part of the process, following standards such as EASA AR100 and the OEM’s manual. 

7. Deep cleaning and light resurfacing (when simple wiping isn’t enough)

Sometimes you open a motor and immediately know: this isn’t just a “wipe and go” situation. Maybe there are light flats, minor eccentricity, or stubborn burn marks that outlast normal cleaning.

In those cases, light resurfacing can help — but it must be done with restraint.

• Options when basic cleaning doesn’t restore a smooth, healthy surface:
  • Commutator stone “touch-up” in place Good for minor surface roughness, when you can safely rotate the motor (often at low speed) and apply the stone under controlled pressure.
  • More aggressive abrasive with careful control Only under manufacturer guidance, and using proper non-metallic abrasives designed for commutators.
  • Ultrasonic cleaning of a removed rotor Useful where commutators run in dirty, oily environments and can be removed to a tank for deep cleaning.
  • Turning and undercutting in a shop When the commutator is badly worn, egg-shaped, or heavily burnt, a motor repair shop can turn it in a lathe and re-undercut the mica to like-new condition.

If you’re unsure whether you’re still “cleaning” or you’ve crossed into “machining,” that’s a strong sign to consult a motor repair shop. Removing too much copper in the name of “getting it perfect” is a classic way to dramatically shorten commutator life.

8. Don’t forget the brushes and brush holders

A clean commutator with bad brushes is like new tires on a car with broken suspension. A huge amount of commutator damage comes from brush and brush-holder issues, not just dirt.

Industry recommendations emphasize: brushes should fit properly in the holders, move freely, have the correct spring force, and be of the proper grade and size for the application. 

• Brush & holder care checklist:
  • Clean the holders so brushes can move freely without sticking.
  • Check spring tension and replace weak or uneven springs.
  • Use consistent brush grade across brushes in the same circuit, unless the OEM specifically says otherwise.
  • Seat new brushes properly with garnet paper or equivalent, then vacuum the dust.
  • Inspect brush faces for abnormal wear patterns (chipping, streaking, diagonal wear) that hint at misalignment or vibration.
  • Confirm brush position (brush neutral) where required for DC machines, following the OEM procedure.

If you keep having to clean the commutator frequently, step back and ask: are the brushes right? Wrong grade, poor seating, or misaligned holders can keep damaging the commutator faster than you can clean it. Fix those, and cleaning becomes an occasional tune-up instead of a weekly chore.

9. Mistakes that quietly destroy DC motor commutators

It’s worth calling out the most common ways well-meaning people unintentionally damage commutators while “maintaining” them. Many of these look fine the day you do them — and then the motor comes back with worse problems months later.

• Things to avoid at all costs:
  • Using emery cloth or metallic abrasives that leave conductive particles embedded in the copper. 
  • Aggressively sanding in one spot, creating flats or taper instead of a true round surface.
  • Leaving abrasive or carbon dust inside the motor after cleaning.
  • Using oily or silicone sprays on the commutator or brushes.
  • Ignoring heavy sparking or burning after cleaning, instead of tracking down the root cause.
  • Mixing brush grades randomly, which can destroy the commutator film and cause uneven loading.

A helpful mindset is: you’re not polishing a decorative part — you’re tuning an electrical interface. Smoothness, cleanliness, and correct electrical contact matter more than mirror shine.

10. How often should you clean a DC motor commutator?

There’s no one answer that fits every motor. Cleaning needs depend on:

• Load profile (light duty vs. near full load, continuous vs. intermittent).
• Environment (clean, dry panel vs. dusty or oily atmosphere).
• Brush grade and quality.
• How critical the application is (cheap drill vs. production line motor).

That said, you can sketch a rough starting point and then adjust based on what you see during inspections.

• Example starting points for inspection & cleaning intervals:
  • Small hand tools & hobby motors: Inspect every 6–12 months or after heavy projects; clean when sparking or visible dirt increases.
  • General-purpose DC motors in clean environments: Inspect every 2,000–4,000 operating hours; light cleaning as needed.
  • Harsh or dusty environments (mining, cement, woodworking): Inspect more frequently (e.g., every 500–1,000 hours), with routine dust removal and occasional solvent cleaning.
  • Critical industrial drives: Follow OEM and site maintenance plans — often with scheduled shutdown inspections, brush measurements, and documented commutator condition.

Use these as starting guesses, then tune your schedule after you’ve seen your motors over a full cycle of seasons and production loads. Your own logs and photos will beat any generic rule of thumb.

11. When cleaning is no longer enough

Cleaning can’t fix everything. Some commutators are simply at the end of their useful life, or have suffered damage that goes beyond contamination.

• Signs that you should stop cleaning and plan for repair or replacement:
  • Multiple bars are burnt, cracked, or loose.
  • The commutator is visibly out-of-round, and you can feel significant steps or flats.
  • Deep grooves are present that would require heavy material removal to eliminate.
  • Even after proper cleaning, sparking remains heavy and concentrated in specific zones.
  • Insulation between bars (mica or resin) is breaking down, missing, or smeared across the surface.

At that point, the question becomes economic: Is it cheaper and more reliable to send the rotor to a motor shop for turning and undercutting, or to replace the motor outright? For many small tools, replacement wins. For larger DC machines, professional refurbishment often makes more sense than running on a damaged commutator until a catastrophic failure.

12. Quick FAQ

• Can I just “shine it up” with any fine sandpaper? Use non-metallic, non-conductive abrasives like garnet paper or dedicated commutator paper, not emery cloth or random metal-bearing sandpapers. 
• Is a dark commutator always bad? No. A smooth, even dark brown film is often a sign of a healthy brush/commutator interface. Patchy, burnt, or heavily streaked areas are the real red flags.
• Do I have to replace the brushes every time I clean? Not necessarily. But if they’re worn near their limit, chipped, cracked, or seating poorly, it’s smart to replace them during a cleaning shutdown.
• What about spraying contact cleaner while the motor is running? Don’t. You risk fire, insulation damage, and driving loosened debris into places it shouldn’t go.
• Can I fix sparking just by cleaning? Sometimes. But persistent heavy sparking often points to deeper issues: wrong brush grade, misaligned holders, overload, or winding problems. Cleaning is step one, not the whole story.

13. Closing: making your DC motor boringly reliable

A clean DC motor commutator doesn’t look impressive — it looks boring: smooth, evenly colored, no drama, no flames. That’s exactly what you want.

If you:

• Keep dust under control,
• Use the right abrasives and solvents,
• Treat brush and brush-holder maintenance as part of cleaning, and
• Know when to hand off to a repair shop,

your DC motors will quietly do their job for years with fewer surprises and less downtime.

You can absolutely clean a DC motor commutator yourself — safely and effectively — as long as you respect what that copper cylinder is doing and work with it, not against it.