Large grooves in PMDC brushes-brand new...

MICHAEL11573

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Has anyone ever seen groove like these on brushes on a brand new permanent magnet DC motor? I bought a MX-210V, 8 x 16 lathe and the howling coming from the motor is unbearable, it's definately coming from the brush end of the motor, so I pulled the brushes and this is what I found. Not sure but every brush I've ever changed in a drill or what have you, have always been smooth.....I googled around and didn't see anything like this.....thanks all in advance
 

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stupoty

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I've seen a lot of brand new brushes like that (on different kinds of motor) , I think it's so they bed in quickly.

Others may have seen the same thing.

Stuart
 

jbobb1

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Never seen new brushes like that. Seems like a bad idea to me.
 

Flyinfool

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That is a very common feature on replacement carbon brushes. As mentioned above it dramatically reduces the amount of time it takes to seat the brushes to the commutator. Where I work all replacement carbon has those grooves.
Running a motor at full power before the brushes are seated can burn up the commutator due to insufficient contact patch. Let it run for a bit with no load if possible to get the brushes seated good.

A howling motor is usually bearings.
 

MICHAEL11573

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Thanks for the tip on the full power before wear in Flyinfool, and everyone else....I couldn't find any info about it so I ended up shaping them smooth with a slight contour...the high pitch wasn't as bad afterwards, also ditched the DC speed controller that came with the lathe, and grabbed a different one out of my small collection of kbic's.....the difference was night and day....no more high frequency squeal, there was no way in hell I could deal with that squeal after all the weeks of working to get this lathe to where it should be, I figured spending a thousand dollars on something you should be able to use it on arrival, unlike the $4-500 variety but I was wrong.....the biggest thing about these lathes is the cleaning, I bet I had 2 weeks into cleaning the dirt and milling dust, gravel, wood, shavings, filings you name it, it was in the crate, but anyway lol thanks again guys, when I get her finished I'll be back for turning tips, and such as I am just starting out, and I can tell all you guys know your **** I was reading some of your stuff so cool take care
 

markba633csi

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The KB controller you installed will be more reliable than the stock one- good choice
 

Downunder Bob

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Many years ago when the ships I worked on were DC 110V as I recall. the big motors had some pretty big brushes. When fitting new brushes to a motor we'd place a strip of fine sandpaper between the brushes and commutator and turning it we could shape the brushes to fit the commutator and by the time the motor was run up to speed the brushes would be pretty well bedded in.
 

Flyinfool

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Another tip for your carbon brushes.
If or when you remove them for inspection, like to see if the wear patter is across the full face, you must put them back in the same holder and in the same orientation. If you put them in different they will have to reseat due to manufacturing tolerances having them not exactly in the same spot relative to the com. It is not a lot, but if you turn a brush around and run the motor for a couple minutes and pull the brush back out you will be able to see that only a very narrow area is actually making contact with the com.
Any time you are running the motor with less than full contact the amps per sq in go way up and you are stressing and heating the armature, it will not show up right away, but it will reduce ultimate service life.
We once tested some motors. Run at full load with proper breaking of the carbon vs run like a customer would by just slapping in new brushes and going back to work with no break in time. On average the motors that had proper carbon break in had an ultimate service life that was about 15% longer.

There is a lot more science in carbon brushes than most people realize.
 

Joeman77

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Brushes are nice & quiet, maybe some arcing noise during run-in but, no howling! Sounds like you've got bad bearing in that end, right out of the box, it happens and more often than anyone wants to admit, check that too.
 

MICHAEL11573

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What does the commutator look like?
The commutator and the brushes are brand new that came in the lathe's permanent magnet motor, I've had this lathe 2 months now and this is the first time fired up and the squealing pitch it was emitting was unbearable to any human, I would rather place my head in a microwave oven than have to hear that again....lol
Many years ago when the ships I worked on were DC 110V as I recall. the big motors had some pretty big brushes. When fitting new brushes to a motor we'd place a strip of fine sandpaper between the brushes and commutator and turning it we could shape the brushes to fit the commutator and by the time the motor was run up to speed the brushes would be pretty well bedded in.
Excellent idea to get the exact contour, thank you Downunder Bob!!
 

MICHAEL11573

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Another tip for your carbon brushes.
If or when you remove them for inspection, like to see if the wear patter is across the full face, you must put them back in the same holder and in the same orientation. If you put them in different they will have to reseat due to manufacturing tolerances having them not exactly in the same spot relative to the com. It is not a lot, but if you turn a brush around and run the motor for a couple minutes and pull the brush back out you will be able to see that only a very narrow area is actually making contact with the com.
Any time you are running the motor with less than full contact the amps per sq in go way up and you are stressing and heating the armature, it will not show up right away, but it will reduce ultimate service life.
We once tested some motors. Run at full load with proper breaking of the carbon vs run like a customer would by just slapping in new brushes and going back to work with no break in time. On average the motors that had proper carbon break in had an ultimate service life that was about 15% longer.

There is a lot more science in carbon brushes than most people realize.
Yep I marked the proper orientation when pulling them with a sharpie, thank you very interesting stuff
 

MICHAEL11573

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Brushes are nice & quiet, maybe some arcing noise during run-in but, no howling! Sounds like you've got bad bearing in that end, right out of the box, it happens and more often than anyone wants to admit, check that too.
Bearings are fine, right when I got the lathe in the mail I started a complete tear down, they are the tapered roller bearings, not NSK or any big name they are a china made but with surprising good quality, thank you
 

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MICHAEL11573

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The KB controller you installed will be more reliable than the stock one- good choice
This is the one it shipped with, IC next to the bridge rectifier is a IGBT, main chip is a Holtek, I believe they tried to cram way too much onto the small board and that is where I believe is the root cause of all the noise that appeared on the motor....thanks
 

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markba633csi

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Looks like a high frequency drive, they have a reputation and it's not the best
They skimp on the output devices and the protection circuitry
www.olduhfguy.com
 
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