Turning down small motor commutator question
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  1. #1
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    Default Turning down small motor commutator question

    A while back I had a small drill press motor that was acting up, see details below from an earlier post. This drill press I had bought years ago on ebay as a spare and never ran it. After checking things and cleaning it and I realized the motor's trust washers were put in wrong and the brushes were not in good contact with the commutator which was also worn uneven. So I turned it down, took off maybe about .005 to .010" and then cleaned out the spaces between with a graver. Removed any burrs with a #6 cut file and burnished them a bit. Also filed the ends of the brushes to the correct profile. It now runs much better but sometimes it still sparks way too much and the speed is not consistent. Most of the time it feels like it is running slow.

    What could cause this? When I cut the slots in the commutator I was worried I would cut too deep, does this sound like some could be shorting out? Was burning a bad idea? I read somewhere it said do not use sand paper on a commutator.

    The wiring looks good, the motor is not heating up, the belt tension is fine as are the bearings. I have a 3 of these on a bench and have been using the for decades so I know how to adjust them at their sweet spot.

    Thanks,

    Here is the original post.

    "I have a bunch of Cameron Drill presses, These were made in CA. starting in the 1960s and stayed nearly unchanged for 50 years. The motors they originally used were built for them and I understand they have run out of them and the parts. They were a 110 volt motor with brushes kind of like a sewing machine motor. I have one that when I take it apart everything looks fine but when I turn it on it starts off slow and blows a lot of smoke out of it and then it seems to run smooth and at speed after a minute or so. It also stops blowing smoke. I do not think there is too much tension on the belt or any other source of resistance in the spindle or motor bearings."
    Attached Thumbnails Attached Thumbnails dscn2327.jpg  

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    Brushes not being pushed in to the armature hard enough ????

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    Did you grawl the arm for a short?...Phil

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    Smoking etc may also be oily brushes.

    I have a drill-driver that sometimes sparks and smokes a bit when it starts, usually after sitting a longish time. Commutator was also really dirty when I used it at first. It was new, and just not used much, I had bought it to get 2 spare batteries (cheaper than the batteries alone!) . That one's problem was oil, I cleaned it out and it has mostly stopped.

    If one or more segments has lost the connection to the coils, you can get "ring fire", sparks that seem to go circling around with the commutator.

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    You need to use sandpaper (with the commutator to guide you) and sand the brushes to the same radius as the commutator.

    Read here. https://www.pdma.com/pdfs/tips/2008/1_02_08.pdf

    I was told by an old time motor man that you undercut on generators but not on motors.

    I can't find anything on the internet to conform this. However I have followed his instructions on a few motors and they turned out fine.

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    This may be the problem,
    When cutting commutators on a lathe, it is best to not use the shaft center to hold the end true. The shaft centers are there for winding the armature, not centering the commutator.
    Old machines like SB, and Atlas among others, provided commutator chucks, the tailstock chuck has brass jaws, the shaft rotates in the brass instead of the shaft center that may not be concentric with the commutator.
    When the commutator is not concentric with the bearing surface of the shaft, the brushes dance and spark.
    If you dont have a jacobs commutator chuck, you put a fitted brass bushing in a drill chuck, or collet chuck, having the shaft rotate in a bearing, instead of using a tail center.
    Information like this is nearly lost because small shops dont do generator, and starter repair anymore.
    How do I know this? Harley Davidson factory trained, of course!

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    Not an expert...

    It may be sparking as the corner of the commutator contact comes off the brush creating an arc gap.

    Someone above mentioned not cutting motors.

    Suggestions.

    With very thin and fine sandpaper place it between brush and commutator to match the two more closely.

    Two options, experts can comment...

    Epoxy fill spaces between the bars.

    Difficult but possible, use lathe to get close then file after cure.

    Or round over the corners to remove the sharp corner.

    Good luck!

    Sent from my SAMSUNG-SM-G930A using Tapatalk

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    There is another option, Slip Ring and Commutator dressing stones.
    These are used by the pros in the field for dressing commutators on "running motors". Also used by vacuum cleaner repair techs on tiny motors.
    If you can glue a piece of stone to a stick, and get it in there, you could correct your problem.
    The stones are sold by Ideal Electric, these stones actually get the commutators perfect if they can be applied.
    That information is on the instruction panel on early Monarch 10ee lathes that have the motor generator, there are 3 commutators on the machine, dressing them with the machine running is dangerous to say the least.
    I dont make this stuff up, research it and be careful with powered up motors!

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    Freaky duplicate post thing happened, I will mention, I fixed a really old Ball half inch drill with a dressing stone, with out taking it apart, it was still running but sparking badly.
    The brushes, form in at the same time,
    And one more thing comes to, mind, sometimes the commutator bars will drift out ward causing sparking, probably means they are coming loose. Usually the armature works good for a while, then gets bad again.

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    I've found from working with hundreds of small brushed motors is that there will be extra sparking initially until the brushes bed in. It's difficult to get brushes to contact properly at first, even if you take note of which brush went into which side and in which of two orientations so there four possible combinations. You'll need to run it for several hours to re-bed randomly fitted brushes. Also new bearings will run noticeably warmer until the grease gets settled into position after a few hours operation.

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    Thanks everyone, I think run it a while and see if it improves, if not take it apart and look closely for issues.

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    Good advice above. I'll just add that it might be worth checking for a brush position adjustment. Not common on universal motors, but very common on repulsion motors.

    Repulsion motors with brushes set too close to hard neutral will draw lots of current, hum/buzz, start slowly, produce little torque and throw sparks. Easy to tell what you have by the presence of short-circuited brushes.

    Figured I'd mention the possibility as the cloth-lashed windings would seem to suggest it might be from that era.

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    I recently did the same with our Blentec blender. First I covered the comm with self-adhesive sandpaper, assembled and turned it until the brushes looked good. Then colleted the armature in the lathe, with a live center in the TS, confirmed the comm was running true within a few tenths, and turned it with a nice sharp tool. Cleaned out the chips, lightly sanded the comm and beveled the edges of the brushes so they wouldn't catch, and assembled. It did spark a lot for a few cycles and shed a lot more black brush dust but settled down afterward. Unfortunately, I waited too long to fix it and lost a winding, but at least it worked for a few weeks until we got a new blender.

    I did the same to a starter motor in my old Honda, but I had to replace the brushes as they were worn out. It was still working fine 140,000 miles later when I sold the car.

    I would run it without a load for a while to seat the brushes.

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    This document explains why using stones on running at speed commutators is the best way, and perhaps the only way to do this particular job right.
    This is one of those black arts things, where its dangerous, and only those most experienced electricians or millwrights do this on running equipment in plants, and vacuum repair techs also use the stones, available mounted on sticks.
    It seems Ideal Electric never had much online with this product, but my local industrial electric supply has their catalog, and also directed me to a user of the product to help me get going repairing the motor generator in an early Monarch ee lathe, No one here knew anything about the process 18 years ago.
    Some basics here.

    http://www.lfc554.ru/download/be16gb/ae1616gb.pdf

    Probably, the easiest way to get a stone is on ebay, and generally medium grade will work fine.
    You can cut the stones with an old hacksaw blade and glue them to sticks, to access the commutator. The stones are very soft, and conform to the commutator quickly, its similar to honing, moving the stone back and forth.

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    Again thank you for all your help. Here is an update. Today I ran this for an hour with no load (belt removed), after a while it would pick up some speed. At first it sparked like before but in time that stopped by about 60%. It still throws a little more spark than the others. It ran very cool, almost cooler than when I started it, must have a really good fan. Put the belt back on and it ran ok, much better than before but not as smooth as with no load. The spindle and bearings seems fine, feels just like the others. It often sparks a little at first and sometimes while running it pops, sort of a big spark. Sometimes when I go to turn it on it plays dead, nothing happens. If I turn the shaft to a different position it runs.

    So does this mean it has a dead winding? Or shorted? Is there a fix? Could it be a commutator problem? I did not want to take it all apart for fear of messing up the alignment of the brushes. Or can I take it apart and just make sure they are put back as the were? What should I be looking for?

    Again, thanks.

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    Quote Originally Posted by rivett608 View Post
    Sometimes when I go to turn it on it plays dead, nothing happens. If I turn the shaft to a different position it runs.
    Ohm the rotor windings between each commutator pair. Not starting and no humming means no current is flowing. Bad winding or bad brush contact would be my guess.

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    I know this will sound stupid, but how is commutator paired? Are they opposite? Every so many spaces? Next to each other?

    The last time I thought much about how motors worked was when I made one in 7th grade shop class. That was a while back.


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