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  1. #16
    Join Date
    Oct 2015
    Location
    melbourne
    Posts
    420

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    The lms ones are close, but with shipping and conversion to aud, comes in at nearly $40.
    I spoke to a lovely lady at Schunk in Melbourne who have a good range, she identified some i could probably modify ok. ($25)Or they can also custom manufacture, but @ $40 (plus tax) (each) i will keep looking for candidates to modify.

    I have found in my stash an old ducted vacuum motor with brushes just about wide enough i should be able to file down.

    (ive also been looking at various other devices; it seems to me that often they are installed in a metal tube which would also serve to connect the brush in addition to the spring)

  2. #17
    Join Date
    Mar 2011
    Location
    Adelaide
    Posts
    894

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    Quote Originally Posted by Sparksy View Post
    Most large DC motors use that method. easy to change as just pull back the spring , remove old brush and pop in new one. Only small dc and ac motors use pigtails and coil springs.
    To go off on a tangent for a moment..
    The DC fuelled locomotives at work have a length of 1 1/4” x1/4” copper braid connecting them to the primary traction bus, using 5/8 bolts torqued to some ridiculous level that requires the use of a hydraulic nut spinner. The brushes themselves are about 4”x2” and there are several brushes common to each other around the perimeter.

    Back to scheduled program

  3. #18
    Join Date
    Apr 2018
    Location
    Perth
    Posts
    100

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    Quote Originally Posted by racingtadpole View Post
    To go off on a tangent for a moment..
    The DC fuelled locomotives at work have a length of 1 1/4” x1/4” copper braid connecting them to the primary traction bus, using 5/8 bolts torqued to some ridiculous level that requires the use of a hydraulic nut spinner. The brushes themselves are about 4”x2” and there are several brushes common to each other around the perimeter.

    Back to scheduled program
    That brings back not so fond memories of as an apprentice standing on a step ladder in a track pit hunched over the top of a traction motor blowing out carbon dust and changing brushes.

    Thanks for that

  4. #19
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    4,978

    Default

    Quote Originally Posted by racingtadpole View Post
    To go off on a tangent for a moment..
    The DC fuelled locomotives at work have a length of 1 1/4” x1/4” copper braid connecting them to the primary traction bus, using 5/8 bolts torqued to some ridiculous level that requires the use of a hydraulic nut spinner. The brushes themselves are about 4”x2” and there are several brushes common to each other around the perimeter.

    Back to scheduled program
    Hi Adam, Guys,

    Like this one photographed in the "Blists Hill" village museum near Telford in the Midlands, UK.

    29-01-2019-055.jpg

    You can see the four rows of four brushes round the commutator.
    Best Regards:
    Baron J.

  5. #20
    Join Date
    Oct 2015
    Location
    melbourne
    Posts
    420

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    The donor
    20210826_203659.jpg
    The outcome, after a bit of filing.

    20210826_203433.jpg

    I'll try it out tomorrow. What could go wrong?

  6. #21
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    4,978

    Default

    Quote Originally Posted by russ57 View Post
    The donor
    20210826_203659.jpg
    The outcome, after a bit of filing.

    20210826_203433.jpg

    I'll try it out tomorrow. What could go wrong?
    Hi Russ,

    I notice that you have left a step on the sides ! Bad idea, those steps will cause the brush to arc onto the next segment of the commutator.

    I don't file my replacements, I use a belt sander and then a sanding stick (sandpaper glued to a piece of wood) to finish them off to size.
    Best Regards:
    Baron J.

  7. #22
    Join Date
    Oct 2015
    Location
    melbourne
    Posts
    420

    Default

    Thanks for the advice baron

    I left the step because it is only just wide enough. I figured that would help keep it centred and prevent rotation.
    In normal operation, there is a brief time where two segments are in contact as a typical brush is much wider than the gap between the segments.
    I'll only replace the one faulty one, so even if it does contact the adjacent commutator segment for longer, the same won't happen on the opposite side so shouldn't get any extra current flow.

    I will smooth the end off a bit, and will check for any sign of arcing after a few minutes running.

    (this brush seemed pretty soft - i reckon it would disappear on a belt sander...

    (and i am still looking for a better match brush)

  8. #23
    Join Date
    Apr 2018
    Location
    Perth
    Posts
    100

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    Quote Originally Posted by BaronJ View Post
    Hi Russ,

    I notice that you have left a step on the sides ! Bad idea, those steps will cause the brush to arc onto the next segment of the commutator.

    I don't file my replacements, I use a belt sander and then a sanding stick (sandpaper glued to a piece of wood) to finish them off to size.
    Just be wary of carbon dust, can cause health issues.

  9. #24
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    4,978

    Default

    Hi Russ, Guys,

    Some brushes are much harder than others. The ones that I'm using and cutting up are much harder than the original ones.

    Its basically a balance between brush and commutator wear. Strong springs and a hard brush will last longer but will wear the commutator more. In my case the brush is about 5 mm longer than the original and the spring is more compressed, theoretically giving me a better conductivity between the spring and brush. I did experiment with turning a little boss on the end of the brush for the spring to grab onto, but found that it didn't make any measurable difference to the resistivity of the assembly.

    Sparksy: Yes I do wear a dust mask when sanding the brush material, I also try to do it outside as well.

    Its a good idea to wear vinal gloves as well, the dust gets into your skin and its a right pain to wash off.
    Best Regards:
    Baron J.

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