Announcement

Collapse
No announcement yet.

Today's bodge

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Today's bodge

    Well more a 'technical repair'



    Set of three slip rings out of a big AC motor, big buggers these at 6-1/2" diameter and 1-1/4" wide but been skimmed that many times they were below the insulation and another skim would have open the winding gaps up.

    Normally I'd machine three new rings up and press them on in position then re-skim.

    In this case because it was below it couldn't be pressed on plus have you priced 7" diameter brass lately ? I was quoted £48 per slice, about $90 each. <gulp>
    No tube was forthcoming at these sizes and believe it or not thick walled tube is more expensive than solid.

    So 1-1/4" x 5/16" brass strip rolled into a ring and brazed on.
    Three rings shown in various stages, untouched, skimmed and ring fitted awaiting brazing and lastly a finished ring.

    So another expensive and special motor lives to burn another day.

    .
    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.




  • #2
    John..it just dawned on me that I'm missing something here. I don't know of anyone here who fixes electric motors like you do. I'm thinking they either must send them out or throw them away. I may just have to check this out with the local electric motor (robbers) outfits. Perhaps I can rob them for a change.
    Good idea on the rolled ring. So do you braze it solid all the way around on both sides? The finished one shows no signs of any seam or anything. Nice work.
    Russ
    I have tools I don't even know I own...

    Comment


    • #3
      Russ,
      I do work for three local rewind companies, one is only small, one is quite big and one specialises in DC and specials.
      Unless it's special I don't get run of the mill work as it's cheaper to throw it away and buy new.
      I mainly get motor parts like housing or rotors to rebuild when they have run a bearing.
      Under normal circumstances I don't actually do motors only parts they send, and often don't even know what they are off.
      The only exception to this is having a new motor delivered with an old one and being asked to make them the same, that's usually restricted to extending shafts, different diameters or fitting a gear pinion to the end.
      I also often have to modify flanges to fit obsolete gearboxes or adaptor plates.

      DC work is quite interesting as they will repair sooner than buy new.
      A largish fork truck motor can cost 2K upwards so cost isn't a problem.
      Unlike AC rotors where you can press a shaft out and replace you can't remove a shaft from a DC armature without crushing the windings between the stator and commutator and 9 times out of 10 they don't want to rewind these as it's so costly.
      Many don't have wire but shaped copper strips that are expensive to replicate and unlike older motors where the strips are soldered into slots on the comm modern DC motors have the strips resistance welded into the comm.
      This then spawns another job off of milling the welded bits out the comm, not hard but time consuming.

      Those rolled rings were cut so there was a small 1/8" gap at the ends of the ring and clamped to the old slip ring. They were then brazed with brass rod and using the TiG all round on both sides then the gap was filled.
      Once skimmed up in the lathe you can't see a visible joint except for the colour difference.
      It's interesting work as it always varies a bit and being geared for it means I can work cheaply but still make a profit.
      It's no good hitting them with big bills as you only get a couple of jobs and price yourself out the market.
      The secret is to be competitive but get return work, those slip rings, start to finish took 2 hours to do the three rings.

      .
      .

      Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



      Comment


      • #4
        John -

        Thanks for posting these jobs - I always learn something from watching you work!


        Cheers,

        Frank Ford
        FRETS.COM
        Gryphon Stringed Instruments
        My Home Shop Pages
        Cheers,

        Frank Ford
        HomeShopTech

        Comment


        • #5
          Well, I've seen some genyoowine bodges on occasion, and IMO that doesn't qualify. Of course this is an amateur opinion.

          Actually, very, very nice. Good solution and astonishing as a two hour job.

          JM
          .
          "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

          Comment


          • #6
            When John gives his times on jobs like this I just shake my head. I know he isn't lying so it makes him one of the quickest machinists on the planet. All his work looks perfectly suited to the job at hand as well.

            That'll be ten quid John.
            Free software for calculating bolt circles and similar: Click Here

            Comment


            • #7
              Originally posted by Evan
              makes him one of the quickest machinists on the planet.
              Ya...that's something else I missed. It'd prolly take me two days to do one of them
              Thanks for the info John!
              I have tools I don't even know I own...

              Comment


              • #8
                Yes, nice work, and faster than I could have done it. Well, I couldn't have done it, I don't have the equipment, but still. I have one question, and that's regarding the use of brass- isn't it better to use copper? They're slip rings, meant to conduct current, copper is a better conductor, etc. What am I missing?
                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                Comment


                • #9
                  Originally posted by Evan
                  When John gives his times on jobs like this I just shake my head. I know he isn't lying so it makes him one of the quickest machinists on the planet. All his work looks perfectly suited to the job at hand as well.

                  That'll be ten quid John.
                  There is a lot to be learned from watching and listening to people like John who have spent most of their life working in a machine shop. I work in a shop with a guy who can fix most things before most of the other guys have figured out what needs to be done. I've learned a lot from him and he is always willing to help and teach if you are willing to learn.

                  Great fix John and thanks for sharing your tips. I always enjoy seeing different ways of fixing things.
                  Jonathan P.

                  Comment


                  • #10
                    what did you use to roll the ring and how did you fit the ends well enough to braze, just cut and file? I did this recently with steel using a torch and there was a hell of a lot more clean up needed than i see in the ring you made
                    in Toronto Ontario - where are you?

                    Comment


                    • #11
                      Originally posted by darryl
                      Yes, nice work, and faster than I could have done it. Well, I couldn't have done it, I don't have the equipment, but still. I have one question, and that's regarding the use of brass- isn't it better to use copper? They're slip rings, meant to conduct current, copper is a better conductor, etc. What am I missing?
                      Copper galls and produces grooves that hold the brushes off in slip ring applications which causes arcing which erodes the rings and eats the brushes in short order.Brass or Bronze is a better choice since it is a bearing material but also a decent conductor.

                      Nice work on the slip rings John,that's one job I too get every so often.Largest set I ever did was 14" od and 2" wide along with the bakelite insulators.
                      I just need one more tool,just one!

                      Comment


                      • #12
                        make yourself a little foundry john, then you can cast 1/2 a dozen at a time, , i'll be round later with my vernier to check them measurements, they look a bit dodgy to me,,,,ony pulling yer leg. good work.

                        Comment


                        • #13
                          Wow, I would not have imagined the joint would be so smooth and well, basically jointless looking. It should be electrically sound.

                          But, the brazing is only so deep, right? Will it fail when the sleeves are wore (or skimmed) below the surface of the "good" joint.

                          Or are you able to some how create a "deep" braze joint extending all the way down to the parent metal.

                          I like your ingenuity and your work John...JRouche

                          Oh, maybe I missed it. You brazed the perimeter of the ring? So, even with wear or re-surfacing the hold will be tight? I like... Are the ends of the ring a flat butt joint or beveled in some way...Smart work...

                          Show the ugly part, yeah, after the braze bead is applied, before machining..

                          Do you loose some thickness of the original ring from machining the sides (braze bead) down?

                          Yep, that is smart work there John...
                          Last edited by JRouche; 02-02-2007, 10:21 PM.

                          Comment


                          • #14
                            I could do that job in about two hours...

                            I could do that job in about two hours. That is after I waited two days for the big (expensive) chunks of metal to make new ones out of arrived. I would never think to do it that way, or at least not before being blown away by more of Sir Sudspumpwater's brilliant execution. I keep saying we should all be able to get continuing ed credits just for reading his posts.
                            James Kilroy

                            Comment


                            • #15
                              Wow I didn't realise what interest a wierd job like this would attract so a few answers.
                              Most asked question is on the joint and if it will open up on reskimming. I rolled the rind on a cheap ring roller similar to this one.
                              http://www.toolsplus1.com/basic_ringroller.htm
                              these leave flats on the end sof the rings so you have to use a longer piece and cut the flats off or hammer them to continue the curve.
                              In my case I cut them off and left a gap of about 1/8" so I could fill this with braze onto the parent ring so technically there should be no gaps.
                              In time as they are skimmed it will get back to the parent ring and open up but it has 1/4" of material to wear away first.
                              Probably lost 10 thou on each side in the clean up but they are well oversize to the brushes and most brush gear is fully adjustable in mounting so you can centralise them.

                              Weirdscience has answered the question on material so that that's covered.
                              This is the first time I have used strip to do this, normally I turn the old rings down and shrink a sleeve over each but these were below the insulation and so had to be stripped down. A couple of years ago I'd have made new or still sleeved them but brass prices have gone stupid due to the Chinese buying up all the copper.

                              Billy boy is also correct - good eyesight, they do differ in diameter each ring was machined to just clean up, no idea what size they are, never measured them and it doesn't matter as the brushes are spring loaded. All that matters is they have as much life as possible on them.

                              .
                              .

                              Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



                              Comment

                              Working...
                              X