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  • building up bearing seats

    good evening all.

    so somebody brought me this thing to fix,
    and i don't know what it is.

    hope thats enough info for you guys to work from.

    its a cast iron gearbox cover. in the (inside) center of the cover is a bearing seat. it holds a seal and a bearing.. allowing the shaft to exit the box.

    the bearing is largish (about 5" diam x 1.5" wide) and the casting is thin.

    the seat has worn about 5thou. tyipically i would weld this back up, then turn down to size after cooling.

    this time, the casting is so large/thin (it just barely fits in the lathe) that i'm afraid discontinuous cuts (the weld bead) will crack the casting. not to mention that i'm afraid to crank the chuck tight (i'm holding on an inside diameter.. about 2" opening on a 10lb casting.. and the wall thickness there is 1/8" max).

    considering brazing (silver) the bore up and turningthat to size. have never done that before and am unsure how a brazed bearing seat will last in the long run. thoughts? experiences?

    if brazing is ok, since the silver is softer, should i still use a 0.001-0.0015" interference fit, or more?

    optionally, i could open the seat up and press a bushing in.. but thats ALOT more work than i'd like to put into it.

    thanks,
    -tony

  • #2
    With a bearing that size you have a lot of seat area. Have you thought of building it up with something like Loctite metal epoxy?
    Free software for calculating bolt circles and similar: Click Here

    Comment


    • #3
      Tony,
      Believe me machining out and bushing is far quicker in the long run than any form of welding on cast motor housings.

      On the thinner castings you have a large difference between the webs needed to hold a bearing this size and the rest of the housing.
      Any heat will crack this housing.
      If they are cracked and HAVE to be welded it's a long job with it being required to be bolted to jigs during pre heat, welding and cooling.

      This is a job I do on a daily basis, I have done 4 today.
      You can buy the rings specially made for the job.
      http://www.shaverkudell.ca/products/sleeve.html
      They are finished on the OD but left undersize on the ID, you bore out, press a ring in and then bore to fit the bearing.

      Here's one I did earlier



      John S.



      [This message has been edited by John Stevenson (edited 09-16-2004).]
      .

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



      Comment


      • #4
        evan, hadn't considered the expoxy route.
        i have some locktite "Press Fit Repair" .. dont even know how it got into my toolbox. its not a two component epoxy, though. its grey and has the consistency of toothpaste.
        sounds like a good chance to experiment.

        john, the casting is not cracked. not sure what happened, but seems like an old bearing seized and wore the ID on the casting. the mechanic tells me that pulling the bearing was a PITA.

        careful measuring reveals bellmouthed seat. worn toward the shoulder, but still good on the 'outside' (where the lead-in is)... i bet it was tough to get out!

        usually i've TIG welded with nickel rods but the castings have never been this thin.

        as always its an 'emergency' repair. might be able to get away with 3 tack welds and boring it out in the mill. i'll try to figure out if it needs to be a good clean job, or if they just need to get up and running till replacement parts come in.

        thanks for the heads-up, points well taken.
        -tony

        Comment


        • #5
          John, that's a set of chuck jaws that I have never seen before, pretty slick. You need a can of paint from your good friend up north.

          Comment


          • #6
            Knucklehead, if you decide to go the Loctite route ensure that you have absolute cleanliness. For myself I would opt to take Johns advice.
            Ken.

            Comment


            • #7
              Tony,
              I wasn't saying it was cracked just that welding on these things causes more trouble than it's worth.
              Another way to go about this is to bore out and use tolerance rings.
              http://www.usatolerancerings.com/
              You don't have to hold such tight tolerances with these.
              Personally I don't like them, I have seen many hammered out under load but odd times where space is at a premium I have had to use them.

              Mike,
              They are called Greedy Jaws
              Just 'L' shaped pieces bolted to the face of a set of soft jaws. You can move them up and down to suit jobs and then just give them a lick to make sure they are running true.

              Sod the paint, this thing has to work for a living.
              I know it would look better painted but all my machines have to earn a living and nobody will pay me to paint them.

              John S.
              .

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



              Comment


              • #8
                <font face="Verdana, Arial" size="2">Originally posted by John Stevenson:


                Sod the paint, this thing has to work for a living.
                I know it would look better painted but all my machines have to earn a living and nobody will pay me to paint them.

                John S.
                </font>
                I bet if you offered Alistair 50 pence a machine he'd snatch your hand off. He'll have plenty of time in his school holidays.

                Allan

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                • #9
                  Talk to your bearing supplier about "tolerance rings".
                  Harry

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                  • #10
                    If there's not enough wall to bore it out, shrink in a sleeve with an undersized bore (1/8 min installation wall; 0.040" wall is plenty in a finished sleeve), you can always bore it out to a decent size, and sil-braze or silicon bronze weld in a new boss.

                    Epoxy is the last stuff I'd use to reclaim a worn bearing bore and then it would be a life or death situation and whoever it was at death's door was worth the effort to screw around with weak goo.

                    Comment


                    • #11
                      Chances are good that the bearing is not a press fit into the housing but a press fit on the shaft thus the worn bore. You may want to think about boring oversize and then pressing in lightly a sleeve which is tack welded to the housing and then boring the sleeve for a none press fit with the bearing. Check a bearing vendors manual for size.

                      ------------------
                      Neil Peters
                      Neil Peters

                      When on the hunt, a broken part is better than no part at all.

                      Comment


                      • #12
                        Epoxy isn't worth a light, believe me I do this every day for a living.
                        I have one housing in the lathe at the moment and two rotors built up ready to remachine and that's before I've opened the doors today.

                        There will always be exceptions but 99% of motors have the bearings pressed onto the rotor and they are a light fit into the housings.
                        They must be a light fit on one housing to allow for expansion hence the crinkle washer fitted to control end float.
                        The type of motor that have fixed bearing in the housings tend to be power tools and fan motors, usually small light duty units.

                        I usually bore to about a thou below and polish out the tool marks with a bit of emery cloth to get to size.
                        I try to aim for a tight push fit, light tap fit.

                        John S.
                        .

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



                        Comment


                        • #13
                          But it's a gearbox, not a motor.
                          Free software for calculating bolt circles and similar: Click Here

                          Comment


                          • #14
                            Build up the worn bore with brush plated hard nickel. Re-bore or grind to size if needed.

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                            • #15
                              <font face="Verdana, Arial" size="2">Originally posted by Evan:
                              But it's a gearbox, not a motor.</font>
                              So ?
                              it's a bearing housing.

                              .

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



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