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repairing damaged gear bore

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  • repairing damaged gear bore

    I'm repairing a lathe that had the keyway torn out. I've welded it back up and turned it down to clean it up.

    Between my turning down slightly and the wear in the pulley, I have a over sized condition. Pulley is cast iron.

    I'm thinking of boring out pulley for an insert pressed in that matches the shaft I repaired.

    What is the best way to pin it in place?

    Thanks,

    Clutch

  • #2
    You could make your Bush slightly oversize depending on its diameter(rule of thumb is .001" to the inch) and Heat your pulley so that the bush slips into it,you could even have the bush in the freezer to shrink the bush to assist in your interference fit.
    After woulds if you are still concerned about your bush comming loose you could Scothch dowel it with either a small grub screw or roll pin.
    Just drill one or two small holes to suit grub screw or roll pin in the centre of the pcd of the gear and bush repair.

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    • #3
      Bore the whole hub off, make a big shoulder bushing, weld it in with econocast rod. once its cool bore and key it and call it done.

      Thats what we call "bore and slug."

      Cast iron welding is not hard to do, machine chamfers for weld, pre heat with a torch. weld it with at least 100 amps. peen the weld with a chipping hammer till your arm hurts. do a post heat and throw it in a bucket of ashes so it cools real slow. the weld should turn out as ductile and machinable as you could ever ask.

      Also it would be wise to go ahead and weld up the shaft and turn and re-key it too. make all the parts back to spec.

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      • #4
        Ever think of using Loc-Tite?

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        • #5
          How much interference are you going to have or is it going to be a sliding fit.
          Does the part get hot,this can weaken the loctite.

          Comment


          • #6
            A pulley? Is this for a drive belt? What is the ID of the hole and the OD of the pulley? If for a Vee belt the OD is at the bottom of the groove.

            Gray cast iron has poor tensile yield strength. It ranges from about 9ksi to 25 ksi depending on grade. Ultimate Tensile strength is about 1/3 the compressive strength. Using an interference fit can crack the iron if the OD is not a lot bigger than the ID, especially since the insert will have much greater compressive strength than the part has tensile strength.
            Free software for calculating bolt circles and similar: Click Here

            Comment


            • #7
              Back to basics

              Let's go back to basics and "square one" and not get side-tracked by the possibly unnecessary more exotic options - again.

              Instead of boring and pressing or welding or using Loctite alone, why not just clean the bore up face-off, than screw cut the bore. Make a flanged screwed sleeve to suit and screw it in to pre-screwed gear right up hard to the flange. By all means use Loctite (correct grade of course) and then bore - and key? - the bore to suit the shaft. Only thing to watch is the direction of rotation of the pulley so that it tightens the thread instead of loosening it. Think right and left-hand threads on grinders and why they are used.

              You can make the screwed sleeve from any material that suits you. Just like the thread on a lathe back-plate fitting on the spindle screwed nose.

              No need for press fits or welding or shrink-fitting and possible cast-iron fractures.

              If needed a pin or screw can be fitted to "keep" the flange if needs be - but I'd doubt it would be necessary.

              Comment


              • #8
                Originally posted by pipeclay
                You could make your Bush slightly oversize depending on its diameter(rule of thumb is .001" to the inch) and Heat your pulley so that the bush slips into it,you could even have the bush in the freezer to shrink the bush to assist in your interference fit.
                After woulds if you are still concerned about your bush comming loose you could Scothch dowel it with either a small grub screw or roll pin.
                Just drill one or two small holes to suit grub screw or roll pin in the centre of the pcd of the gear and bush repair.
                Evan made a reference to press fits and cast iron, I have no problems with a press fit, just don't want to crack it.

                The grub screw, are you talking about tapping the hole short of though and setting a screw coated with locktight?

                The roll pin also sounds interesting, never heard that one before.

                Clutch

                Comment


                • #9
                  Originally posted by tattoomike68
                  Bore the whole hub off, make a big shoulder bushing, weld it in with econocast rod. once its cool bore and key it and call it done.
                  That is an interesting suggestion.

                  Originally posted by tattoomike68
                  Also it would be wise to go ahead and weld up the shaft and turn and re-key it too. make all the parts back to spec.
                  The minor reduction in diameter isn't that big a thing. The chance that I mess up the threads on both sides of the shaft is very high. Lathe is not heavily stressed.

                  Clutch

                  Comment


                  • #10
                    Originally posted by Al Messer
                    Ever think of using Loc-Tite?
                    How well does loc-tite work with an interference fit?

                    Clutch

                    Comment


                    • #11
                      Originally posted by Evan
                      A pulley? Is this for a drive belt? What is the ID of the hole and the OD of the pulley? If for a Vee belt the OD is at the bottom of the groove.

                      Gray cast iron has poor tensile yield strength. It ranges from about 9ksi to 25 ksi depending on grade. Ultimate Tensile strength is about 1/3 the compressive strength. Using an interference fit can crack the iron if the OD is not a lot bigger than the ID, especially since the insert will have much greater compressive strength than the part has tensile strength.
                      I errantly used gear when it is a pulley. There is enough wall to press in an insert. I'm not against using CI rod and welding it in. As it is, the ~ 1 inch shaft uses a 3/16w by 7/8 dia woodruff key.

                      I can buy a piece of 2" cast iron rod and some cast iron welding rod to use TT..Mike..'s suggestion.

                      Comment


                      • #12
                        Originally posted by oldtiffie
                        Let's go back to basics and "square one" and not get side-tracked by the possibly unnecessary more exotic options - again.

                        Instead of boring and pressing or welding or using Loctite alone, why not just clean the bore up face-off, than screw cut the bore. Make a flanged screwed sleeve to suit and screw it in to pre-screwed gear right up hard to the flange. By all means use Loctite (correct grade of course) and then bore - and key? - the bore to suit the shaft. Only thing to watch is the direction of rotation of the pulley so that it tightens the thread instead of loosening it. Think right and left-hand threads on grinders and why they are used.

                        You can make the screwed sleeve from any material that suits you. Just like the thread on a lathe back-plate fitting on the spindle screwed nose.
                        I think that is overkill but if you check
                        http://wess.freeshell.org/clausing/Clausing.html

                        You will see I used that idea repairing a sheave once upon a time.

                        Clutch

                        Comment


                        • #13
                          I can buy a piece of 2" cast iron rod and some cast iron welding rod to use ...

                          One note about cast iron welding rod; the kind that is commonly available here is what I used to hard face the bucket teeth on the back hoe. It is entirely unmachinable except by grinding.
                          Free software for calculating bolt circles and similar: Click Here

                          Comment


                          • #14
                            Gordon Bennett what a palaver over a 10 minute job.

                            It's cast iron so no interference fits or welding if you don't want it to crack.

                            Bore out, make sleeve for slip fit, loctite in and then drill two holes on the joint so 1/2 in in the pulley, half in the sleeve, fit a couple of Allen grub screws and nip up.

                            If you have no grub screws fit a long ordinary screw and cut the excess off, it isn't like it needs to be disassembled at any point does it ?

                            .
                            .

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



                            Comment


                            • #15
                              Originally posted by clutch
                              How well does loc-tite work with an interference fit?

                              Clutch
                              Locktite cures in the absence of air. Once together you'll have the devils own time getting them apart.

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