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  • I'm doing a favor for a friend

    who brought me a sealed Ball Bearing and a shaft for a Bush Hog that had been snapped in two and that he had welded back together. He wants me to turn down the weld so he can fit the bearing and return the borrowed machine to its owner.
    Question: How much difference do I make on the shaft as compared to the I.D. of the Bearing? I'm more accustomed to fitting Bronze Bushings than Ball Bearings is why I ask.

  • #2
    Hello Al,
    I would use .0015" to .002". If the bearing O.D. fits inside of a tight housing
    remember that the roller or ball clearance
    will be reduced by the amount of the interference fit on the I.D. In actual use
    a slight interference fit of .001" would work but for the use its being used for
    .0015" to .002' would be better.
    Yankee1

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    • #3
      Who broke it?
      Does anyone actually read siglines?

      Comment


      • #4
        Al,
        I suggest that you make a new shaft. There is no way for you to tell how good the weld is. The last man working on it is likely the one who will be blamed when it snaps again. If someone is injured when it flies apart there will be hell to pay.
        To invent, you need a good imagination - and a pile of junk. Thomas A. Edison

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        • #5
          Hey Al,

          I would agree with G.A. I have a bush hog at work and you should see the beating that thing goes through. I won't even make the knives for them as they are tempered. I would suggest making a new shaft. Just to be safe.

          Rob

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          • #6
            I agree with G.A. Ewen. Welding a shaft is chancy at best, especially one that may see some of the stresses of a brush hog with the possiblity of damage to life and property in the event of future failure.
            Jim H.

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            • #7
              Normally, I would agree about just making a new shaft, especially since I did not have anything to do with the shaft breaking, but, the guys responsible for it do not want to pay for a new shaft!! Thanks for the info though.

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              • #8
                If this is the main shaft that takes the cutter head make a new one of good material not just mild steel.

                Look at the shaft fracture. Chances are it's a classic fatigue failure and the fault of no-one but the equipment designer.

                Maybe it looks like this:

                http://images.google.com/imgres?imgu...aRcJ:&tbnh=90& tbnw=112&prev=/images%3Fq%3DMetal%2Bfatigue%2B%26hl%3Den%26lr%3D% 26ie%3DUTF-8%26sa%3DG

                The fracture likely propagated from a set-screw mark and looks silvery gray like it was brittle to part way across the shaft. Ultimate failure will look ductile.

                Help your buddy explain it to the machine's owner so he won't feel like his equipment has been abused. Ask him to spring for a piece of 4130 (how big is this shaft?). Explain the busted shaft cannot be safely welded and you'll take no part in a weld repair or the subsequent machining.

                If the bearing are pillow blocks the shaft is a slip fit (0.0005" to 0.0010" clearance). If the bearings were pressed on look up the press fit for bearings in that size and number for that service.

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                • #9
                  They may not want to pay, but you can bet the lawyers will want to make YOU pay if someone gets hurt.

                  Roger
                  Any products mentioned in my posts have been endorsed by their manufacturer.

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                  • #10
                    Years ago I was supervising a couple of Hydro Axe operators clearing a powerline ROW when one of the machines broke the main shaft. It was a short, thick, VERY EXPENSIVE piece of steel. The owner wasn't too concerned about it because they had a lifespan and he had gotten more time from it than he expected. Point here is, maybe the shaft that broke on the Bush Hog was at the end of it's lifespan and fatigue was the problem. Harsh work enviroment, eh?
                    Location: Saskatoon, Saskatchewan, Canada

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                    • #11
                      I think that the deal here is that the two "borrowers" do not want the "owner" to know that they busted his machinery. Some of these Tennessee farmers can be pretty touchy about their equiptment. Since the "borrowers" have done all the welding, why should I be responsible for anything other than turning it down to a correct tolerance?

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                      • #12
                        Because you may not be doing a favor for the friend or the owner of the machinery...and it seems like you may know a bit more than your friend about machinery, fractures, heat affected zones, etc. etc. And hence, have an obligation as a friend to teach these guys a thing or two. There also seems to be an ethical issue with these gentlemen hiding the fracture from the owner...anyway you're all adults and I'm not there to see the shaft so...

                        I'd mic an undamaged portion of the shaft and match that...or go 1~1.5 thousands max on the bearing fit.


                        <font face="Verdana, Arial" size="2">Originally posted by Al Messer:
                        I think that the deal here is that the two "borrowers" do not want the "owner" to know that they busted his machinery. Some of these Tennessee farmers can be pretty touchy about their equiptment. Since the "borrowers" have done all the welding, why should I be responsible for anything other than turning it down to a correct tolerance? </font>


                        [This message has been edited by abn (edited 03-01-2004).]

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                        • #13
                          Ok here is a question. If you were to machine down a ways, and make a coller to go on the shaft. Maybe make it a shrink fit. Weld it on, and then machine the the new sleeve to the correct tolerances. Wouldn't that make the shaft stronger? You would have the initial weld, underneath the coller and the coller would help spread the load over both sections. I figure that would help.

                          What do you all think?

                          Rob

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                          • #14
                            Al,
                            I wouldn't touch that with your ten foot pole.
                            A guy wanted to have me re-machine welded dump truck front end spindles once.
                            I asked him who would pay when it broke and killed a young mother and her two kids?
                            I told him to get bent.
                            mite

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                            • #15
                              I would question the quality of the weld. I doubt that it was beveled very far below the surface before welding. Are these guys certified welders or just farmer welders?

                              I use bush hogs and those shafts take a beating. I don't see how any repair could be safe. When the blades coming flying out the next time, some one could be seriously hurt or killed; probably the person driving the tractor.

                              Greg

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