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Train wreck caused by broken aluminum part

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  • Train wreck caused by broken aluminum part

    I built a quarter scale train in my backyard for my granddaughter ( that has plywood wheels with the wheel flange made from an aluminum 12" diameter v-pulley with one side of the V milled off. The pulley failed catastrophically due to a combination of bending and metal fatigue. My question is whether this pulley can be fixed by straightening and welding, or whether I need to just replace the pulley.

    Replacing it may be problematic, unless I can find the exact same version of the pulley. The wheel assembly comprises dozens of parts made specifically for this pulley. In addition to the cost of the pulley (about $35 - $40), I'll have to find a machine shop that can turn it on a lathe to remove one of the flanges.

    I've posted some pictures that should show where the breaks and bends are. So I'm just wondering what is the collective consensus of the welding community about how I should go about repairing or replacing this. I probably should mention that I've never welded and don't have any welding experience. So if the pulley can be fixed, I'll need to know what skills and equipment I should be looking for in a machine shop.

    Thanks for all of your replies.

  • #2
    That appears to be the type of pulley used for the blower wheel on evaporative coolers. I think I paid less than $20 shipped when I last bought one from Amazon.

    As for milling off the one edge, does it HAVE to be that pretty and precise? The proper aluminum cutting disk in a grinder, followed by the proper disks for grinding and sanding would probably do a very acceptable job.

    That is a cast aluminum part. I'm no expert at welding aluminum, but many of those cast parts are not a weldable alloy.

    What caused the failure? Is it likely to happen again?


    • #3
      The milling on the cut flange edge does not need to be precise. I took it to my auto mechanic when I originally built the wheel and he turned it on his brake lathe (had to make some modifications to handle the larger diameter). He's no longer in business. I would have just ground the flange on my bench grinder, but my experience with grinding aluminum is that it quickly clogs the grinding wheel. Is there a special wheel for aluminum? Another concern I wonder about is the hazard (health and explosive) with creating fine aluminum dust. So I'm open to grinding the flange myself, but would need to have a little more knowledge than I currently have about the process. And is heat a concern if I grind it? Should water be involved?

      As far as the cause of the break, if the train (which weighs about three hundred pounds) climbs the rail because of a stick on the track, then the edge of the flange takes the full weight. If the train has some momentum, that compounds the force on the edge. I've had to bend the flange back a few times to straighten it out. I guess the metal fatigue finally reached a tipping point.

      Based on about a year's worth of experience, I think I can replace the half-inch wood pie-shaped inserts on the back of the wheel (used to sandwich the pulley between the the inside and outside of the wheel assembly) with three quarter plywood that's cut to ride against the outer edge of the flange and provide some backing support. That way, if the flange takes the full weight in a derail situation, the stress will be absorbed by the plywood back instead of the aluminum flange. Live and learn. I'll call that running gear V2.0.


      • #4
        Can you find a suitable replacement pulley made from steel ?
        It would take more weight and wear better in the long run ,may need to take it to a foundry and have one cast off the old one as thin as that aluminum is I think your gonna keep having the same problem especially if kids are on it safety would be a concern .
        Also if the new steel mating surface ever started to wear you could have someone build it up with hard facing welding rod and grind or machine it in a lathe to make it true again.


        • #5
          I too would use steel...Bob
          Bob Wright


          • #6
            I have had problems welding some cast or
            die cast Aluminum parts due to the composition of the alloy. In answer to your question regarding grinding wheels for Aluminum, if you use a grinding wheel designed for Aluminum it won't load up. For example:


            Last edited by Don52; 06-24-2017, 10:36 AM.
            Smith Oxyacetylene Torch
            Miller Dynasty 200DX
            Lincoln SP-250 MIG Welder
            Lincoln LE 31 MP
            Lincoln 210 MP
            Clausing/Colchester 15" Lathe
            16" DoAll Saw
            15" Drill Press
            7" x 9" Swivel Head Horizontal Band Saw
            20 Ton Arbor Press


            • #7
              Anyone near you handy with a torch? I'd be inclined to bend (roll) a couple of pieces of angle, flange out to make tires for your wooden wheels and then screw them to the wheels. I would guess that they could be done close enough to round for the job at hand. Casting would be great but I think you would find it expensive. Any scrap yards/dealers near you? Sometimes you can find old cable sheaves in cast iron or steel that might do for this as well. What might work is wheels from a cultipacker if you could find one scrapped in your vicinity. These ones are too small I think and there are some made without notches.


              • #8
                Since it appears that the pulley just provides an outer rim/lip/flange for the wheel, why not just replace the pulley with a plasm-cut steel plate of the appropriate diameter to provide the lip, and never worry about failure, again?
                Last edited by Goodhand; 06-26-2017, 11:59 PM.


                • #9
                  I am almost 100% certain that your pulley is a predominately zinc die casting alloy that is virtually unweldable. It's not very fatigue resistant either. You should consider redesigning with a stronger material.

                  80% of failures are from 20% of causes
                  Never compromise your principles today in the name of furthering them in the future.
                  "All I ever wanted was an honest week's pay for an honest day's work." -Sgt. Bilko
                  "We are generally better persuaded by reasons we discover ourselves than by those given to us by others." -Pascal
                  "Since we cannot know all that there is to be known about anything, we ought to know a little about everything." -Pascal


                  • #10
                    Are your wooden wheels beveled for going around curves? The flange shouldn't ever touch the rail
                    Last edited by digr; 06-29-2017, 09:53 PM.