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How To Remove & Install Plastic Wheels & Gears

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  • #16
    Wrong assumption, guys. We're talking about Ninco ProRace anglewinder gears -- metal-to-metal contact, no plastic.
    Wrong assumption about the materials maybe, but, still correct assumption that it had nothing to do with temperature/shrinkage. It just happened, sometimes things just do.

    Both the gear and the axle being metal, they would change temps at roughly the same rate(although the amount on the gear would be more because it is aluminum, and not steel, but, it would still not be enough difference to cause this effect).

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    • #17
      The spinning gear was secured with a setscrew? Had the screw loosened, or had the point of the set screw cut a groove around the axle? We'll get to the root of this . . .

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      • #18
        Badumbum

        If the axle had a bevel to it, then wouldn't we need to get to the square root of this?

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        • #19
          It had a setscrew, but that's irrelevant. As long as the axle/gear combo was warm, the car ran. When allowed to cool, the axle spun in the gear. Heated up again, and the performance improved again -- not enough to run the final, so I had to stop and tighten the setscrew.

          The performance could not have improved again without thermal expansion, if the assumption for the failure was that the set screw cut a slight groove in the axle.

          Al, never assume that two dissimilar metals will behave exactly the same way. If they did, you'd never have to knock a magnesium wheel off a steel hub with a hammer. Metals have similar properties, yes -- but the degree to which they exhibit these properties makes them substantially different. Every metal has its own coefficient of thermal expansion, for example. Every metal conducts electricity, but we don't use a lot of aluminum wiring in the house...

          "It just happened", sure. But there's a 'why' for everything that has ever 'just happened'.
          Last edited by ElSecundo; 09-10-2008, 03:52 PM.

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          • #20
            Al, never assume that two dissimilar metals will behave exactly the same way. If they did, you'd never have to knock a magnesium wheel off a steel hub with a hammer. Metals have similar properties, yes -- but the degree to which they exhibit these properties makes them substantially different. Every metal has its own coefficient of thermal expansion,
            I never assume anything

            I've spent most of my adult life working with thermal expansion (and shrinkage) of metals of all types and shrink fits, press fits loose fits, hand push fits, you name it, so, trust me, I am pretty well versed in this stuff.

            Your phenomenon would have much more to do with the dissimilarity in the metals compositions themselves, than in the thermal expansion differences between them. The most likely cause, would be just plain old friction, and, galling of the aluminum gear on the steel axle. The spinning steel axle in the aluminum gear would start to pickup microscopic particles which weld themselves to the steel axle due to friction. I'm not just guessing or assuming here, I have actually seen this happen, and, have verified this sort of condition on many occasions. I'm pretty sure that if you take the gear off the axle you will see traces of Aluminum welded onto the axle.
            Last edited by BWA; 09-10-2008, 07:23 PM.

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            • #21
              That's possible, Al. So what's your hypothesis? Here are the facts, so how do you account for these:

              1) Set screw loosens (don't need a hypothesis here)
              2) Gear starts to slip. Car runs very well for four heats once it starts to slip (let's say 10%-20% slippage).
              3) Car sits for a period of time.
              4) Car starts on grid, axle suddenly unable to drive the car (90% slippage)
              5) After a fair amount of slip, axle steadily begins to reduce slippage (back to about 50% slippage)

              Anyway, the specific evidence points to the possibility of thermal expansion and contraction, and the idea here is to try it on a wheel/axle combo to see for sure.
              Last edited by ElSecundo; 09-10-2008, 11:42 PM.

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              • #22
                5) After a fair amount of slip, axle steadily begins to reduce slippage (back to about 50% slippage)
                The most likely cause, would be just plain old friction, and, galling of the aluminum gear on the steel axle. The spinning steel axle in the aluminum gear would start to pickup microscopic particles which weld themselves to the steel axle due to friction.
                Once enough Aluminum particles get stuck to the axle, they fill the gap between the gear and axle, and, you get drive. This can sometimes continue to the point where the gear itself will actually become welded onto the axle, and, can be extremely difficult to remove. I have seen this myself, and, have actually seen it happen just assembling brand new components. If the gear (or wheel) is not anodized, and, the bore tolerance is very close, the gear or wheel can weld itself to an axle, just by pushing the axle through it, especially if you use a twisting motion to do this.

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                • #23
                  Originally posted by BWA View Post
                  Once enough Aluminum particles get stuck to the axle, they fill the gap between the gear and axle, and, you get drive. This can sometimes continue to the point where the gear itself will actually become welded onto the axle, and, can be extremely difficult to remove. I have seen this myself, and, have actually seen it happen just assembling brand new components. If the gear (or wheel) is not anodized, and, the bore tolerance is very close, the gear or wheel can weld itself to an axle, just by pushing the axle through it, especially if you use a twisting motion to do this.
                  That's an interesting and plausible theory. It still leaves a couple of holes, specifically if the 'welding' process is occurring, then letting the gear/axle combo sit for a while will not reverse the effect, which is what we saw in the race. But I'm in complete agreement that two dissimilar metals can 'weld' to each other. Dissimilar metals can create an intense electrostatic attraction, but this effect doesn't require that any particles are worn away by friction first. In fact, particles would prevent the two parts from welding to each other. The Al particles would weld to the steel axle forming an Al boundary layer -- and the Al boundary layer won't weld to the aluminum gear because the metals aren't dissimilar. But an Al layer could definitely build up the way you suggest. It would be a very thin layer, but might be enough to make a difference.

                  Now, all that said, and I just took an old Carrera chassis out of the freezer. One wheel popped right off without leaving plastic residue behind, the other was still stuck pretty good.

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                  • #24
                    I think the cold may be embrittling the plastic of the Carrera hub. If there is a tiny amount of steel axle contraction, that could be enough to fracture the plastic hills and valleys created by the knurl. Interesting experiment.

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                    • #25
                      Originally posted by Robert Livingston View Post
                      I think the cold may be embrittling the plastic of the Carrera hub. If there is a tiny amount of steel axle contraction, that could be enough to fracture the plastic hills and valleys created by the knurl. Interesting experiment.
                      One other effect we hadn't mentioned is that it's likely that at room temperature, there may be a tight seal between the compressed plastic and the steel. The slightest contraction may break that seal, even if the contraction isn't enough to completely free the knurls from the contours of the plastic.

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