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Homework Help: How do I understand this gear diagram?

  1. Jan 1, 2017 #1
    I'm finding it a bit too confusing to imagine how it actually would look like. But once I understand that, I'd easily be able to solve the problem!

    link: http://i.imgur.com/DApJzGx.jpg

    The attempt at a solution:
    I'm thinking that the dotted line might be the place where the gears mesh, however that assumption isn't helping me to make any advances.
  2. jcsd
  3. Jan 2, 2017 #2


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    I'm fairly confused too.
    I would say that in 1 and 4 only the top halfof the gear is shown, whereas for 2 and 3 the whole gear is shown. 1 and 2 mesh at the parallel horizontal lines, likewise 3 and 4.
    From the diagram, I would have said 1 and 4 were connected by being on a common shaft, but that does not make sense given the other information. So I have to guess that 2 and 3 are supposed to be on a common shaft.
    There does not seem to be enough information to answer either a or b in isolation, but I see only one combination of answers that works.
  4. Jan 2, 2017 #3


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    Gears 1 and 4 are on a common axis but can rotate independently .

    There is to be a shaft between gears 2 and 3 . Correct meshing of all gears is only possible if the number of teeth on gear four is chosen so that the centre distances of gear pairs 1 to 2 and 3 to 4 are the same .
    Last edited: Jan 2, 2017
  5. Jan 2, 2017 #4
    It certainly looks like a shaft was omitted between gear 2 and gear 3. If this is included, then the result is an epicyclic train. Correct meshing is assured because we are given that all gears have a common module. The dotted line is nothing more than a center line, not a physical shaft.
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