Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Gear basics - changing axis of rotation

  1. May 22, 2010 #1
    hi everyone! I'm sorry if this seems like a really easy question, but...

    Suppose I have a device in which manually rotating gear A clockwise causes gear B to rotate clockwise. If gear A and gear B are at a weird angle to each other (say 35 degrees), what sort of intermediate parts could I use to achieve this rotation?

    I've been reading about bevel gears and helical gears, but it seems like bevel gears are only used to change the axis of rotation by 90 degrees? I could be mistaken. Any thoughts on possible configurations are appreciated! Especially well-known configurations for this kind of thing.

    (sorry if this seems really noobish! I'm actually a comp sci student with this newfound interest in mechanical engineering as of this summer.)
     
  2. jcsd
  3. May 22, 2010 #2

    Averagesupernova

    User Avatar
    Science Advisor
    Gold Member

    Just have the driven gear turned around facing the opposite direction.
     
  4. May 23, 2010 #3
    The axes don't have to be at 90 degrees, that's just probably the most common configuration.
     
  5. May 23, 2010 #4
    oh cool! so bevel gears specifically can be used at random angles like 35? or other types?
     
  6. May 23, 2010 #5

    jack action

    User Avatar
    Science Advisor
    Gold Member

    http://en.wikipedia.org/wiki/Bevel_gear" [Broken]:

    Beve_gear_schematic.png
     
    Last edited by a moderator: May 4, 2017
  7. Apr 14, 2011 #6
    what about helical gears?
     
  8. Apr 15, 2011 #7
    What about them?
     
  9. Apr 17, 2011 #8
    can they be used at random angles? 120 degrees?
     
  10. Apr 20, 2011 #9
    I believe that Helical can only be used at angles similar to that of "Spur gears" (the one most commonly seen by younger kids, the basic one). Basically they can be parallel-axis or cross-axis.

    parallel:
    cross:
     
    Last edited by a moderator: Sep 25, 2014
  11. Apr 23, 2011 #10

    Averagesupernova

    User Avatar
    Science Advisor
    Gold Member

    I don't believe that is true. I cannot think of an exmple though. But if they work at 0 (or 180, whatever you choose to call it) and 90 I cannot believe they cannot work anywhere in between.
     
    Last edited by a moderator: Sep 25, 2014
  12. Apr 24, 2011 #11
    Only parallel or cross axis. They cannot be used at any angle in between because they sum of their helix angles is always 90 degrees. I probably explained that wrong but it's something along those lines....it just has to do with the geometry.
     
  13. Apr 24, 2011 #12

    Averagesupernova

    User Avatar
    Science Advisor
    Gold Member

    Gear1.jpg

    Gear2.jpg

    Gear3.jpg

    The first two pix are of an oil pump gear and the camshaft that drives it. Notice that the teeth are not cut at the same angle. The last pic is of 2 identical oil pump gears meshed. They are not meshed at 90 degrees although it looks like it. It is difficult to get a pic that shows this. So, are you saying that although they mesh, and they are meshing at an angle that is niether 90 degree cross or parallel, there is some reason why one would not drive the other?
     
  14. Apr 25, 2011 #13
    I don't know. But, I want to take back what I said in post #11. I still don't think you can set them different than parallel or 90 degrees, but I just don't fully understand why (and indeed, if)...and don't have time to figure it out right now.
     
  15. Jul 9, 2011 #14

    jack action

    User Avatar
    Science Advisor
    Gold Member

    Helical gear can be used at any shaft angle.

    From http://www.roymech.co.uk/Useful_Tables/Drive/Helical_Gears.html" [Broken]:

    [PLAIN]http://www.roymech.co.uk/images9/gear_helical_3.gif [Broken]
     
    Last edited by a moderator: May 5, 2017
  16. Jul 9, 2011 #15
    Bevel gears can be used at through a range of angles, but their shafts must be in the same plane. Helical gears can also be used through a range of angles, but the plane their shafts can be rotated in must be parallel planes. Worm gears can also be designed for use in a range of angles, their shaft alignments are restricted similarly to helical gears. There are also spiral-bevel gears (a combination of bevel and helical) and hypoid gears that can be used in a range of angles, their shaft alignments are not as restricted as for other types of gearing.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook