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Gear Script Question

Discussion in 'Using Alibre Design' started by RocketNut, Mar 14, 2020.

  1. RocketNut

    RocketNut Alibre Super User

    ( ͡° ͜ʖ ͡°)

    I have done gear design before using gears I found online. I want to use the Gear Generator Script example to do a new design. Which needs a 1:4 ration, with drive gear having 20 teeth and the output gear has 5 teeth. How can I get this ration used the Gear Generator Script?
  2. albie0803

    albie0803 Alibre Super User

    Well.... in reality the amount of force you want to transmit will define the size of the tooth, but.....
    What is the largest size the 20T gear can be.
    Will you be using DP or Module gears?
    Will you have a set centre distance you want to work to?

    "Standard" gears have a set centre distance but you can vary this if you want to work to different distances.

    The gear generator script produces "standard" gears.
    Below are gearsets as they would actually look from the GearCAD program we use at work

    This is 5/20 gearset: (you may have trouble getting a 5T commercially due to the excessive undercut)
    At 1DP: OD's are 7"/22" and centre distance is 12.5"
    At 4DP: OD's are 1.75"/5.5" and centre distance is 3.125"
    At 8DP: OD's are 0.875"/2.75" and centre distance is 1.5625"

    This is 8/32: (the undercut in the 8T still isn't real good)
    At 1DP: OD's are 10"/34" and centre distance is 20"
    At 4DP: OD's are 2.5"/8.5" and centre distance is 5"
    At 8DP: OD's are 1.25"/4.25" and centre distance is 2.5"

    this is 10/40: (this is better)
    At 1DP: OD's are 12"/42" and centre distance is 25"
    At 4DP: OD's are 3"/10.5" and centre distance is 6.25"
    At 8DP: OD's are 1.5"/5.25" and centre distance is 3.125"

    and this is 12/48: (This is best)
    At 1DP: OD's are 14"/50" and centre distance is 30"
    At 4DP: OD's are 3.5"/12.5" and centre distance is 7.5"
    At 8DP: OD's are 1.75"/6.25" and centre distance is 3.75"

    To work out what DP you want, take the number of teeth in a gear, add 2 and then divide by the OD (inches) you want for the gear.
    The answer to the nearest .5 above the answer (8.3 = 8.5, 7.6 = 8) is the DP you want to fit your gearset in the available space.

    To use the Gear Generator script as it is: Pitch Diameter = DP x Teeth and use 20° for the pressure angle.
    The correct centre distance will be: Sum of the 2 Pitch Diameters / 2 | (PD1+PD2)/2

    I hope all that is a little "clearer than mud" for you. ;)
  3. RocketNut

    RocketNut Alibre Super User

    I agree 48:12 teeth would be the best number of teeth.

    I do not understand your statement:

    Also, my units are mm. Does that change the exquestions?

  4. Lew_Merrick

    Lew_Merrick Alibre Super User

    Other than defining gear in Module rather than Diametral Pitch (Module = 25.4/Diametral Pitch) not ant difference. -- Lew
  5. RocketNut

    RocketNut Alibre Super User

    Thanks, Lew :)

    What is the most common Module or Diametral Pitch when defending a gear?
    I miss understood albie0803 equation: Sum of the 2 Pitch Diameters / 2 | (PD1+PD2)/2. The " | " through me. Now everything is clear and works.

    I saw somewhere there is a constraint for gear meshing. Where can I find that constrain?

    Again thanks for the great help.
    Last edited: Mar 15, 2020
  6. Ralf

    Ralf Alibre Super User

  7. RocketNut

    RocketNut Alibre Super User

    Thanks for the link Ralf

    I guess I have to wait for the next major update to get the gear constants. :(:(

    Does anyone know when it will be released?
    Last edited: Mar 15, 2020
  8. Lew_Merrick

    Lew_Merrick Alibre Super User

    Hi Richard -- What I do is to add a component to the Gear Model that is a Cylinder centered on the Gear that is the Pitch Diameter of the Gear. I "Hide" that after it is complete (and "adjust" the Density" to make the Mass come out right). I can then "Constrain Tangency" to the "Mating Gear" (Pitch Diameter component) when required. -- Lew
  9. Ralf

    Ralf Alibre Super User

    Richard, please take a look:
  10. RocketNut

    RocketNut Alibre Super User

    (brushing bright red face) I did not see that realase date when I first looked at your link.:oops::oops:

    That is this month. :D:D:D

    One last question. How do I spec a gear in a drawing?
  11. albie0803

    albie0803 Alibre Super User

    If it will be an "off the shelf" item then 48T 10DP 20°PA x 1" wide or 48T 2.5Mod 20°PA x 25mm wide will be fine. It will have been made with "general application" backlash.
    If the gearset has been fiddled, eg centre distance changed, then a lot more detail is required for the manufacture of the gears.
  12. Lew_Merrick

    Lew_Merrick Alibre Super User

    Sorry, I could not find the "Gear Undercutting" document I wrote in the 1970's (with Electric Pencil no less). I dug out my AGMA Gear Design Handbook and put together the following document to lead one through the process. -- Lew

    Attached Files:

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