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Gear Design

Discussion in 'Using Alibre Design' started by Jake_Steidy, Mar 12, 2020.

  1. Jake_Steidy

    Jake_Steidy Member

    Hello All,

    I am trying to design multiple gears in Alibre that will be 3D printed and used with several purchased gears. I was wondering if anyone has any more current experience with gear design templates or anything of the nature. I have been using the two gear design templates from this thread [https://www.alibreforum.com/forum/index.php?threads/number-of-teeth-on-gear.19578/], but I do not think either one has all the required parameters to properly create a gear. When I try to create an assembly with a McMaster 3D download the teeth do not align nicely with the gears I produce from those templates. Any and all advice and help is much appreciated.

    Thanks for your time.
  2. DavidJ

    DavidJ Alibre Super User Staff Member

    One point to consider (others may comment on its significance for downloads from McMaster) - many available 3D models that can be downloaded from the web are deliberately not quite correct. The reason being that manufacturers want to make it easy for you to design using their products, they don't want to make it easy for you to copy those products. I can well imagine that tooth form might not be exactly reproduced in the available 3D models.
    Jake_Steidy likes this.
  3. Jake_Steidy

    Jake_Steidy Member

    Thanks David I will keep that in mind, for this and future 3D model use!

    If anyone can provide their opinion on how complete the two gear design templates are I think that may also be beneficial. Like if there are specific parameters in the design that aren't accurate or anything of that nature.

  4. idslk

    idslk Alibre Super User

    Hello Jacob,

    have you tried the Gear Example?

    Jake_Steidy likes this.
  5. JST

    JST Alibre Super User

    You can generate the involute for the size required, then add clearance below the dedendum circle, and add whatever backlash allowance is needed.

    Following the Browne and Sharp series of 8 cutters is as good as you may need to get. Each is best for the lowest tooth count in the range.
  6. Lew_Merrick

    Lew_Merrick Alibre Super User

    Hi Jacob -- Are you talking about standard involute gear or are you dealing with Pinion involute fears? The relative involute pattern of a (relatively) small Pinion requires that the "inside the Pitch Diameter" of a Pinion be "undercut" to work properly -- a not insignificant advantage to Hobbing gear. -- Lew
  7. Jake_Steidy

    Jake_Steidy Member

    Hey Lew:

    I am dealing with standard involute gears to the best of my knowledge. The problem I was having was with the MMC files having large undercuts, but from your explanation that is because they have very small teeth counts(n=12;18) and are small gears (<2" Diameter). Do you see a problem with running a standard involute gear that is 3D printed with a gear that has an undercut? There is negligible force being transmitted between the gears as the gear being driven is basically free spinning with near 0 resistance.


    Thanks for that script! I was able to get it running and was able to create some gears that are just what I needed.


    I understand your first part, but am unfamiliar with the reference to the Browne and Sharp series cutters you made.

    Thank you everyone for all of your wisdom and help!
  8. JST

    JST Alibre Super User

    The point of the undercut is that it WILL run correctly with any other gear of the pitch. Without the undercut, it does not.

    The B&S series is a series of 8 cutters that cover the range from 12 tooth to a rack. Each covers a range to an "acceptable degree", and they will all work together properly. One covers from 135t to a rack, the next from 55t to 134t, and so on. IIRC the smallest toothcount is only for 12 and 13, then 14-16, then 17-20 etc.

    I was thinking that if you were modeling gears "semi-exactly", that selecting the lowest numbers of those series, such as 12, 14, or 55, etc, you would only need to model the tooth form for at most 8 sizes to cover the entire range in any pitch with an acceptable accuracy for general purposes.
    Jake_Steidy likes this.
  9. albie0803

    albie0803 Alibre Super User

    If you like I can generate involute spur gear tooth files as DXFs for you using a program called gearCAD. They are a series of lines that make up the shape. What I do is make them references and then run a spline along them to get a smooth tooth face and then pattern it as many times as there are teeth in the wheel.

    I need to know the gear type (CP/DP/M) and the number of teeth and the centre distance you want them to run at and the amount of backlash.
    VoltsAndBolts and Jake_Steidy like this.
  10. Lew_Merrick

    Lew_Merrick Alibre Super User

    Hi Jacob -- Back in the dark ages when I was learning to make gear hobs. There was an equatioin relating the number of teeth on the drive gear and pinion to their Pitch Diameters and Contact Angle that determined the need for and size of an undercut. I have not been able to lay my hands on that equation this afternoon. Sorry, -- Lew
  11. Jake_Steidy

    Jake_Steidy Member

    Hello Gentlemen,

    Sorry for the slow response, but I was able to design the gears successfully. I currently have them 3D printing and will be able to report back on my experience and how well the gears turn out based upon the printing.

    Thank you all for your kind offers, and the knowledge you've provided.

  12. Lew_Merrick

    Lew_Merrick Alibre Super User

    OK, I had to 're-write" the paper I could not find. Here it is. -- Lew

    Attached Files:

    Jake_Steidy likes this.
  13. Jake_Steidy

    Jake_Steidy Member

    Awesome resource Lew!

    This might be useful on several other new threads containing gear design. Maybe you'd want to post it on those threads as well.

  14. Lew_Merrick

    Lew_Merrick Alibre Super User

    Hi Jacob -- Actually I have a much more general and detailed document on Gear Train Design, but I am waiting to see some of the "promised features" as they will likely play a key role. -- Lew

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