Generate spur gears 3:1 ratio with setting pitch diameter and number of teeth

[roygoldray]

Hello,

I'm trying to figure out, how to generate gears like this example, where I have 9 to 27 teeth with a ratio of 3:1 and the small gear pitch diameter must be 15 mm:

I've kept Center Distance and selected a 3.500 ul, Diameter Pitch that does give an error above 10.0000 ul/in, a minimal number of teeth without calculation error is 22, center distance in the result is too big 115.570 mm.

As a result, I had to find the actual center's distance, according to the required size and ratio, and also use a big gear as a driver.

Would be helpful to get some guidance on how to solve this task.

[swalton]

Its been years since I have gotten into the details of gear design, but I'll give this a shot. 

Are you working with US Customary or Metric units?  Typically metric gears are governed by Module, not Diametral Pitch.  I'm confused because you are mixing Metric linear dimensions with US Customary gear terms.

Are you buying the gears or manufacturing them yourself?  If you are buying them, then you need to select a DP or Module that is commercially available.  If you are manufacturing them, why aren't you using dedicated gear design software like KISSsoft?  The 3d models produced by the Inventor Gear Component Generator have a simplified tooth form and are not true involutes and should not be used for precision fabrication.  3D printing might be ok, injection molding based on the Inventor 3d models will have poor results.

A 15 mm pitch diameter is 0.5905511811 inches.  If you chose a 24 DP, 14 tooth pinion, you get a pitch diameter of 0.5830 in or 14.8082 mm.  That seems close enough.  See http://shop.sdp-si.com/catalog/product/?id=A_1T_2-Y24014

3:1 ratio would require a 42 tooth driven gear or a 1.7500 in pitch diameter.  (0.5830+1.7500)/2=1.1665 in or 29.6291 mm shaft centers.  See http://shop.sdp-si.com/catalog/product/?id=A_1T_2-Y24042

You did not show the Calculation tab of the Component Generator, so I don't know if the Acetal gears I linked will carry your design loads/speeds.  Note that the Component Generator only lists Steel/Iron materials.  You will have to find the proper mechanical properties if you are using different materials to fabricate your gears and want accurate life predictions. 

I expect you will have to check several different combinations of tooth size (DP or Module), material, and allowable center distance to close the design problem.  Don't forget to adjust your center distance to allow some backlash between the gears to accommodate manufacturing tolerances, thermal expansion and wear.

[roygoldray]

Hello, 

Thank you for your feedback and answer

I am new to Gear design. It looks like I'm using Metric units in assembly, now I'm trying to find this setting for Spur Gear Component Generator:

It will be 3d printed gears with PLA or nylon with 3:1 ratio, 15 mm of pitch diameter for small gear, and also I have to try maybe 10 mm of pitch diameter as well if it is possible to minimalize center distance.

The goal is to accelerate the rotation of 51 grams part on the small driven gear, when the big driver gear motor rotates 0.07 sec 60°, covering 120° of the control angle to convert 120° on the big gear to 270° on the small. 

I've to figure out with calculation and setting of the Spur Gear Component Generator. I'm trying to figure out, how to make gear size with the same settings 44 and 14 mm::

Also, I've tried to create platform models with a 29.6291 mm shaft centers distance:

As a result, I got errors, and I've tried 30 mm shaft centers distance with discs ⌀ 15 mm and ⌀ 45 mm: