Sprockets question

I am confused that different sprocket have different difference between outer diameter and the pitch diameter, especially of the 72T. Please look at the sketch of #25 Plate Sprockets.


How could I CAD sprocket with large number of teeth, thank you!

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If you are asking what the difference is between the outer diameter, and the pitch diameter, Ii can help you with that.

The outer diameter is the edge of the part, if you were to fill in all of the “valleys” on the sprocket, and have a full circle. If you see in the drawings, it’s the outer edge of the teeth. The pitch diameter is where these chain links would mesh. It’s the same with gears. If the two pitch diameters are tangent, then the gears would not interfere (go inside) with each other, or be too far away. It’d be the goldilocks zone. So imagine the pitch diameter as an imaginary line that each gear, sprocket, pulley, etc. has, in which they have different sizes.

CADding things like this typically require precision. If you are using Solidworks, then it does have tools on the right side of the screen. You can use something called a diametral pitch to help you (not to be confused with a pitch diameter). Or in this case with #25 chain, there appears to be a pattern. But I will explain it how I see it. I’d might be able to get you a solid answer if you give me the amount of teeth you’d be looking for.

  1. Make sure that you are using the correct pitch, or distance between the teeth.
  2. Diametral pitch is important - you can’t have 50 teeth on a pitch diameter of 1.3.

Hopefully that teaches you a bit, not sure if it helps though. Good luck, and I might be back. Look into the Solidworks tools. All you would really need to do is CAD a sprocket tooth profile (you can copy it), then do a circular pattern.

image

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I’ve never caded a sprocket but from what online resources I found it’s not much harder than a pulley. https://www.instructables.com/id/How-to-Draw-a-Sprocket-Gear/

Cooking down @Radiator72’s:

  • The pitch diameter runs through the chain. Use this number for converting torque to force.
  • The outer diameter runs through the tips of the sprocket. Use this number to not hit other things.
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If your using Inventor the design tools will calculate the different values for after specifying how many teeth and type of chain you want to use.

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Solidworks has the design library, located on the right tab (three stacks emblem), and it has the same function as this. There is a motion tab that can help you with sprockets.

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You don’t need to CAD the sprocket. Vex literally has STEP files for you. @minhaonian

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If you’re using onshape, maybe this helps.

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