Is outside diameter the same as circumference?

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Discussion Overview

The discussion revolves around the concepts of outside diameter and circumference, particularly in the context of gears. Participants explore definitions, relationships between these measurements, and the specific terminology used in gear specifications.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Technical explanation

Main Points Raised

  • The original poster (OP) questions whether outside diameter is the same as circumference and seeks methods to calculate outside diameter using radius or diameter.
  • Some participants suggest that outside diameter (OD) refers specifically to the diameter of a pipe or tube, while others clarify it pertains to gears in this context.
  • One participant explains that the outside diameter of a gear is defined as the diameter at the tips of the teeth, distinguishing it from pitch diameter and root diameter.
  • Another participant notes that circumference is calculated as the outside diameter multiplied by π, emphasizing the difference between diameter and circumference.
  • There is mention of various diameters associated with gears, including base diameter and the diameter along the line of action.

Areas of Agreement / Disagreement

Participants generally agree on the definitions of outside diameter and circumference, but there is some contention regarding the specific application to gears versus other cylindrical objects like pipes. The discussion remains somewhat unresolved regarding the clarity of terminology and its implications in different contexts.

Contextual Notes

Some participants reference the need for clarity in gear specifications, indicating that different types of diameters exist for gears, which may not be universally understood without context. There is also a suggestion to consult external resources for further clarification.

bcrary3
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Okay, this might be a stupid question, but I have a sheet with all the formulas to find all kinds of anything you'd need to find about a gear. However I am confused by when it says outside diameter. Is outside diameter the same as circumference?
How do I find outside diameter using either the radius or diameter of the circle?

Thanks!
 
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bcrary3 said:
Okay, this might be a stupid question, but I have a sheet with all the formulas to find all kinds of anything you'd need to find about a gear. However I am confused by when it says outside diameter. Is outside diameter the same as circumference?
How do I find outside diameter using either the radius or diameter of the circle?

Thanks!

There is this really marvelous facility on the Internet called Google Search. You should learn how to use it. I'll bet a Google entry of define "outside diameter" will tell you what you want to know.
 
phinds said:
There is this really marvelous facility on the Internet called Google Search. You should learn how to use it. I'll bet a Google entry of define "outside diameter" will tell you what you want to know.
just as easy to also post the answer to newb Q, and then foster use of Gool or the like.

OP, no, OD is just that, the OD of say diameter of a pipe (the circular cross section after cutting the pipe perpendicular to its radial axis). mostly everything is 3D, thus a tube has a ID due to wall thickness.

Circumferene = 2πr = πd
 
the OP is asking about gears, not pipe.

Gear specifications have several different diameters, since the gear teeth are along the radius. So there's a diameter at the base of the tooth, at the outside edge of the tooth, along the line of action (where the meshing teeth touch) etc. Look at a gear manufacturer's website for a drawing and the definitions for the type of gear you're interested in.

Or try this:
https://en.wikipedia.org/wiki/Standard_pitch_diameter#Standard_pitch_diameter
 
Last edited:
my bad, didnt see the gear piece.

are they like threading guides, a minor and major diameter, w/ different designation for external vs internal threads (teeth in the case)?
 
The outside diameter of a gear is just the diameter at the tips of the teeth. They specify "outside" in order to differentiate from things like the pitch diameter and the root diameter.
 
Thanks for the help everyone! :D
 

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