Spur Gear Ratio: Optimal Ratio Explained

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Discussion Overview

The discussion revolves around the concept of optimal spur gear ratios, exploring what constitutes an optimal ratio for various applications. Participants provide insights into the selection criteria and mathematical considerations involved in determining these ratios.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant defines the optimal spur gear ratio as the ratio that best meets the needs of the application, suggesting that the term "optimal" should be carefully considered.
  • Another participant suggests a specific ratio of about 6.5 to 1 without further context.
  • A different contribution states that a typical spur gear ratio ranges from 1:1 to 1:6, with a maximum pitch line velocity of 25 m/s, and mentions the minimum number of teeth for a gear with a normal pressure angle of 20 degrees.
  • Participants discuss the preferred number of teeth for spur gears, listing a range of values that may be optimal for different applications.
  • It is noted that the p/q ratio of gear teeth should consist of integers that do not share common factors to ensure even wear and a "hunting tooth" effect.

Areas of Agreement / Disagreement

Participants express differing views on what constitutes an optimal spur gear ratio, with no consensus reached on a specific value or criteria for determining optimality.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about applications and the specific contexts in which these ratios are deemed optimal. The mathematical steps and definitions of "optimal" are not fully resolved.

failedengineer
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TL;DR
Single stage spur gears ratio
What is an optimal spur gear ratio?
 
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The ratio that best meets the needs of the application. A good search term is the word optimal.

That answers the wrong question, then you need to more carefully word your question.
 
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About 6.5 to 1
 
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https://roymech.org/Useful_Tables/Drive/Gears.html#Design said:
A single spur gear is generally selected to have a ratio range of between 1:1 and 1:6 with a pitch line velocity up to 25 m/s. [...] The minimum number of teeth on a gear with a normal pressure angle of 20 desgrees is 18.

The preferred number of teeth are as follows
12 13 14 15 16 18 20 22 24 25 28 30 32 34 38 40 45 50 54 60
64 70 72 75 80 84 90 96 100 120 140 150 180 200 220 250
 
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The p/q ratio should involve integers p and q that do not share common factors, so the gears will wear evenly, with a "hunting tooth".
 

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