How to find backlash between two spur gears

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Discussion Overview

The discussion revolves around calculating the backlash between two spur gears, focusing on methods for measurement and considerations for design specifications. Participants explore both theoretical and practical approaches to understanding and quantifying backlash in gear systems.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • Some participants suggest that full engineering drawings are necessary to determine backlash, considering angular play and axis tolerances.
  • Others propose measuring the gears directly as a practical approach to finding backlash.
  • One participant describes a method involving locking one gear and using a dial gauge to measure angular play.
  • Another participant discusses a design approach to eliminate backlash by using two large gears on one shaft with a spring mechanism.
  • A technical calculation is presented that relates backlash to the difference in axial separation of the gears, incorporating the contact angle.
  • Concerns are raised about the impact of gear wear on backlash and potential warranty implications.

Areas of Agreement / Disagreement

Participants express various methods and considerations for measuring and managing backlash, but no consensus is reached on a single approach or solution. Multiple competing views remain regarding the best practices for calculating and addressing backlash in gear systems.

Contextual Notes

Limitations include the need for specific data from OEMs, the dependence on precise measurements, and the potential variability introduced by gear wear over time.

Who May Find This Useful

Individuals involved in mechanical design, particularly in applications involving gears, as well as those interested in the practical aspects of gear measurement and design specifications.

Shady99
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hello i have two spur gears. i would like to know the backlash that i would be getting. How can i calculate backlash?
 
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My guess; You'd need full engineering drawings, find the angular play the tolerance stack up on the meshing teeth will cause. You'll also need to know the axis to axis tolerance.
 
billy_joule said:
My guess; You'd need full engineering drawings, find the angular play the tolerance stack up on the meshing teeth will cause. You'll also need to know the axis to axis tolerance.
so i will need data from OEM
 
That or measure the gears you have.
Seeing as you have the gears, why not just do a test?
 
billy_joule said:
That or measure the gears you have.
Seeing as you have the gears, why not just do a test?
how can i measure the angular play?...gears are small like one is 80mm pitch diameter and the other is 247mm pitch of 1 module and 20 deg pressure angle
 
I'd lock the small gear, set a dial gauge on the large gear, near the OD and rock it back and fourth.
Why do you need to know anyway?
 
billy_joule said:
I'd lock the small gear, set a dial gauge on the large gear, near the OD and rock it back and fourth.
Why do you need to know anyway?
i am designing a turntable. i want to know the backlash so i can mention it in its design specs i.e. the system has this much backlash ,so that the end user knows it
 
An audio turn table?
Gears can/will produce a lot of noise. Any reason you're going with gears over the proven belt drive?

Ignore me if it's not audio related.
 
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You can design out backlash. One way is to have two large gears on the one shaft, one fixed to the shaft and one free to rotate. A spring is fitted to rotate one relative to the other. The spring is compressed slightly before both gears are meshed with the smaller gear on the other shaft.
 
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  • #10
If the contact angle is 20°, then one tooth is really a 40° wedge.
Hold the gears against each other. Measure the axial separation, Sclose. Then mount the gears in the final environment and again measure the axial separation, Sfar. Compute dS = Sfar - Sclose.
The backlash is proportional to the difference in separation, dS.
The coefficient of proportionality is Tan( 40° ) = 0.839
Backlash = dS * Tan( 40° )
 
  • #11
Backlash increases with gear wear so is there a warranty issue if it increases beyond the specified value within the warranty period?
 

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