How to find backlash between two spur gears

1. Apr 6, 2016

hello i have two spur gears. i would like to know the backlash that i would be getting. How can i calculate backlash?

2. Apr 6, 2016

billy_joule

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.

3. Apr 6, 2016

so i will need data from OEM

4. Apr 6, 2016

billy_joule

That or measure the gears you have.
Seeing as you have the gears, why not just do a test?

5. Apr 6, 2016

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

6. Apr 6, 2016

billy_joule

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?

7. Apr 6, 2016

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

8. Apr 6, 2016

RNickl

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.

9. Apr 6, 2016

CWatters

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.

10. Apr 7, 2016

Baluncore

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. Apr 7, 2016

CWatters

Backlash increases with gear wear so is there a warranty issue if it increases beyond the specified value within the warranty period?