Ring gear backlash

[TerryR1]

How do I apply the AGMA recommended backlash to ring gears?

Specifically:
I have a 92" PD ring gear and a 18" PD pinion. DP=1.
If I go by radius1-radius2 (actual center distance), the AGMA table recommends 0.040-0.060.
If I go by radius1+radius2 (spur gear center distance), the AGMA table recommends 0.060-0.080.
I prefer 0.060-0.080, but need to make sure it is the right choice and supported by AGMA or similar.

Anyone know? Please provide a reference. Thanks!

 

[israelkk]

To what AGMA document number and version are you referring?

 

[TerryR1]

It's in my machinery's handbook. Also here on the web:

http://www.engineersedge.com/gears/determining_gear_backlash.htm

 

[israelkk]

Backlash values for meshed gears are recommendation only and are not mandatory in AGMA. Read the explanation following the table in the Machinery's Handbook.

 

[TerryR1]

True... I'd just like to know how to best apply that table to ring gears with internal teeth. Seems strange to have to have less backlash the larger the pinions get.

 

[dinjin]

It makes sense to me to base it on CD if you are simply looking at expansion between the two gears. If the internal gear expands it will open up the backlash whereas if it were external it would tend to close the backlash.
Thanks for bringing this up. I have not seen it questioned before.

 

[tbuelna]

TerryR1,

The document I have suggests a backlash of .040 to .060 inch for a 37" center distance and 1.0 DP gears.

If your gear mesh only drives in one direction, then tight backlash control is generally not an issue. A pinion and internal ring gear combination also has a high contact ratio by nature, which also makes it less backlash sensitive.

Just make sure you have enough backlash to prevent the tooth trailing flanks from contacting under all conditions of thermal expansion, deflection and tooth geometry errors.

I'd also make one other suggestion. If you haven't done so already, you might want to make adjustments to your geometries to equalize both mesh contact sliding and tooth bending strength with an 18T pinion and 92T internal ring gear combination. It would improve efficiency and load capacity.

Hope that was helpful.
Terry

 

[dinjin]

I too like tbuelna's suggestion about using an enlarged
pinion if the pinion is always the driver. Using a 17 tooth pinion on the 18 tooth blank works very well for many internal gear applications. You could then use the same CD as the 18 tooth pinion 92 gear arrangement.
The only thing not discussed was if the quality of the gears were agma 6 or of lesser quality, you might want to open the backlash up a little to allow for the greater eccentricity of the gears.
If you are confined to that particular gear ratio, then a long and short addendum arrangement also works well.