When to use 25 degree pressure angle?
When to use 25 degree pressure angle?
(OP)
I am working on a small planetary gearbox design (5 inch ring) to transmit approximately 8 HP. I have done some gear stress calculations and found that I can decrease the gear stress by increasing the pressure angle from 20 degrees to 25 degrees. What disadvantages are associated with a 25 degree pressure angle gears? Is efficiency lower?





RE: When to use 25 degree pressure angle?
pressure angle but I assume the contact stresses
would be higher. If strength is your main criteria,
then go for it. The 25 degree pressure angles have
worked well in heavy equipment design where slow
speeds are encountered. No experience with high
speed equipment.
RE: When to use 25 degree pressure angle?
The efficiency for a 20deg vs. a 25deg pressure angle should be similar.
RE: When to use 25 degree pressure angle?
RE: When to use 25 degree pressure angle?
One significant issue is that your application is a planetary gear box. Higher pressure angles are usually easier to use in planetaries because it tends to help reduce the likelihood of involute interference in internal designs.
The higher pressure angle will increase the bearing loads as separation forces will go up.
Generally contact ratios go down as the pressure angles increase, however in cases of pinions with small numbers of teeth, undercutting may be avoided which in fact may contribute to higher contact ratios as well; - so we have to be careful not to over generalize.
Dont be afraid to go with the higher pressure angle if the bearing loada are not a big issue. I have gone as high as 54 degrees with great success!
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