Current status on recess action gears? 1

[Gearen]

Hi,
As I understand it there is an old rule about full recess action gears. If the pinion has all addendum and it is driving the gear it will run smoothly but if the gear then drives the pinion it will be much problems. This comes mostly from old books (1960 and earlier) but I haven't seen it mentioned in newer literature and don't find much in scientific articles.
I will not have full recess gears but maybe 75-90% addendum to dedendum on pinion and the gear maybe drives the pinion 20-30% of the time (hypoid axle gear).

I read this website:

http://www.csparks.com/watchmaking/CycloidalGears/RichardThoen.xhtml

where Thoen says that for involute gears this is from an old time when surface roughness and pitch errors was much bigger.

With modern machines and manufacturing, is this still an issue or can I stop worrying about the gear driving the pinion occasionally?

 

[Philrock]

A gearset that has mostly recess action for speed reduction will have mostly approach action for speed increasing. This will have significant effects on specific sliding and contact point temperature. Get some good gear analysis software and check your gearset for:

power rating for pitting resistance (wear)
power rating for tooth bending strength
contact point flash temperature

If the contact point flash temperature is higher than recommended for your lubricant, the likelihood of scoring increases.

 

[israelkk]

The issue of all recess gears is extensively covered in the book On the Geometry of External Spur Gears by T.W. Khiralls Chapter 7 page 256 to 270. Khiralla was a great advocate of these types of gears and brings examples how he solved failure of gears in machines by replacing them with all recess gears (without changing the center distance).

Quoting Khiralla "The power flow must always be from the all addendum driver to the all dedendum follower. The all dedendum gear must never be used as a driver, because this results in an all approach action gear system which will be very noisy, have a rough tooth action and be very inefficient".

Added to Philrock post, for a gear system that is used both as a speed decreasing system and speed increasing system, the gears should be designed such that the specific sliding for both types of uses is balanced and minimized.