WORM GEAR EFFICIENCY and VELOCITY
VELOCITY
The velocity of a worm gear or worm is the distance that any point on the pitch circle will travel in a given period of time, generally expressed in feet per minute (FPM). (See Figure 4.12)
Formula: Velocity (FPM) = Pitch Diameter (in inches) x .262 x RPM
WORM AND WORM GEAR EFFICIENCY
The worm and worm gear drive is never 100% efficient as there is always some power loss due to the friction (rubbing action) between the worm and worm gear. The following factors have an impact on the friction and, therefore, the efficiency of a drive:
• Lubrication
• Speed of worm
• Material of worm and gear
• Load
• Finish of surface on worm thread
• Accuracy of cutting worm and gear
• Lead angle of worm
See for yourself: Take a look at figure 4.12A. Note how the efficiency of a worm and worm gear drive increases as the teeth wear in.
FIGURING OUTPUT HORSEPOWER
In order to determine the actual maximum output horsepower of any worm and worm gear, you need to know:
• The maximum amount of load in horsepower from the power source
• The efficiency (in terms of a percentage) of the gears
These factors can then be applied to the following formula:
• Output horsepower = Input horsepower x efficiency
