Gears Flashcards
What are gears used for?
To transmit force and motion (rotary or linear)
What do gears do?
Connect shafts by using a gear train, reduce speed and increase torque by using a reduction unit, increase speed by using an overdrive unit
Where is the pitch line in a gear?
The pitch line is the line of contact between the two cylinders
What does addendum (add) stand for?
The part of a tooth that lies between the pitch circle and the outside diameter of a gear
Define Dedendum( ded)
The part of the tooth that lies between the pitch circle and the root diameter of a gear
Define Clearance (cl)
The gap between the working depth and the whole depth
Define circular pitch
The distance between two corresponding points on adjacent teeth, measured on the pitch circle
Define outside diameter (Od)
The total number of teeth on the gear divided by the pitch diameter in inches
Pitch diameter (Pd)
The diameter of the pitch circle
Working depth (wkd)
The depth of a tooth engagement of two meshing gear teeth
Whole depth (whd)
The total height of a tooth or the total depth of a tooth space
Chordal thickness (tooth tickness)
The thickness of the tooth (at the pitch circle) on the face of the gear
What are the two most common pressure angles?
14.5° and 20°
What is pressure angle?
In the angle of gear tooth
Spur gear
External Spur gear
Internal Spur gear
Rack and pinion
Single helical gear
Double helical gears
Herring bore gear
Bevel gear
Hyped gear
Worm gear
What is direct drive?
When input speed of the gearbox is same as output speed
Drive gear is
The input gear of the gear train that turns the mating gear
Driver gear is
Output gear in the gear train that the drive gear forces to turn
Speed reducer is-
A gear train with a slower output speed than input
What are examples of gear wear?
Lack of lubrication
Abrasives in the gear train
Incorrect tooth contact
Extended heavy loads
What is backlash
The clearance between the gear teeth at the pitch line approximately halfway up the tooth face
What does backlash do?
Keeps teeth from binding and allows room for thermal expansion and for a lubricating film
What do gears need to mesh correctly?
Same diametral pitch
Same pressure angle of gear teeth
Correct hand of gear (unless they are straight teeth)
Shafts in correct position
Same helix angle
What is an idler gear?
Change the direction of rotation or keep it the same (doesn’t effect gear ratio)
Three parts of a sun gear
Ring gear, Sun gear, carrier with mounted planet gears
Methods of checking gear meshing?
Prussian blue
Venétain red (orange paste)
Black light
Pencil lead
How to check backlash?
Dial indicator
Lead wire (deformed between teeth)
Using feeler gages manually fitted between mating gears)
When checking blashlash what must you ensure?
Components parts are clean
