Machine Tools/gears Flashcards
A ____ is a disc, wheel or cone that has drive teeth that are meshed, or interlocked, with a mating gear
Gear
A ___ is a straight gear or a gear without a curve. Combined with a gear it converts between rotary and linear motion
Rack
5 inherent disadvantages of gears when compared to belt and chain power transmissions
-expensive
-relatively heavy
-require more exact center distance
-require more maintenance (ie backlash, lube, alignment
-has no inherent overload protection
4 general categories of gears
-spur
-helixal
-bevel
-worm
Considered to be the most basic a of gears and are most likely to be produced on general machine shop equipment
External spur gear
The teeth on an ____ are arranged around the inside dia of a hollow cylinder. Although more difficult to cut, the teeth have more contact area and the shafts can be mich closer together
Internal spur gear
Teeth on a ___ are cut at an angle to the gear axis, in a shape of a helicopter or 3 dimensional curve like a spring
Helical gear
Helical gears can operate at higher speeds with less vibration. Able to transmit larger loads than spur gears of the same diameter. T or f?
True
The teeth on a LH helical gear slope down to the left and RH slope down to the right. T or f?
True
Teeth of ___ are similar to the teeth of spur and helical gears, buy theu are formed on a surface of a cone instead of a cylinder.
Bevel gears
Bevel gears are used to transmit power between intersecting shafts, this allows the transmission of power around corners. T or f
True
Bevel gears that meet at 90 and have the same # of teeth are called
Mitre gears
Bevel gears that meet at ant angle other than 90 are called
Angular bevel gear
4 styles of bevel gears
Straight
Spiral
Zero
Hypoid
A _____ drive consists if a special threaded driver called a worm that drives a gear called worm gear or worm wheel
Worm gear
Worm gear drives connect crossing shafts at 90’ and are always used as reduction units, t or f?
True
The line of action on 2 gears that are in mesh crosses a line tangent to the pitch circles of 2bgears at an angle forming the ____?
Pressure angle
Most common pressure angles in use today are…?
14.5, 20 and 25deg
This pressure angle are sometimes described as obsolete but can still be found in lots of older equipment
14.5deg
This pressure angle hear tend to he the most popular choice for new designs
20deg
This pressure angle gears are generally used where increased strength or less undercutting is required
25deg
Minimum # of teeth in 3 pressure angles
14.5deg = 32min teeth
20deg= 18
25deg= 12
A ___ is a series of 2 or more gears in mesh
Gear train
3 types of gears in a gear train
-driver gear
-driven gear
-idler gear