Alb Mod Gearing Fundamentals Flashcards
Gears that are exposed to the outside environment are called:
Open gear drives
Note: used on light duty applications, or where sealing the gears is impractical or impossible
With an open gear drive system, gear wear is:
more excessive
Gear drives contained within a gearbox with a lubrication supply are:
Enclosed gear drives
Note: Have a long working life
____ are matched pairs of gears, manufactured together intended to mate with each other.
Gear sets
When two or more gears mesh or work together, they are called a:
Gear train
Between a pair of gears, the smaller gear with fewer teeth is referred to as:
pinion
With bevel and hypoid gear sets, the smaller gear is called the pinion and the larger gear is called the:
Crown or Ring gear
____ is when the input speed of the gearbox is the same as the output speed
direct drive
A gear train with a slower output speed than input speed is called a
Speed reducer
a gear train with a faster output speed than input speed is called a
Speed increaser
When a speed reduction occurs, it results in a mechanical advantage, which is an increase in
torque
A ____ has a bearing support on only one side
overhung gear or load
Note: Also known as cantalever
The general practice with overhung gears is to keep:
overhung gears very close to the bearing support
______ gears are mounted between two bearings
straddle mounted
____ gears have teeth on the inside diameter of the gear
Internal
____ gear trains have three or more shaft and four or more gears
Compound
The final ratio of a compound gear train is equal to all the ratios:
multiplied
___ is when the gear or shaft is allowed to move axially
end play
____ a bearing in a gearbox id done by giving a bearing less than zero axial clearance
Preloading
Gear wear can be caused by: (4)
- Lack of lubrication
- Abrasives
- Incorrect tooth contact
- Heavy loads
A ____ exists when one gear or shaft is allowed to move axially to its best position
floating gear or shaft
Gears that have a helix angle can be either:
Right or left handed
In worm and worm wheel gearboxes, the worm is:
smaller gear that looks like a screw thread
The ___ is the side in contact with the other gear teeth while torque is applied. The other side is called the coast side
drive side
The ____ is the radial distance from the pitch circle to the top land of the tooth
addendum
the ____ is the radial distance from the pitch circle to the bottom land of the tooth.
dedendum
addendum + clearance
The ___ is the total height of the whole tooth, addendum + dedendum
Whole depth
___ is the depth that the gear tooth extends toward the root of the mating tooth while in full mesh
Working depth
___ is the space between the bottom land of one tooth and the top land of the meshing gear
Clearance
The ____ is the maximum diameter at the top land of the gear teeth
Outside gear diameter
____ is the distance from the center of one tooth to the center of the next tooth at the pitch circle
Circular pitch or gear pitch
The pitch circle is located, approximately:
in the middle of the gear teeth
The ____ of a tooth is the contact part of the tooth on the addendum
Face
____ is the contact part of the tooth below the pitch circle including fillet
tooth flank
____ is the distance from one side of the tooth to the opposite side
face width
____ is the distance of the gear tooth at the pitch circle
chordal thickness
Indicates tooth strength
Crowning a gear tooth is cutting a slight curve on the face of the tooth from side to side. The purpose is to:
Prevent highly concentrated loads on the ends or edges of the gear teeth that could cause the teeth to fracture
The ____ is the angle between the line of action and a line tangent to the pitch circles
Pressure angle
The angle of a tooth from the shaft axis is the:
helix angle
Helix angles can be right or left handed. They lead to smoother tooth action, but have: (2)
- More sliding friction
- Greater axial thrust
A ___ is the term that describes the number of thread starts on a worm
start
The more starts a worm has, the ____ the worm wheel advances per turn
Faster
The face of the tooth on many gears has a radius across the flank and the face of the tooth. This is referred to as an:
Involute profile.
Note: Makes meshing of gears quieter and smoother
___ is the clearance between gears at the pitch line. Half is cut into each gear.
Backlash
____ is the ratio between the number of teeth on a gear and the pitch diameter. Indicates tooth size.
Diametral pitch
When reading diametral pitch, the smaller the number, the ___ the tooth size
larger
lack of blacklash, incorrect center distance, gear center out of tolerance, bent shafts and thermal expansion can all cause:
Binding
The ____ is the angle of the gear tooth
pressure angle
The two most common pressure angles are 14.5° and 20°. Which one is stronger?
20°. Tooth is wider at the base
If a gear set has:
- Same diametral pitch
- same pressure angle
- correct hand of gear
- shafts in correct position
- same helix angle
The gears will have proper:
Mesh
Gear teeth can have one of two profiles:
Involute or straight
An involute profile has a ____ on the face of the gear teeth
slight curve
Straight cut teeth are:
Very noisy
Note: Also not suitable for high speed or high power applications
When an even number of gears are in mesh, the last gear rotates ___ the drive gear
opposite
An __________ has both gears moving in the same direction
Internal gear set
____ gears are between the drive and driven gear. they have no effect on the gear ratio, but can change the rotation, and connect gears with a greater center to center distance.
Idler gears
If a gearbox is a speed increaser, ratios are numberically:
Less than one.
0.50:1, often called overdrives
When measuring the torque on a gear, the effective lever length is equal to the:
Radius of the gear
What are the three basic positions used to properly mesh gears? (3)
- Parallel
- Intersecting
- Crossing over at 90°
These gears were one of the first developed. Teeth are cut parallel to the shaft axis. Only suitable for shafts that are parallel. No axial thrust, unless misaligned. Easy to manufacture. Sliding and rolling action, but the power transfer happens over a rolling action.
Spur gear,
Note: Can be used in 3 arrangements, internal, external and rack and pinion.
These gears have their teeth cut at an angle to the shafts axis. They are stronger and have more teeth in contact than a spur gear. Can be used in a single or double setup, to help eliminate thrust loads. When used in parallel, opposite hand helix angles are used. When crossing over at 90, same hands are used.
Helical gears
Most common helix angles are 7 to 23°. Greater the angle, more teeth are in contact, more thrust
These gears are similar to double cut helical gears, except the teeth form a point in the center of the gear. Cancels out thrust loads. High speed heavy load applications.
Herringbone gears
These gears are used on shafts that have intersecting axis. Most commonly cut at a 90° angle, but can intersect at other angles. Develop both axial and radial loads. Can be straddle mounted or overhung. Teeth can be straight or curved.
Bevel gears.
These are bevel gears, but have a 1:1 ratio.
Mitre gear
This is the simplest bevel gear, teeth are straight but tapered to compensate for the smaller inside tooth diameter. Noisy and rough, do not have a high torque capacity
Straight bevel gears
These bevel gears have curved teeth that are angular to the shaft axis. Stronger, have a smoother transfer of power, more teeth in contact. Manufactured in pairs. Gears must be in opposite hand. Generate a thrust load
Spiral bevel gears
These bevel gears have teeth cut similar to straight bevel gears, but the teeth are curved. Teeth do not cut at an angle. Are smoother and quieter than straight cut. Does not generate a thrust load.
Zerol bevel gears
When gears are too close together, clearance is insufficient, gears are noisy and will bind and wear. If there is excessive clearance:
Cannot transfer rated load, may be noisy
