NEW Machinist 3 > Gears > Flashcards

Gears Flashcards

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1
Q

4 general categories of gears

A

-Spur

-helical

-bevel

-worm

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2
Q

A __ is a disc, wheel or cone that has drive teeth that are messed, or interlocked with a mating gear

A

Gear

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3
Q

A __ is a straight gear or a gear without a curve

A

Rack

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4
Q

A gear is used to transmit rotary motion. A gear and rack combination converts between rotary and linear motion. T or f?

A

True

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5
Q

Gears are used to

A

-transmit power
-increase/decrease torque
-increase/decrease speed
-maintain exact speed ratios
-change direction of rotations
-synchronize drives

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6
Q

Inherent disadvantages of gears

A

-relatively expensive
- heavy
-requires exact center distances
- requires maintenance
-have no overload protection

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7
Q

___ are the most basic of gears and are the most likely to be produced on general machine shop equipment

A

External spur gears

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8
Q

__ gears are used for low to moderate speed applications. At higher speed these gears tend to make noise and vibration

A

Spur gears

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9
Q

The teeth on an __ are arranged around the inside diameter of a hollow cylinder

A

Internal spur gear

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10
Q

The teeth on a __ are cut along a straight surface

A

Rack

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11
Q

The teeth on a __ are cut at an angle to the gear axis or 3 dimensional curve like a spring

A

Helical gear

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12
Q

The meshing action of __ gear is smoother than of spur gears, allowing it to operate at higher speeds with less vibration. It can transmit larger loads than spir gears of the same diameter

A

Helical gears

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13
Q
A
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14
Q

Helical gears may be made with a left hand or right hand helix. When looking at the gear if the gear slopes down to the left then it is LH, and RH if sloping to the right. T or f?

A

True

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15
Q

The teeth of __gears are like the teeth of spur and helical gears but they are formed on the surface of a cone instead of a cylinder

A

Bevel gears

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16
Q

__ gears are used to transmit power between intersecting shafts. This allows the transmission of power around corners. Most shafts intersect at 90deg and some are at angles other than 90deg

A

Bevel gear

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17
Q

Bevel gears that meet at 90deg and have the same # of teeth are called __?

A

Mitre gears

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18
Q

Bevel gears that meet at any angle other than 90deg are called __?

A

Angular bevel gears

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19
Q

A __ gear drive consists of a special threaded driver called a worm that drives a gear called a worm gear or worm wheel

A

Worm gear

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20
Q

Worm gears drives connect crossing shafts at 90deg and are always used as reduction units. Can provide large mechanical advantages or speed reduction in compact space but they are less efficient than other gear systems, t or f?

A

True

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21
Q

When two gears are in mesh, power is transferred from one gear to another along a theoretical path called the __?

A

Line of action

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22
Q

The line of action crosses a line tangent to the pitch circles of 2 gears at an angle forming the __?

A

Pressure angle

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23
Q

Gear teeth with lower pressure angles have smoother and more efficient power transmission and create less radial or separating force, t or f?

A

True

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24
Q

Gear teeth with higher pressure angles are stronger than ones with lower presser angles, t or f?

A

True

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25
3 most common pressure angles that are used today
14.5deg- sometimes described as obsolete. Used in older equipment 20deg- most popular for new designs 25deg- used where increased strength or less undercutting is required
26
Minimum # of teeth on gears with the 3 different pressure angles are
14.5 = 32 20 = 18 25 = 12
27
For 2 gears to mesh correctly, they must be of thr same pressure angle, t or f?
True
28
Power is transferred by the gears through a __? It is a series of 2 or more gears in mesh. The gears must have thr same tooth size, pressure angle and type of gear
Gear train
29
3 types of gears in a gear train
-driver gear - driven gear -idler gear
30
A __ gear imparts power to the gear train. It is the first gear in a simpler gear train and is connected to the driving shaft. The initial drive gear of a system is often referred to as the pinion, particularly in the case of speed reducers
Driver gear
31
A __ gear recieves power from a driver gear. Is it the last gear in a simple gear train and is connected to the driven shaft
Driven gear
32
__ gears lie between the driver and the driven gears and have no effect on the ratio of the gear train. The purpose of it is to span distance, reverse direction of rotation or provide means to adjust backlash
Idler gear
33
__ gear trains have 1 driver and 1 driven gear and they may or may not include idler gears. All gears are arranged on the same plane
Simple gear train
34
Simple gears trains have one reduction stage and are referred to as __?
Single reduction trains
35
__ gear trains have atleast 2 driven and driver gears and they may or may not include idler gears.
Compound gear train
36
When 2 external gears are in mesh, they rotate in opposite directions. When 2 gears are mounted on the same shaft they rotate in the same direction. T or f?
True
37
As a rule of thumb, if the number of shafts is odd, the first and last gear rotates in the same direction. When it is even number of shafts, the first and last gear rotate in opposite direction, t or f?
True
38
What does VR and MA stand for when cutting gears
Velocity ratio Mechanical advantage
39
VR is equal to ?
Mechanical advantage
40
Do you ignore idler gears when calculating the ratio of a gear train? Y or n?
Yes. Treat the forst and last gear as if they were in mesh with each other
41
The __ of a gear is the distance from a point on one tooth to a corresponding point on the next tooth. Measured on the pitch circle
Circular pitch
42
The __ is the radial distance from the root of the gear tooth to the pitch circle. It is larger then the addendum by an amount equal to the clearance
Dedendum
43
The __ of a gear tooth is the contact or working surface of the gear tooth between the pitch circle and the top of the tooth
Face
44
The __ of a gear tooth is the surface of the tooth that lies between the pitch circle and the root circle of the gear
Flank
45
The __ depth or __ depth is the radial distance between the OD and root diameter. It is equal to the sum of the addendum and dedendum. Represents the depth that a cutting tool entere into the gear blank
Full depth whole depth
46
For metric gears the __ of a gear describes the size of the gear tooth. It is equal to the pitch diameter of the gear divided by the # of teeth on the gear
Module
47
The __ of a gear is the diameter of the outside circle or thr circle that passes through the tops of the gear teeth. It is the diameter the gear blank is made prior to cutting gear teeth
Outside diameter or OD
48
The __ of a gear is the effective diameter of the gear where all ratios and speed calculations are made. It is the diameter where the tooth of the gear and space between teeth are of equal thickness.
Pitch diameter
49
The __ of a gear is the circle that passes through the roots of a gear teeth. It represents the minor diameter of a gear
Root circle
50
The __ of a gear tooth is the length of the arc that describes the thickness of the gear tooth along the pitch circle
Thickness
51
In the imperial system, the __ of a gear describes the size of the gear tooth. It is the ratio of the # of teeth on the gear to the # of inches of pitch diameter
Diametral pitch
52
The term __ applies to gear racks. It is the distance from a point on 1 tooth to the same point next tooth. It is equal to the circular pitch of a mating gear
Linear pitch
53
54
The __ of a gear tooth is the radial distance from the pitch circle to the outside circle or major diameter of the gear
Addendum
55
The __ addendum is the radial distance from the outside of the diameter of a gear tooth the chord that contacts the pitch circle on both flanks of a tooth
Choral addnedum
56
The __ thickness is the length of the chord that is used to define chordal addendum
Chordal thickness
57
The __ depth is the radial distance that a gear tooth extends into the space of a mating gear at full engagement. It is equal to 2x the addendum
Working depth
58
The __ is the radial distance from the top of a fully engaged gear tooth to the root circle of a mating gear. It is provided to ensure that top of the tooth does not contact the mating gear during operation
Clearance
59
The __ distance between a pair of mating gears is the distance between the axes of the gears
Center distance
60
The __ angle of a gear is the angle formed by a line through the point of contact of the 2 mating teeth and tangent to the 2 base circles. For 2 gears to mesh correctly they must have the same of this
Pressure angle
61
A __ is a milling machine accessory that allows precise rotation of a workpiece. It consists of a spindle that is mounted in a housing and connected to a crank handle
Dividing head
62
You can control how much the crank handle rotates with the use of a __, which is a circular plate with a series of hole circles
Hole plate
63
Use a __ to ensure that the rotation of the gear is synchronized with the rotation of the dividing head spindle
Drive dog
64
You may use a __ caliper to measure chordal thickness of a gear tooth at the chordal addendum
Gear tooth caliper
65
The teeth on __ gears are arranged on the face of a cone and they taper from one end to the other. They transmit motion between non parallel shafts
Bevel
66
4 types of bevel gears
-straight -spiral -zerol -hypoir
67
The teeth on __ bevel gears are straight and point directly at the apex of the cone. They taper from one end to the other and have an involite tooth form. They have 20deg pressure angle
Straight bevel gear
68
69
Straight bevel gears are the most common type of bevel gear and have many of the same advantages as a spur gear. They are the only bevel gear that can be cut on your standard milling machine, t or f
True
70
71
The teeth on a __ bevel gears are curved and set at an angle to the axis of the gear. The depth of the tooth space can be parallel or tapered depending on how the gear is manufactured
Spiral bevel gear
72
The spiral angle on a spiral bevel gear is measured at the mid point and is often 35deg. Can also rotate at peripheral speeds higher than 8000fpm. T or f?
True
73
__ bevel gears incorporate the best features of straight and spiral bevel gears and they may be thought of as a compromise between the 2. The teeth are curved like those on a spiral but they have no spiral angle
Zero bevel gear
74
Zerol bevel gears are most useful in precise applications in which backlash must be kept to a minimum such as instrumentation. Shouldn't be used at peripheral speed higher than 1000fpm. T or f
True
75
__ bevel gears differ from other bevel gears in that their shafts do not intersect, but are offset instead. Although they are the most difficult to manufacture, they offer significant advantages that more than compensate for their higher cost
Hypoid bevel gear
76
Advantages of hypoid bevel gears
Strength Higher ratios Sliding action
77
The most useful place to start when designing any gear is the pitch diameter. It is the starting point for almost everything else, t or f?
True
78
The pitch diameter of a bevel gear is measured at the large end of the cone. The circle defined by the pitch diameter is called the __?
Pitch circle
79
The teeth on a bevel hear are arranged around a cone. Contact beteren bevel gears occurs on a cone called _6?
Pitch cone
80
The crest on the teeth on a bevel gear is called__ and the roots of thr teeth that form the --
Face cone Root cone
81
The __ is the angle between the face of the blank and the axis of the gear. It must be calculated before turning the blanks
Face angle
82
The __ angle is the angle that the dividing head must be set to when milling a bevel hear
Root angle
83
The __ diameter of a bevel gear is the diameter at the crown
Outside diameter
84
What type of bevel gear has the strongest tooth
Hypoid
85
__ gears differ in design from spur gears in the orientation of their teeth.
86
The NDP is always a larger number than the DP, as the gear tooth profile is always smaller normal to the helix than in the plane of the gear, t or f?
True
87
The __ of tooth helix is the distance it would take for one tooth of a helical gear to wind completely around the circumference of a helical gear and return to the same start angle
Lead of tooth helix
88
The __ of a helical gear is the angle formed by the intersection of the straightener helix with the axis of the workpiece
Helix angle
89
The __ circular pitch is the distance measured on the pitch circle, normal to the tooth face, from a point on one gear tooth to the corresponding point on an adjacent gear tooth
Normal circular pitch
90
The __ circular thickness is the thickness of the gear tooth, measured on the pitch circle, normal toxthe tooth face
Normal circular thickness
91
__ gears are most often compared to spur gears and used in similar applications such as transmission of power between parallel shafts. They are found in mechanical devices such as automobile transmission, industrial machines and even toys
Helical gears
92
Advantages of helical gears compared to spur gears
- more quiet and less vibration - able to transmit more power than a spur gear of same size - capable of operating at higher speeds. About 2/3 faster than spur gears - center distances may be adjusted
93
Disadvantages of helical gears compared to spur gears
- more complex and expensive to manufacture -transmits power less efficiently and generates more heat -generate axial thrust
94
All gears are defined by 3 basic elements, there are
-number of teeth N - size of tooth (DP, CP or module) - pressure angle
95
A 20deg pressure angle spur gear of the same OD and N has less undercut at the base of the tooth than a 14.5deg pressure angle gear, resulting in a stronger gear. T or f
True
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