MD - Day 7

angular gears

Are bevel gears mounted on intersecting shafts at angle of other than 90°?

crown gear

Is one in which the pitch angle is 90°, that is, the pitch cone has become a plane.

worm gear

Is used to transmit power between nonintersecting shafts, nearly always at right angle to each other.

shell and integral

The two types of construction for the worm are

20°

The standard pressure angle for fine pitch gears is __ degrees and is recommended for most applications.

1.0

The contact ratio of a pair of mating spur gears must be well over __ to insure a smooth transfer of load from one pair of teeth to the next pair.

1.4

As general rule contact ratio should not be less than about

32

Surface roughness on active profile surfaces on gear is about __ pitch.

a tensile fatigue

Tooth breakage on gear is usually a __.

American Gear Manufacturers Association

AGMA means

toughing

Which of the following does not belong to the group?

7000 fpm

Well proportion commercial gears with a pitch line velocity of less than __ will normally not score if they have a reasonably good surface finish and are properly lubricated.

10%

Experimental data from actual gear unit measurements are seldom repeatable within a plus or minus ___ band.

applied load

Pitting is a function of the Hertzian contact stresses between two cylinders and is proportional to the square root of the __.

resonance

When an excitation frequency coincides with a natural frequency.

1.5 to 2 psi

The average tooth stiffness constant of

450°F

Cast iron shall not be used over

hunting

When the number of teeth in a pair of meshing gears are such that they do not have a common divisor.

12

For internal gears having a 20° pressure angle and full depth teeth, the difference between the number of teeth in a gear and pinion should not be less than ___ .

17 teeth

Zero bevel gears of 20 degrees angle should have a pinion either no less than __ .

gear

___ are machine elements that transmit motion by means of successively engaging teeth.

addendum

Height of tooth above pitch circle or the distance between the pitch circle and the top of the tooth.

addendum circle

The circle that bounds the outer ends of the teeth

arc of action

Arc of the pitch circle through which a tooth travels from the first point of contact with the mating tooth to the pitch point

angle of recess

Is the angle through which the gear turns from the time a given pair of teeth are in contact at the pitch point until they pass out the mesh

angle of action

Is the angle through which the gear turns from the time a particular pair of teeth come into contact until they go out the contact.

angle of approach

Is the angle through which the gear turns from the time a particular pair of teeth come into contact until they are in contact at the pitch point.

arc of approach

Arc of the circle through which a tooth travels from the point of contact with the mating tooth to the pitch point

approach ratio

The ratio of the arc of approach to the arc of action.

axial plane

In a pair of gear it is the plane that contains the two axes, in a single gear, it may be any plane containing the axis and the given point.

arc of recess

Arc of the pitch circle through which a tooth travels from its contact with the mating tooth at the pitch point to the point where the contact ceases.

backlash

The amount by which the width of the tooth space exceeds the thickness of the engaging tooth on the pitch circles.

base circle

The circle from which an involute tooth is generated or developed.

helix angle

The angle, at the base cylinder of an involute gear, that the tooth makes with the gear axis.

base pitch

In an involute gear it is the pitch on the base circle or along the line of action.

normal base pitch

Is the base pitch in the normal plane.

axial base pitch

Is the base pitch in the axial plane.

center distance

The distance between the parallel axes of spur gears and parallel helical gears, or between the crossed axes of helical gears and worm gears.

central plane

In a worm gear this is a plane perpendicular to the gear axis and contains the common perpendicular of the gear and the worm axis.

chordal thickness

Length of the chord subtended by the circular thickness arc.

chordal addendum

The height from the top of the tooth to the chord subtending the circular-thickness arc.

circular pitch

Length of the arc of the pitch circle between the centers or other corresponding points of the adjacent teeth.

contact diameter

The smallest diameter on a gear tooth with which the mating gear makes contact.

contact stress

The maximum compressive stress within the contact area between mating gear tooth profiles.

1/3

The lowest permissible water level shall be at a point of the height of the shell.

normal circular pitch

Is the circular pitch in the normal plane.

circular thickness

Also known as tooth thickness or the length of the arc between the two sides of a gear tooth, on the pitch circles unless otherwise specified.

clearance

The amount by which the dedendum exceeds the addendum of the mating tooth.

central diameter

The smallest diameter on a gear tooth with which the mating gear makes.

contact ratio

The ratio of the arc of action to the circular pitch.

conjugate curve

Is the curve that satisfy the law of gearing.

cycloid

The curve formed by the path of a point on a circle as it rolls along a straight line.

dedendum

The depth of tooth space below the pitch circle or the radial dimension between the pitch circle and the bottom of the tooth space.

dedendum circle

Is also known as root circle or is the circle that bounds the bottoms of the teeth.

diametral pitch

The ratio of the number of teeth to the number of millimeters of pitch diameter.

normal diametral pitch

Is the diametral pitch calculated in the normal plane and is equal to the pitch divided by the cosine of helix angle.

effective face width

That portion of the face width that actually comes into contact with mating teeth, as occasionally one member of a pair of gears may have a greater face width than the other.

efficiency

The actual torque ratio of a gear set divided by its gear ratio.

epicycloid

When it rolls along the outer side of another circle.

external gear

A gear with teeth on the outer cylindrical surface.

face of tooth

That surface of the tooth which is between the pitch circle to the top of the tooth.

face width

The length of the teeth in axial plane.

face

Is the surface of the tooth between the pitch cylinder and the addendum cylinder.

fillet curve

The concave portion of the tooth profile where it joins the bottom of the tooth space. The approximate radius of this curve is called the fillet radius.

fillet stress

The maximum tensile stress in the gear tooth fillet.

flank of tooth

That surface which is between the pitch circle and the bottom land.

flank of tooth

Is the surface of the tooth between the pitch and root cylinders.

gear ratio

Is the number of teeth in the gear divided by the number of teeth in the pinion.

helix angle

The angle that a helical gear tooth makes with the gear axis.

helical overlap

The effective face width of a helical gear divided by the gear axial pitch.

hypocycloid

When it rolls along the inner side of another circle.

internal diameter

The diameter of a circle coinciding with the tops of the teeth on an internal gear.

internal gear

A gear with teeth on the inner cylindrical surface.

involute

The curve formed by the path of a point on a straight line, called the generatrix, as it rolls along a convex base curve.

top land

Is the top surface of the tooth.

bottom land

Is the surface of the gear between the fillets of adjacent teeth.

lead

The distance a helical gear or worm would thread along its axis in one revolution if it were free to move axially.

line of action

The path of contact in involute gears. It is a straight line passing through the pitch point and the tangent to the base circles.

length of action

The distance on an involute line of action through which the point of contact moves during the action of the tooth profile.

module

Is the ratio of pitch diameter in millimeter to the number of teeth, mm.

normal plane

A plane normal to the tooth surfaces at a point of contact, and perpendicular to the pitch plane.

outside diameter

The diameter of the outside circle.

pitch

The distance between similar, equally spaced tooth surfaces, in a given direction and along a given curve or line.

pitch angle

Is the angle subtended by the arc on the pitch circle equal in the length to the circular pitch.

pitch diameter

The diameter of the pitch circle.

pitch circle

A circle the radius of which is equal to the distance from the gear axis to the pitch point.

pitch point

For meshing gears, is the point of tangency of the pitch circle.

pitch plane

In a pair of gear it is the plane perpendicular to the axial plane and tangent to the pitch surfaces.

plane of rotation

Any plane perpendicular to a gear axis.

pressure angle

The angle between the tooth profile and a radial line at its pitch point in involute teeth, the angle between the line of action and the line tangent to the pitch circle.

principal reference plane

The pitch plane, axial plane, and traverse plane, all intersect at a point and are mutually perpendicular.

rack

A gear with teeth spaced along a straight line, and suitable for straight line motion.

roll angle

The angle subtended at the center of the base circle from teeth origin of an involute to the point of tangency of the generatrix from any point on the same involute.

root circle

A circle coinciding with or tangent to the bottoms of the tooth spaces.

tangent plane

A plane tangent to the surfaces at a point or line of contact.

tip relief

An arbitrary modification of a tooth profile whereby a small amount of material is removed near the lip of the gear tooth.

tooth thickness

The width of tooth measured along the pitch circle.

tooth space

The space between the teeth measured along the pitch circle.

total face width

The actual width dimensions of a gear blank.

working depth

Is the radial distance from the addendum circle to the working depth circle.