Gear drives
What is the purpose of backlash?
-Allows for tooth expansion due to heat -prevent interference with incoming and outgoing teeth -allow lubrication to escape
What are the three main groups of gear materials
-Ferrous metals -non ferrous metals -non-metallic materials
In respect to spiral bevel gears or helical gears... when the drive gear has a left hand spiral and is rotating counterclockwise, it's thrust is _______ the apex.
Away from the apex. Any endplay would increase the amount of backlash and create a less harmful situation (opposed to a right hand rotating clockwise)
Define backlash
Backlash is the amount of play between mating teeth. It is the difference between tooth space, and tooth width measured in thousands of an inche
Hypoid gear shafts cross, or intersect?
Cross
How do you determine the great ratio of a worm and worm gear/wheel set?
Divide the number of teeth on the gear by the number of starts on the worm.
What is the difference between a double helical gear and herringbone gear?
Double helical has a groove cut down the center. (To machine a true herringbone gear is expensive, and typically only done when very heavy loads are to be applied and space is minimal)
Spiral bevel gears run louder than straight bevel gears. True or false?
False
In internal spur gears, the connected shafts rotate opposite directions. True or false?
False. They rotate in the same direction
There are numerous output possibilities for a simple planetary gear set. Under proper operating conditions, one planetary gear set can provide: (5 possibilities)
Forward reduction Overdrive Reverse Neutral Direct drive
Most gear teeth have an ______________ profile.
Involute
To achieve maximum power capacity and life of the gears, the worm wheel should be set up so that the contact between the teeth is slightly toward the ________ side of the worm wheel.
Leaving side
What factors should be considered when choosing a gear material?
Load Speed Method of lubrication Tooth form Noise levels Environment Temperature
Which type of gear connects 2 intersecting shafts with an equal number of teeth on each gear?
Mitre gears. ("Equal number of teeth" = same Diameters therefore its a mitre gear) 1:1 ratio
Worm gearing sets can have three different contact patterns. They are referred to as?
Non throated Throated Double throated
Single helical gears connecting parallel shafts must be of the same hand, or opposite hand?
Opposite
The hand of drive of a reduction unit refers to the position of the _______ shaft as viewed from the _______ shaft
Position of the output shaft as viewed from the input shaft
What gear(s) concert rotary motion into linear motion, and video-versa?
Rack and pinion
Gears are used to connect shafts in various arrangements. List the main 4
Shafts parallel Center lines intersecting at 90 Center lines crossing at 90 Special cases when crossing or intersecting is not at 90
Circular pitch (CP)
The center to center distance between two teeth that are side by side, measured on the pitch circle. CP equals 3.1416 divided by the Diametral Pitch
Working depth (WKD) 2
The depth of a tooth engagement of two meshing gear teeth Working Depth equals 2 multiplied by the Addendum
Outside diameter (OD)
The diameter of the cylinder into which the gears are cut. OD equals (number of teeth plus two) divided by the Diametral Pitch
Pitch diameter (PD) or Pitch circle diameter (PCD) or or simply Pitch circle.
The diameter of the pitch circle PD = Number of teeth divided by the Diametral Pitch
Clearance (CL) .157
The gap between the working depth and the whole depth. CL = Dedendum minus the Addendum or .157 divided by the Diametral Pitch
The distance that one thread on a worm advances in one revolution is know as what?
The lead
Addendum (ADD) 1
The part of a tooth that lies between the pitch circle and the outside diameter of a gear. (Outer half of tooth) Addendum = 1 divided by the Diametral Pitch
Dedendum (DED) 1.157
The part of a tooth that lies between the pitch circle and the root diameter of a gear (inner half of a tooth including clearance) Dedendum = 1.157 divided by the Diametral Pitch
Chordal thickness (T) (Or tooth thickness)
The thickness of the tooth (at the pitch circle) on the face of the gear T = 1.57/DP
Chordal thickness (T)
The thickness of the tooth at the pitch circle on the face of the gear T equals 1.57 divided by the Diametral Pitch
Whole depth (WHD) 2.157
The total height of a tooth or the total depth of a tooth space. Whole Depth equals the Addendum plus the Dedendum (1+1.157=2.157)
Pressure Angle (and line of action)
Usually 14.5 or 20 degrees. The angle that the side of the tooth makes with a line drawn square to the pitch line is the "pressures angle". A line square to the pressure angle at the pitch line is the "line of action".
A positive infinitely variable drive is a type of overdrive. It is similar to what?
Variable speed belt drive
The direction of thrust generated by a single set of helical gears depends on what 3 things?
Wheather it is a drive, or driven shaft The direction of rotation The hand of the gear on the drive shaft
What are Zerol bevel gears?
Zerol bevel gears have curved teeth at a zero angle. This makes them run more quietly and smoothly then straight bevel gears. They are a intermediate type between straight bevel gears and spiral bevel gears.
Most spur gears have a pressure angle of _____ or _____. Which is preferred and why?
14.5 or 20. 20 degree pressure angle is preferred because of their greater strength and wear resistance and because they permit the use of fewer teeth on pinions.
What is the working depth of a gear tooth equal to?
2 Addendums
In a pair of helical gears, how many teeth mesh at the same time
2 or more, depending on the helix angle. This action creates a smooth, quieter drive.
The helix angle on a helical gear can range from a few degrees to the standard ___ degrees
45
DIAMETRAL PITCH (DP)
A constant number that dictates ALL dimensions of the gear tooth. The total number of teeth on a gear divided by the pitch diameter in inches. Diametral Pitch = Number of teeth divided by the Pitch Diameter
