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Gear drives Millwright Mechanics lvl 2 Exams Prep
- Gears increase speed using an Overdrive unit
- Gears reduce speed and increase torque using a Reduction unit
- connect shafts by using a gear train Gears
- What is the pitch circle of a gear? Circumference of the cylinder
- What is the pitch line? Line of contact between 2 cylinders
- What is the addendum? 1) amount of gear tooth
- the amount of the gear tooth above the pitch circle above pitch circle
- the amount of the gear tooth below the pitch circle
- On a gear chart, where is the addendum located? Between pitch circle and outside diameter
- On a gear chart, where is the circular pitch (CP) locat- ed?
The distance between two corresponding points on adjacent teeth, measured on the pitch circle
Gear drives Millwright Mechanics lvl 2 Exams Prep
- On a gear chart, where is the Dedendum located? Between pitch circle and root diameter
- On a gear chart, where is the clearance (CL) located? It's the gap between working depth and the whole depth
- What is the diametral pitch and what is the formula? Total number of teeth on the gear divided by pitch diameter in inches DP = N / PD
- What is the pitch diameter? Diameter of pitch circle
- Diametral pitch, pressure angle, and tooth profile are integral to proper of gears
Meshing
- What is the whole depth? Total height of a tooth OR the total depth of a tooth space
Gear drives Millwright Mechanics lvl 2 Exams Prep
- Why are spur gears with 20 degree angles preferred over gears with 14.5 degree angles?
- How can you visually identify a spur gear with a 20 degree pressure angle?
- How can you visually distinguish a 14.5 degree pres- sure angle spur gear?
Greater strength and wear resistance
Bottom tooth width is larger than the top
When 2 tooth widths look about equal
- Involute profile means of the tooth Shape
- What happens when 2 meshing gears with the same DP (diametral pitch) and pressure angle but different number of teeth are used together?
- utter destruction
- tooth wear increases
- enhances rolling action of teeth
- none of the above
Enhances the rolling ac- tion of the meshing teeth
- What is the formula for backlash? 0.030/DP
- What is backlash? Amount of play between mating teeth
- What are 3 purposes of backlash? 1) allow for heat expan- sion
- prevents interference with incoming and outgo- ing teeth
- Lubrication escape route
- Backlash
Gear drives Millwright Mechanics lvl 2 Exams Prep
Lack of in gears prevents lubricants from escaping and causes extreme noise and wear
- Backlash is measured in...? Thousandths of an inch
- When lubricants cannot escape from meshing teeth, what kind of pressure is created?
- Gears are primarily made from these 3 material groups:
- What advantage do steel gears have over other fer- rous types?
- What advantages do cast iron gears have over other ferrous types?
Hydraulic. Forces gears apart. No good can come from this
Ferrous metals Non ferrous metals Non metallic materials
When heat treated, they carry the greatest loads and torque
Easy to machine Cheap Wear resistance Run quietly
- What is a disadvantage of cast iron gears? Brittle
- Stainless steel gears are used in situations where resistance is vital
- What are the 2 most common non ferrous metals for gears?
- gears are tough and wear resistant, easy to cast and machine
Corrosion
Bronze and aluminum
Bronze
Gear drives Millwright Mechanics lvl 2 Exams Prep
- What is the main function of rack and pinion gearing? Converts rotary motion to linear motion and vice ver- sa
- What is the standard angle of a helical gear? (Aka the helix angle)
- A pair mating helical gears must be of:
- same direction of tooth slope
- different diametral pitch
- opposite direction of tooth slope
- different pressure angle
45 degrees
- opposite direction of tooth slope (opposite hand)
- When parallel shafts are connected by one set of heli- Axial thrust cal gears, what type of force is generated?
- How is axial thrust compensated for on helical gears connecting parallel shafts?
- To connect crossing shafts, which set up would you use?
- pair of mating gears of the opposite hand
- 2 gears with the same hand of rotation.
- angular bevel gears
- bevel gears
Axial thrust bearings
- 2 gears with the same hand of rotation
- Which gear set up is used to connect shafts that inter- 1) bevel gears sect and usually at right angles?
- bevel gears
- helical gears with opposite hand rotation
- helical gears with same hand of rotation
- angular bevel gears
Gear drives Millwright Mechanics lvl 2 Exams Prep
- In bevel gears, the smaller one is called the and Pinion and ring
the large gear is called the
- Why are bevel gears sold as a matched set? Pitch-cone angles of the meshing gears are related to the shaft angle
- In bevel gears, if one has a pitch-cone angle of 90 degrees it's called a
Crown
- What is the shape of a crown gear? Disk shape
- In bevel gears, if the pitch-cone is greater than 90 degrees, what is the gear called?
Internal bevel
- What is the shape of an internal bevel gear? Cup shape
- Which gears have curved teeth at a zero angle? Zerol (trademark name)
- Which runs the loudest: zerol, straight bevel, or spiral Straight bevel bevel
- gears have several teeth meshed at one time and develop axial thrust
- gears connect shafts that intersect at other than 90 degrees
- gears change shaft direction and generate a 1:1 ratio?
- gears transmit power between shafts that cross but do not intersect
Spiral bevel
Angular bevel
Mitre
Hypoid
- Hyoid and spiral bevel
- Non-throated, single throated, and double throated are the on worm gear sets
- What are the three contact patterns on worm gear sets?
- In this worm gear contact type, the outline of the worm gear teeth curves to match the shape of the worm
- non throated
- single throated
- double throated
- In this worm gear contact type, the worm profile is modified to increase contact between worm and worm gear curve
- non throated
- single throated
- double throated
Contact patterns
Non throated Single Throated Double throated
Single throated
Double throated
- In this worm gear contact type, teeth on the worm all 1) non throated have the same depth and linear pitch
- non throated
- single throated
- double throated
- Which of the 3 worm gear contact types has only 1-2 tooth engagement that leads to early wear and failures?
Non throated
- Worm and worm gears create what type of thrust? End
- units increase speed which results in torque loss
- units consist of a pair of gears in a rigid, strong, movable housing
Overdrive
Reduction
- What is the purpose of a reduction unit? Reduce speed and in- crease torque
- A single reduction unit has gears and shafts
- 2 and 2
- 4 and 3
- 2 and 3
- 4 and 4
- A multiple reduction unit has or more gears on or more shafts
- 3 and 4
- 4 and 6
- 6 and 4
- 4 and 3
- In worm gear reduction units, bearings are needed to allow for loading of gear action
2 and 2
4 and 3
Axial thrust and thrust
- What should you do before removing any type of bear- Make damn sure you got ings?
- When fitting worm gear reduction units, are needed to get the correct bearing
some replacements avail- able Because, holy shit, that won't be a good time.
Shim packs and preload
- Rule of thumb: which order should gears be fitted in reduction units?
1) pinion, intermediate gears, largest 2) intermediate gears, largest, pinion 3) largest, intermediate, pinion 4) any order is fine
- How is correct backlash established in herringbone gears?
- largest, intermediate, pinion. =g‹et it?
By centre to centre dis- tance of shafts
- Herringbone gears cannot have the adjusted Backlash
- Bevel, mitre, and hypoid gears develop Axial thrust
- bearings are used where axial thrust is pre- sent
Tapered roller
- Planetary gear sets have which 3 drive members? Sun gear Ring gear Carrier aka YOKE ( holds pinion(s) )
- In planetary gear sets, which drive member(s) can be either the input or output?
1) sun 2) ring 3) carrier (aka yoke) 4) any of them
- For direct drives; a reducer and power source can be joined in two ways: name 'em
Any of them!
With a flexible coupling, both units need to be Bolted to a strong base ( same base )
- Shaft mounted reduction units have a output shaft
A flange mounting, used with combo units
Hollow
- Shaft mounted reduction units have a torque arm that Right angle should be as close to a as possible
- On shaft mounted reduction units, the drive is at right angles between the output and input shafts
V belt
- An indirect drive for reducer and power source can be V belts
joined in which 2 ways
- What lubrication method is most common in reduc- tion units?
Chain drives
Splash
- For indirect drives where a reducer and power source Separate are joined, the units can be on bases
- *mitre gears are bevel gears that have the
number of teeth and pitch
Same
