Gears Flashcards
If speed is increased what happens to torque in a gear train?
Decreased
What are the speed ranges (ratios) in a single reduction gear box?
5:1 - 70:1
What are the speed ranges (ratios) in a double reduction helical and worm gear box?
20:1 - 280:1
What are the speed ranges (ratios) in a double reduction 2 worm gear box?
25:1 -4900:1
What are the speed ranges (ratios) in a triple reduction 3 worm gear box?
1000:1 - 180 000:1
How much efficiency is lost in every gear configuration?
2%
How does speed affect cooling of a gear box?
Less speed typically equates to less cooling
What direction(s) do helical or herringbone gears have their shafts?
Parallel
Single Helical gears require what bearings?
Tapered roller bearings
Do single helical gears create thrust (y/n)
Yes
What type of bearings do herringbone gears require?
Radial bearings
Do herringbone gears create thrust? (Y/n)
No
What bearings do double opposed helical gears require?
Radial bearings
Why do double opposed helical gears not create thrust?
They push against each other opposed to one direction
When fitting gears what order should you follow?
Largest first
Pinion last
When/what are bevel gears used for?
Right angle drives typically with helical gears
What are the ratios of bevel gears?
1:1 - 10:1
What is the ratio of a mitre gear box?
1:1
What direction are the shafts in a hypoid gear?
Cross
What are the ratios of a hypoid gear?
2:1-8:1
What bearing are to be used with bevel, mitre, and hypoid gears?
Tapered roller bearings
Do bevel gears create thrust? (Y/n)
Yes
Do mitre gears create thrust (y/n)
Yes
Do hypoid gears create thrust (y/n)
Yes
Where are shafts located in a planetary gear?
In line
What are the 4 uses for planetary gear boxes?
Reduction
Overdrive
Reversing
Direct
What are the ratios for planetary gears?
1.1:1 - 50 000:1
What are the 3 main members to a planetary gear?
Ring
Sun
Pinions
What are the 2 type of ways a reducer is joined to a power source?
Direct
In direct
What are the two types of direct attachments between a reducer and a power source?
Flexible
Flanged
What type of base does a flexible connection between a reducer and power source require?
Strong / rigid
What is an in direct way of connecting a reducer to a power source?
V belts
What are the two main types of mounting styles of a gear box?
Base mounted
Shaft mounted
What is important to remember when mounting a base mounted gear box?
The orientation in reference to the oil level/lubrication method
What is the purpose of a torque arm?
To hold a unit in position preventing rotation
Where should a torque arm be mounted?
Right angle from the output shaft to point of attachment
What is the two main benefit of using V belts to power a gear box?
-Extra variation in speed by using different sized sheaves
-overload protection
Where should V belts be mounted on a gear system?
Right angle to a line between output and input shaft
What are the 4 methods for lubrication of a reducer?
Splash
Wipers
Pump
Provisions
What lubrication method does worm gears typically have?
Wipers
What lubrication method does vertically mounted units typically have?
Provisions to the bearings
What does chordal mean?
Engagement
Where is the pitch point on a gear?
Where the teeth make contact
How do you find the ratio of a worm gear?
of teeth on the wheel : # of starts on the worm
What are the 3 typical pressure angles?
14.5 degrees
20 degrees
25 degrees
In pressure angles what is strongest?
The largest one (25)
What is the pressure angle on a gear?
The angle the teeth are cut at
What must gears that mesh have?
The same pressure angle
What are the 2 types of teeth profile on a gear?
Involute
Straight
What does an involute gear tooth look like?
Curved
Where is the pitch circle on a gear?
Middle of the teeth
Where is the root diameter on a gear?
Bottom of the tooth
If a gear train has clockwise (cw) drive gear at the start and an even number of gears what direction will the last gear rotate?
The opposite direction as the drive (counterclockwise ccw)
If a gear train has clockwise (cw) drive gear at the start and an ODD number of gears what direction will the last gear rotate?
Same as the first gear (clockwise)
If you have a gear train where the drive gear has 10 teeth and the driven gear has 30 teeth what is the ratio?
3:1
If a drive gear has 20 teeth and the driven gear has 30 what is being obtained?
Reduction of speed
Increase of torque
When calculating ratios in a gear train with only a 1 drive and driven do the middle gears matter?
No. Just the drive and driven
What is an open gear drive?
Heard exposed to the outside environment
What is a gear set?
Matched pair of gears manufactured together with the intent to mate together
What is classified as a gear train?
Two or more gears working together as a unit
When two gears that have a different number of teeth mesh together, what is the gear with fewer teeth called?
Pinion
In bevel and hypoid gear sets, the smaller gear is called a pinion but the larger gear can be called what?
Crown gear
Or
Ring gear
When the input speed of the gearbox is the same as the output speed what is it called?
Direct drive
A gear train with a SLOWER output speed than input speed is called what?
A reducer
A gear train with a faster output speed than input speed is called what?
Speed increaser
If a gear train has a large gear driving a small gear what is it called?
Speed increaser
If a gear train has a smaller gear driving a larger gear what is it called?
Speed reducer
What two things does a reducer do?
Reduce speed
Increase torque
What are the two purposes of overdrives?
Increase speed
Reduce torque
What can direct drives change?
Direction or angle
How can you tell the hand of a gearbox unit?
Seen from the input shaft view
(Looking at the input, the direction the output comes from tells you the hand)
What direction of rotation are MOST gearbox units, clockwise or counterclockwise?
Clockwise
What the minimum units of reduction in a reducer?
2 or more
How do you find your gear ratio on a spur gear?
Driven gear / driving gear
(Driven divided by driving)
OR
Output / input
What is a compound gear?
A number of gears fixed together
(NOTE: not fixed by teeth)
What is the difference between helical gears vs spurs gears?
Spur gear teeth are straight
Helical gear teeth are at an angle
What is backlash?
The clearance between the gear teeth
What is a gear that only has bearing support on one side called?
Overhung
Gears that are supported between two bearings are called what?
Straddle mounted gears
Are work gears typically self locking? (Y/n)
Yes
What is the difference between opposed double helical gears and herringbone gears?
Herringbone comes to a point
Double helical have a space or gap
What is the module in terms of gear teeth?
The thickness
The bigger the number the bigger the thickness
If two members of a planetary gear are locked what does it do?
It acts as a direct drive
Where do we ideally want a worm gear contact set up in terms of the worm wheel?
SLIGHTLY towards the leaving side of the worm wheel
What does the term throated mean in terms of gears?
Beveled to increase tooth contact
Why would we permanently stamp numbers into gears?
To accurately take future measurements
Timing to ensure gears are assembled the same
What does the term toe refer to in bevel and hypoid gears?
The smallest part of the gear tooth
What does heel refer to in terms of bevel and hypoid gears?
The largest part of the gear tooth
Describe residual magnetism
Gears and bearings become magnetized attracting small particles
What is the purpose of the oil scraper?
Direct oil where needed
What are gears for?
Transmit power and motion
Why would we select a double throated work gear drive for a power train reduction?
Smooth operation and deep reduction ratios
What must a pair of gears have to mesh?
Same pressure angle and diametrical pitch
What is backlash
Space between the teeth of meshing gears
What is a gear train that converts linear to rotary motion?
Rack and pinion
What worm and gear drive has the most critical bearing adjustment setup?
Double throated
What is an overhung gear?
Supported by bearings on one side only
In a gear train what are the gears having no effect on ratio called?
Idler gears
What are two common tooth pressure angles of spur gears?
14.5
20
Why would we select spur gear drive for a power train reduction?
Economical to purchase, operate and maintain
What is the space between the top land of one gear and the root of a meshing gear tooth called?
Clearance
What are backlash measurements used to keep track of?
Gear wear
What is used for checking for cracks in gear teeth?
Penetrant dye and developer
What are broken gear teeth a sign of?
Shock or over loading
What is tolerance stack up?
Slight variations in machining that add up to a sum total
Gears and power transmission devices are used where you want ___________________
Positive positioning and ratio
What gear is typically the smallest in a two gear train?
Pinion gear
A good mesh pattern between two mated gears is indicated by what?
A central pattern not contacting the tooth edge
What is the MA of a 160T worm wheel being rotated by a four start worm?
40:1
What is the bottom half of a gear tooth called?
Dedendum
What are the three methods for checking hearing backlash?
Dial
Lead wire
Feeler gauges
What is the purpose of an oil dam in a gearbox?
Gathers and directs oil over the gears and bearings
What components are in a planetary gear assembly?
Sun gear
Ring gear
Planet gears
Carrier
If gear (driver) has 10T, turning at 125rpm, meshes with gear B (driven), having 250T, what is the mechanical advantage (ratio) of this reduction gear box?
25:1
A double reduction helical gearbox gearbox has a 12/60 input gear set and a 16/80 output gear set. What is the gearbox’s reduction ratio?
25:1
Damaged hardened gear teeth may be hand worked to remove burrs and high points with what tool?
Abrasive file
What is the main reason for selecting the use of a hypoid gear?
Smooth and quiet operation
A gear train has 9 gears meshing together the input gear is rotating clockwise what direction is the 9th gear turning?
Clockwise
In a planetary gear set if the sun is held what will the carriers output be?
Same direction speed reduction
When removing an old gasket from a flange or gearbox what must you ensure?
Old pieces of gasket do not fall into the system
When removing old O rings during a rebuild what is the best practice to follow?
Always replace the O rings
What must a pair of gears have to mesh?
Same pressure angle and diametrical pitch
What worm and gear drive has the most critical bearing adjustment setup?
Double throated
In a planetary gear set if the sun is held what will the carriers output be?
Same direction speed reduction
A double reduction helical gearbox has a 12/60 input gear set and a 16/80 output gear set. What is the gearbox reduction ratio?
25:1
What do you shim to get the correct rotational torque on a hypoid input gear?
Pinion preload
