Keys And Keyseats Flashcards
Why is the fit of shafts and their attachments imported to the machine?
The fit is crucial to smooth running and long life of the machine
Poor fit = poor life
What are Keys and keyseats (keyways) used for? (2)
To locate parts precisely
To positively join parts together
A __________ is an axial (longitudinal) groove accurately cut (machined) into the shaft or hub to retain a key
Keyseat (keyway)
What dictates the key choice?
-shaft size
-hub diameter
-mounting style
- torque exerted
-type of material
-intended use
-life of installation (permanent or semi)
-engineering specs
What is typical key stock material?
Low to medium carbon steel
Ex: 1020
What does AISI stand for?
American iron and steel institute
What is the difference of using cold finished square bar stock such as 1018 vs typical key stock 1020?
Square bar stock is made to a minus tolerance
Describe parallel keys
The top and bottom are parallel
The sides are parallel
What is the significance to key stock tolerances
Manufactured to a plus tolerance
What is the most common form of parallel keys?
Square or flat (rectangular) keys
What shafts can square and rectangular keys be used on?
All sized shafts
When would you use square keys instead of rectangular keys?
When the shaft diameter is up to or under 165mm (6 1/2 inches)
If a shaft diameter is 190.5mm (7.5 inches) would you use square or rectangular keys?
Rectangular
If your shaft keyseat is a different width than your hub keyseat what key would you use?
Step key (offset key)
Describe a saddle key
Shaped to fit the curve of the shaft but fitted to sit in the keyseat of the hub
If a key is square or rectangular that has both sides rounded what is it called?
Boxed or blind key
What key is this?
Box or blinded key
What key is shown in the picture?
Stepped or offset key
When is a sunk key used?
Where the mating machine components restrict access to the key on both sides
What is the significance to a feather key?
Permits movement of two parts either in operation or during assembly
What are the two types of feather keys?
Fixed feather key
Sliding feather key
Describe a gib headed key
A key with an enlarged head on one end
What is the purpose of a gib headed key?
Allows for quick extraction for parts that are removed frequently
What type of key is this?
Gib headed key
What is the standard taper for tapered keys?
1 in 96
1/8” in 12”
Metric is 1 in 100
What is a woodruff key?
A semi circular key but is also available with a flattened bottom
At what size are woodruff keys available with a flattened bottom?
1 1/2 inch
With woodruff keys which way does the semi circular sit?
Towards the shaft
What are the two ways a parallel keyseat may be cut?
Open
Boxed
If a keyseat is at the end of the shaft is is considered ____________
Open
If a keyseat is anywhere along the shaft it is considered to be _____________
Boxed
How is the shape of the end of the keyseat determined?
By the type of milling cutter used to cut the groove
A horizontal milling cutter produce what type of keyseat end?
Runout or sled runner
What type of keyseat end does an end mill produce?
Profile keyseat (straight)
What is the maximum tolerance for cutting an offset alignment keyseat?
0.25mm (0.010”)
What is the maximum tolerance for cutting an angular misalignment keyseat in a distance of 100mm (4”)
0.10mm (0.002”)
Is a set screw required to secure a woodruff key?
No
When is the location of the keyseat critical?
When strength or timing of the attachment is important
How deep are parallel keyseats cut in the bore?
Deep enough to accommodate 1/2 the height of the key plus clearance
When is a tapered keyseat used?
When using a tapered key
When should a tapered keyseat be longer than the key?
When the keyseat is NOT located at the end of the shaft
Who sets the standards for keys and their keyseats in relation to nominal shaft diameter?
ANSI
(American National Steel Institute)
What portable device is used to cut keyseats in the field?
Portable keyseat cutter
When picking your end mill to produce a keyseat to the correct dimensions you should __________________________
Cut first with the next smallest size end mill
How much material should you leave in a keyseat for finishing?
0.25mm (0.010”)
What is the size difference between teeth of a broach?
0.07mm (0.003”)
Each pass of a broach cuts to a depth of _________
1/16”
How do you adjust the depth of a cut with a broach?
By using shims
The degree of interference or clearance that a key has in relation to that shaft and hub is recognized as what?
The class of fit
How many classes of fit are there in terms of clearance of interference of a key?
3
What is the characteristics of a class 1 fit key?
Clearance fit
Relatively free fitting
How do you obtain a class 1 key fit with a parallel key?
Standard square bar stock and key seat tolerance
How do you obtain a class 2 key fit with a parallel key?
Key stock and Standard keyseat tolerances
What is a class 2 key seat fit described as?
Relatively tight fit with slight interference
How do you obtain a class 3 key fit with a parallel key?
Key stock and precision cut keyseats
How would you describe a class 3 key fit?
Interference fit (no relative movement)
What are the two main methods to secure a key to the keyseat?
Adhesive
Set screws
When should adhesives NOT be used to adhere a key to a keyseat?
When temperatures are above 93 Celsius
What are the 6 types of set screw points?
Cup
Flat
Cone
Oval
Half dog
Full dog
What is the benefit of using a cup point set screw?
Sharp edges dig into the metal of the shaft giving a very effective locking action
Where should a cup point set screw be used?
Where vibration is a concern and shaft marring isn’t an issue
What is the disadvantage of using a cup point set screw
It marks up the shaft
When are flat point set screws used?
When the shafts needs to remain not damaged at the screw point
What is the benefit of using a cone point set screw?
Similar to the cup but more precise
When are oval point set screws used?
When the part needs to be adjusted frequently
What is unique about the half dog point set screw?
Allows lengthwise movement but prevents rotational movement
How does the half dog set screw work?
Engages directly in slots milled longitudinally in a shaft to allow specific movement
What can help ensure the maximum thrust is exerted on the shaft from a set screw?
Lubrication
If you are adding more than one set screw where should you place them?
90 degrees to each other
How can a set screw be locked in place?
Using a socket locking screw
When should set screws be replaced? (3)
Major overhauls
Signs of wear
Every time if stainless steel
How do you remove a gib headed key?
Fox wedge(s)
What are the 4 methods to removing a parallel key?
Slide hammer
Vice grips
Key drift
Welding a rod to pull it out
What is the rule of thumb for finding the width of a key?
1/4 the diameter of the shaft
What is the rule of thumb for finding the diameter of a key?
Equal to the shaft diameter
What is the rule of thumb for finding the woodruff key sizes?
WD40
What is the size of a #406 woodruff key?
WD 40
4/32
06/8
Where are woodruff keys typically used?
Tapered shafts
Light duty work
How much of the height of a sunk key is in the keyseat (shaft)
2/3 of the key
How much of the height of a sunk key is in the keyway (bore)
1/3
When cutting your tapered keyseat where is it cut?
On the hub side
Where is the keyseat cut at an angle for tapered keys?
Hub
What type of setscrew has the best grip and tends to stay tight?
Cup point
Why do we chamfer all edges of parallel keys?
To clear the radius of the keyseat corners
What is the taper on an inch dimension tapered key?
1/8” per foot
Where are square keys used?
Most applications on shafts under 6.5”
What thickness key would you use on a 2” shaft under heavy load?
1/2”
When should a fixed feather key be used?
When you need to lock rotation but move axially
What type of keyseat can you cut with an end mill?
Profile key
What are splines?
External grooves and lands that manufacturers machine on a shaft to match with internal grooves and lands in a gear, collar, sleeve, or coupling
Where should you NOT use tapered gib head keys?
With cast iron hubs
What do taper pins require?
Tapered reamer
When are pin hubs normally drilled?
On assembly
What part of a dimension is the total permissible variation in its size?
Tolerance
To reduce stress turned down sections of a shaft should have what 2 things?
No more than 1.5:1 ratio
Large as possible fillet
What causes fatigue failure?
Repeated stress has work hardened it
Where would you measure axial runout?
The face of the attachment or hub
What is a class 1 key fitting?
Clearance fit
What is a class 2 key fitting
Tight fit
What is a class 3 fit?
Interference
What is a positive allowance?
Clearance fit
What is a negative allowance?
Interference fit
Where are rectangular keys used?
Large, hollow shafts, or thin diameter hubs
What would you do if a broach did NOT cut a keyway to full depth?
Use a shim under the broach
What sort of keyseat is cut with a horizontal mill and a side milling cutter?
Sled runner keyseat
