key fasteners Flashcards
functions of a key fastener
secures the shaft to other devices such as couplings, sheaves, and gears. meant to make sure that the drive shaft and the driven component are locked together and do not slip on eachother
square keys
most widely used.
rectangular
looks like a square key except that its width is greater. can be parallel or tapered
saddle
used when no keyseat of any kind. used in light duty applications. very flat
Gib head
tapered square key with a head. meant for when only one side of the assembly is accessible
Offset
typy of square key where one side has a different width than the other
Woodruff
shaped like a half moon. Used for light duty because it has strong gripping strength
what features do suppliers use to specify keys and key-seats
nominal width and height
width and height tolerance
length
material type
what is used to measure the width and depths of a key and keyseat
Dial or digital caliper
nominal width
the width of both the key stock and the key seat, without accounting for tolerance
nominal key height
height of the key stock, without accounting for tolerance. Not the same as key height. Is normally chosen to be half the key height because the key must extend into the keyseats of both the hub and shaft
width and height tolerance
allowable variations of the width and height dimensions of the key and keyseat
two types of fits as determined by the ANSI and their differences
class 1: looser fit than class 2. is a type of clearance fit called a sliding fit.
what does a sliding fit mean
there’s a slight difference between the key and keyseat. should not be detectable by touch
undersize key stock
fits the tolerance specification shown for a class 1 fit
oversize key fit
the lower tolerance is zero. typical oversize tolerance is +0.0002 in. to 0.000 inw
common key materials and why they are used
Cold rolled steel
zinc-plated cold rolled steel
high carbon steel
brass
Used because they are softer than the shaft material, so that they will shear first if overloaded
over/undersize tolerance
there is both and upper and lower tolerance. typical example is +0.0005 in. to -0.0005 in. works best when you want a tighter than normal fit
three measuring tools used to measure the key and keyshaft
dial caliper
micrometer
ruler
cup point set screw
have a dished out area on their tip
flat point
have a flat tip
dog point set screw
have a point that fits into the hole of the shaft
oval point set screw
best when set screw will contact the shaft at an angle
cone point set screw
used for permanent mounting of components on shafts
soft tipped set screws
have a different(softer) material on the point. provides adequate locking strength and prevents damage and scarring to soft shafts
best way to remove a hub from a shaft
use a bearing puller. another is to use a key punch and soft hammer to tap the key out
