Keys, keyseats and setscrews Flashcards by Brandon Hatt

Transmits motion and power from one machine to another using gears, belt pulleys and sheaves, or chain sprockets.

A shaft

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In relation to a shaft, hub and key, this is crucial to smooth running and long life

The fit

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Locates parts precisely and provides a positive means to transmit torque

A key

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When is more than one key required?

When the shaft is transmitting a large amount of torque

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A _____ is an axial (longitudinal) groove accurately cut into the shaft or hub to retain a key

Keyseat

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Loose fitting keys are a:

Hazard and can cause system failure

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The most important concerns when selecting a key are? (8)

Shaft size, 
hub diameter, 
style of mounting, 
torque, 
material, 
permanent or semi permanent, 
intended use, 
engineering specs.

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_____ keys, top and bottom are parallel and sides are parallel. Keystock is readily available, usually hand fit and slightly oversize. Low to medium carbon steel.

Parallel keys

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When making a parallel key, this material can be used, however it is made to a minus tolerance.

(Sizes up to 0.75”, -0.002”)
(Sizes 0.75” - 1.5”, -0.003”)

Square bar stock

Such as AISI 1018

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The most common types of parallel keys have _____ or _____ cross sections

Square or rectangular

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Rectangular keys are sometimes referred to as _____

Flat keys

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Square and rectangular keys can be used with _________ shaft sizes

All

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Square keys are often recommended up to a shaft diameter of 165mm (6.5”). Above that, _____ is recommended

Rectangular aka “flat” keys

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_____ key is used when a shaft keyseat is a different width than the mating hub keyseat. This key may also be used to align parts.

Stepped aka offset key

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_____ key is shaped to fit the curvature of the shaft. No keyseat is required for the shaft, only the hub.

Normally has several set screws and depends on friction between shaft and key to provide drive as the shaft rotates.

Only suitable for light drive fits.

Saddle key

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Square or rectangular key that has its ends rounded. Both the burried key and Pratt and Whitney key are examples of this.

Length is equal to the keyseat, and less than hub width.

Boxed (blind) keys

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Similar in shape to square boxed keys, they are set deeper into the shaft and used where mating machine components restrict accessibility at both ends of they key.

Sunk key

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This key permits end movement of the two parts either in operation or assembly, and comes in two types: fixed and sliding.

Feather key

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What are the two types of feather keys?

Fixed and sliding

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This type of feather key has a tight fit in the shafts keyseat. Sometimes secured by screws, allows the hub a certain amount of axial sliding motion while preventing rotation.

Fixed feather

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____ keys can also serve as a fixed feather key

Sunk key

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This type of feather key is secured in the outer hub and slides along a keyway in the shaft. Secured by shoulders on either end of the hub, or a pin fit into a hole drilled through the hub into the center of the keyseat.

Sliding feather

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A square or rectangular key with an enlarged head on one end is called a:

Allows for easier extraction where parts are removed at frequent intervals.

Gib-headed key

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For safety, restrict the use of gib headed keys protruding from shafts. This is because:

Avoids any material tangling during rotation.

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____ key does not require a set screw. When driven in tight, it secures the component securely to the shaft. Can be made with a gib head to assist in removal.

Tapered key

Semi-circular key used in light duty applications, such as small electric motors, hand wheels, or small gears with tapered shafts.

Woodruff key

The last two digits of a Woodruff key's code give you the nominal diameter in:

Eighths of an inch #406 = 06 * 1/8" = 3/4"

The first digit of a Woodruff key's code gives you the width of the key in:

Thirty-secondths of an inch #406 = 4 * 1/32 = 1/8

As a rule of thumb, with Woodruff keys, the diameter is the same as:

The shaft diameter

As a rule of thumb, with Woodruff keys, the width of the key is:

One quarter the nominal diameter of the shaft

When a Woodruff key is not available, one can be made from:

Round bar stock with the required diameter

All keyseats cut into the outside of shafts or cylinders have their sides in line with the ____ of the shaft

Axis

Woodruff keys have a _____ at the base

Radius

Parallel keys have their bases ______ and _____ to the shafts axis

Flat and parallel

A parallel keyseat cut at the end of a shaft is called a:

Open keyseat

A parallel keyseat cut anywhere along the shaft is called a:

Boxed keyseat

When cutting a keyseat, an end mill will produce a _______ keyseat

Profile

When cutting a keyseat, horizontal milling cutters produce a:

Sled runner or run out keyseat

This keyseat is used when the exact position of the mating part is not known, or the position may vary slightly. Also used when the key is installed after the hub, or when the key is removed before the hub.

Open keyseat

The keyseat in both the shaft and hub are designed so exactly ___________ the height of the key is bearing on the side of the shaft keyseat, and _________ the height of the key is bearing on the hub keyseat.

Half and half

This keyseat may me located anywhere on the shaft, and is used when the location of the mating part is known. The length of the keyseat is generally shorter than the hub width.

Boxed keyseat

What is the maximum angular misalignment when cutting a keyseat in a shaft?

0.10 mm (0.002") over 100mm (4")

What is the maximum offset misalignment when cutting a keyway in a shaft?

0.25 mm (0.010")

The proper depth of the keyseat is measured:

Diametrically, from bottom of the keyseat to the opposite side of the shaft.

A Woodruff keyseat is a:

Circular recess cut into a shaft

For Woodruff keys up to _____" in diameter, shank style keyseat cutters are available. Larger cutters are mounted on arbors.

1.5"

Keyseats cut into the bores of attachments may either be _____ or _____

Parallel or tapered

Keyseat location in the hub of the attachment is critical when:

Strength or timing is important

Parallel keyseats cut into the bore of an attachment are cut deep enough to accommodate:

Half the height of the key plus clearance

As a rule of thumb, how do you determine the width of key to use?

One quarter of the diameter of the shaft.

What would you use to cut a keyseat in a shaft, without dismantling the machine components?

A portable keyseat cutter

End mills used to cut keyseats in a shaft are called _____. They can plunge cut to produce a boxed keyseat

Slot cutters. They have a tolerance of +0.0000 and -0.0015 on the diameter.

It is recommended that a shaft keyseat be first cut with:

The next smallest size end mill

What tool is used to cut a keyseat in the bore of an attachment?

Broach

The cutting action of a broach us performed by a series of teeth, each protruding about _____ further than the preceding tooth. The last 3 are the same depth, to provide the finishing cut.

0.07mm (0.003")

Each pass of a broach cuts to ____.

1/16"

____ broaches do not require shims as the standard depth is achieved in one pass

1/8" broach or any "one pass broach"

When using a broach, always lubricate:

The back of the broach, and use cutting fluid on the teeth

When using a broach, stop and check alignment:

During each pass

When using a broach, ensure ____ teeth are engaged at all times

What three things can reduce or prevent "hogging in" with a broach on softer metals?

Reducing back clearance on broach teeth, Reducing pressure or spring on the broach just before the finishing teeth pass, Use a collared bushing above the work to give support

What can help with the assembly of the shaft/hub/key?

Anti seize product or oil, small chamfer on front end of the key.

Tapered keys are fit into their components ______ assembly

After

Where several components are assembled on the same shaft:

Match mark every key, hub, and keyseat position

This class of fit is a relatively free fit for the key to slide into the keyseat. Standard square steel bar stock produces this fit.

Class 1 fit

This class of fit is a relatively tight fit. Hub should have a tight slide fit on the key. Keystock produces this fit.

Class 2

This class of fit is for permanent assemblies. No relative movement between shaft and hub.

Class 3

What does heavy chamfering of a key affect?

Reduces area of the sides, and increases load per unit of area on the key.

Always coat a key with _____ or ______ before driving it into the keyseat

Oil or anti-seize

What are the advantages of using an adhesive over a setscrew for securing a key? (3)

Does not require costly operations of drilling and tapping Bond is distributed evenly over joining area Holes for screws are eliminated, full strength of part is maintained

What are the disadvantages of using adhesives over a setscrew in securing a key? (2)

Surfaces must be prepped Heat can reduce strength (should not be used over 93°c)

What are the four styles of set screw head?

Hexagon socket, slotted socket, flat socket and square.

Why is the square style of set screw head at a disadvantage compared to other styles?

The protruding square head can catch loose materials

This type of set screw cuts into the metal as it's tightened. This gives axial and torsional holding power without increasing installation torque values. Can leave a burr in materials and cause parts to bind up on disassembly.

Cup-point

In regards to set screws, when vibration is a concern, or permanent positioning is desired, what style set screw point is selected?

Knurled cup point set screws

This type of set screw point is used to secure components to hardened shafts and keyed assemblies, without damaging the shaft via the set screw point.

Flat point set screw

This type of set screw point is used for the same applications as cup point, but require the shaft be scribed and spot drilled where the point meets the shaft.

Cone point

This set screw point style is used to lock parts that are adjusted frequently. It generally requires a groove of the same contour as the tip be provided on the shaft.

Oval point set screw

This set screw point type engages directly in slots milled longitudinally in shafts. The point also acts as a stop to limit travel. Allow for lengthwise movement but prevent rotation.

Half dog point

Similar to half dog point, but aren't any more efficient and therefore are seldom used and specially ordered

Full dog point

Set screws, unlike most other screws, are _____ fasteners

Compression fasteners

What variables can affect set screw holding power? (7)

Point type, thread finish, thread lubrication, diameter, size, location, number of set screws

When a set screw is tightened, a ____ is developed against the shaft. The magnitude of the _____ determines how well it will hold.

Thrust

_____ of the threads of a setscrew helps to ensure maximum thrust is exerted for maximum holding power.

Lubrication

Square and rectangular keys are often held in position with a _____ in the component over the key.

Set screw

Some applications require more than one set screw to secure a keyed hub to a shaft. In this instance, place the set screws at ___° to each other

90°

_______ screws have the same diametral dimensions as set screws, but are much shorter. The hexagonal driving socket is broached clear through the screw. For most sizes, the length is 1/2 diameter.

Socket locking screws

Always replace a set screw when:

The equipment has a major overhaul, There's any sign of wear to the head or threads, If it's a stainless steel set screw, replace it every time it is serviced.

Why should a stainless steel set screw be replaced whenever serviced?

Work hardening can cause the head to fail and reduce thrust exerted, reducing holding power. Removal is also impaired.

What tool is used to remove a gib head key?

Fox wedge. May need to be lubricated, may need a second one for a straight pull.

If the tapered key cannot be driven out:

The hub can be pushed out along the shaft to release the keys grip.

What methods can be used to remove a parallel key at the end of a shaft?

Drill/tap for a slide hammer, Weld a rod or use locking pliers for better grip, Key drift in keyseats that are milled long enough.

What tool is sometimes needed in combination with a key drift?

Spacer aka dutchman