Pin Joints

Pin joints

Pin joints are among the detachable joints. There are dowel pins, fixing pins and shear pins.

Dowel pins need not transmit any forces, but only locate two workpieces relative to one another. They make assembly easier.

Retaining or fixing pins are used to transmit small amounts of force, in place of screws.

Shear pins protect easily damaged parts against overloading. They transmit the full driving force. It the force becomes excessive, however, the pin shears off and separates the two halves of the joint. Alter the fault has been eliminated, a new shear pin has to be fitted.

Types of pin

Grooved pins (Fare cheap and easy to fit. They have three rolled grooves along the surface. When hammered in, the ridges are partly forced back into the grooves to provide a firm seat in non- reamed holes. Grooved pins are used as locating and locking pins.

Split sleeves are split hollow cylinders of spring steel, with a diameter 0.2 to 0.5 mm greater than the drilled hole into which they are inserted. The hole need not be reamed, since the force

exerted by the compressed sleeve provides the desired pressure.

Straight pins are usually supplied with either tapered or spherical ends. Hardened straight pins are used as dowels. The hole for the pin must first be reamed.

Taper pins have a 1 :50 taper. They are therefore easier to insert than straight (cylindrical) pins. The hole is reamed with a taper reamer until the pin can be pressed in by hand with its head 3 to

4 mm above the rim of the hole. The pin is then driven in to its correct depth. A threaded journal or internal thread enables the pins to be pulled out of the joint again if there is no provision for driving them out from the opposite side.

10.3 Keys and splines

Keys and splines are used to connect shafts and hubs together. They prevent the hub from rotating on the shaft. They can also prevent the shaft from sliding axially.

Feather keys have a taper (inclination usually 1 ; 100). The taper generates the pressure which creates a firm joint between the parts to be connected. There are driven taper keys and sunk keys. In a driven joint, the key is forced in between the shaft and the hub. ln a sunk joint, the key is first inserted into the slotin the shaft, and the hub assembly is then driven on to the shaft over the

key. The flat key and the saddle key can only transmit fairly small forces. This kind of joint is seldom used in automobile engineering.

Plain keys have no taper. They create a pure driving joint only, with the force transmitted by the site faces of the key. The keys have an interference fit in the slot in the shaft.

Parallel keys usually have a close fit in the slot in the hub. The hub has to be prevented from sliting laterally. The sliding key permits the hub to slide laterally, for example then shift gears in a gearbox. The Woodruff key is mainly used at the ends of taper shafts. In the case of splined shafts, shaft

and keys are integral. This joint is used on highly stressed transmission components. The serrated joint is similar to the splined shaft.

Shear pins protect easily damaged parts against overloading. They transmit the full driving force. It the force becomes excessive, however, the pin shears off and separates the two halves of the joint. Alter

the fault has been eliminated, a new shear pin has to be fitted.

Types of pin

Grooved pins  are cheap and easy to fit. They have three rolled grooves along the surface. When hammered in, the ridges are partly forced back into the grooves to provide a firm seat in non reamed holes. Grooved pins are used as locating and locking pins. Split sleeves are split hollow cylinders of spring steel, with a diameter 0.2 to 0.5 mm greater than the drilled hole into which

they are inserted. The hole need not be reamed, since the force exerted by the compressed sleeve provides the desired pressure.

Straight pins are usually supplied with either tapered or spherical ends. Hardened straight pins are used as dowels. The hole for the pin must first be reamed.

Taper pins have a 1 :50 taper. They are therefore easier to insert than straight (cylindrical) pins. The hole is reamed with a taper reamer until the pin can be pressed in by hand with its head 3 to

4 mm above the rim of the hole. The pin is then driven in to its correct depth. A threaded journal or internal thread enables the pins to be pulled out of the joint again if there is no provision for driving them out from the opposite side.

10.3 Keys and splines

Keys and splines are used to connect shafts and hubs together. They prevent the hub from rotating on the shaft. They can also prevent the shaft from sliding axially.

Feather keys have a taper (inclination usually 1 ; 100). The taper generates the pressure which creates a firm joint between the parts to be connected. There are driven taper keys and sunk keys. In a driven joint, the key is forced in between the shaft and the hub. ln a sunk joint, the key is first inserted into the slot in the shaft, and the hub assembly is then driven on to the shaft over the key. The flat key and the saddle key can only transmit fairly small forces. This kind of joint is seldom used in automobile engineering.

Plain keys have no taper. They create a pure driving joint only, with the force transmitted by the site faces of the key. The keys have an interference fit in the slot in the shaft.

Parallel keys usually have a close fit in the slot in the hub. The hub has to be prevented from sliting laterally. The sliding key permits the hub to slide laterally, for example the shift gears in a gearbox. The Woodruff key is mainly used at the ends of taper shafts. In the case of splined shafts, shaft and keys are integral. This joint is used on highly stressed transmission components. The serrated joint (Figure 10.31) is similar to the splined shaft.

10.4 Interference-fit joints

The parts to be connected are manufactured oversize, so that pressure is built up at the joint when the parts are assembled. Interference-fit joints can transmit longitudinal and transverse forces. They are easy and cheap to produce. but can only be separated with difficulty. Depending on the method of making the interference-fit joint, we distinguish between the following types:

Longitudinal press tits. The two parts are pressed together in an axial direction when cold.

Transverse shrink fit. The outer part is heated uniformly and placed over the inner part. After cooling, a shrink lit is obtained,

Transverse press fit by expansion. The inner part is cooled down unllormly and then placed inside the outer part. Alter regaining normal temperature, an expansion joint is obtained.