Dowels and Pins

Dowels and pins used in aircraft can include the Roll Pin, Clevis Pin, Split (Cotter) Pin and Taper Pin.

Dowels

While not usually used as fasteners, dowels are rods or pins of the appropriate material which are fixed (often permanently) in one of the components of a joint such that the protruding shank of the dowel locates with a corresponding hole in the item being attached, thus ensuring accurate assembly.

Two examples of the use of dowels may be found where a Propeller Control Unit is attached to an engine casing and there is a requirement for absolute accuracy in the alignment of the oil tubes and again, where the segments of an engine compressor need to be joined with precision so that the rotating members do not foul the stationary parts.

Roll Pins

Roll pins (refer to figure below) are often used to secure a pulley to a shaft or to provide a pivot for a joint where the pin is unlikely to be removed.

A roll pin is normally made from flat spring steel, which is rolled into an incomplete cylindrical shape that allows the pin to compress when it is pressed into the hole and creates a spring action that holds the pin tight within the bore of the hole. To remove a roll pin, it must be driven from the hole with a correct-sized punch.

FIGURE

Clevis Pins

Clevis or flat-head pins (refer to figure below) are used for hinge pins in some aircraft control systems. They are made of cadmium-plated steel and have grip lengths in 1/16 inch increments. When a clevis pin is installed, a plain washer is usually placed over the end of the shank and a cotter (split) pin is inserted through the pre-drilled hole in the clevis pin, to lock it in place.

FIGURE

Taper Pins

Both the plain and threaded taper pins (refer to figure below) have a taper of 1 in 48 and are used in various locations during aircraft construction. They are designed to carry shear loads and are manufactured from high-tensile steel. The pins do not allow any loose motion or play and are used for joining tubes and attaching collars to shafts.

The plain taper pin is forced into the hole, which is reamed to the specified size with a Taper Pin Reamer and is held in place by friction alone. To ensure security, it can also be wire locked in place by passing the lock wire through the pre-drilled hole in the pin then securing the wire around the shaft.

Plain taper pins, which have no lock wire holes may have their smaller ends peened, after being installed to secure them in their holes.

The threaded pin is similar to the plain pin except that its small end is threaded to accept either a self-locking shear nut or a shear castle nut with split pin.

Some taper pins can be found with a split small end, which can be spread much like a split pin to prevent it loosening. These pins are sometimes referred to as bifurcated taper pins. All taper pins are measured by the diameter of their small end and their overall length.

FIGURE