Dowel is employed in numerous, diverse applications. It is used to form axles in toys, as detents on gymnastics grips, and as structural reinforcement in cabinet making. In some applications, dowel rod is cut into short lengths called dowel pins. Dowel pins are used to secure two objects together; a hole is bored in both objects and the dowel is inserted into the aligned holes.
The dowel rod used in woodworking applications is made by feeding lumber through a circular cutter. It is commonly cut into dowel pins, which are used to reinforce joints and support shelves and other components in cabinet making. Some woodworkers make their own dowel pins, while others purchase precut dowel pins that are typically available in assorted lengths and diameters. Various systems, such as Dowelmax, have been devised to aid in dowel joinery.
Dowel-based joinery typically employs fluted dowel pins. A fluted dowel pin has a series of parallel grooves cut along its length. The fluting provides channels through which excess glue—which is used to secure the dowel pin in its hole—can escape as the dowel is inserted, thereby relieving the hydraulic pressure that might otherwise split the timber when the mating pieces are clamped together.
Steel dowels are commonly used in masonry to pin stone components together. Holes are bored in the stone and the steel dowels inserted to secure the components.
Dowel pins are often used as precise locating devices in machinery. Steel dowel pins are machined to tight tolerances, as are the corresponding holes, which are typically machined through a process called "reaming."
A dowel pin may have a smaller diameter than its hole so that it freely slips in, or a larger diameter so that it must be pressed into its hole. For example a 6 mm diameter dowel is typically machined to within 0.005 mm tolerances. Its corresponding 6 mm hole can be made to allow the dowel to be slip-fitted (e.g., with a +0.01 mm dimensional call out) or press-fitted (e.g., with an -0.01 dimensional call out) into the hole.
If no dowels are used for alignment (e.g., components are mated by bolts only), there can be significant variation, or "play," in component alignment. Typical drilling and milling operations, as well as manufacturing practices for bolt threads, introduce at least 0.2 mm (0.008 inches) play for bolts up to 10 mm (3/8 inches). If dowels are used in addition to bolts, the play is reduced to approximately 0.01 mm (0.0004 inches).
When designing mechanical components, Engineers typically use dowel holes as reference points to control positioning variations and attain repeatable assembly quality, regardless of who assembles the components.
In vehicles, dowels are used when precise mating alignment is required, such as in differential gear casings, engines, and transmissions.