Dowel
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A dowel is a pin, usually made of wood, plastic or metal, used to secure two objects together. A hole is bored in one or both of the objects and the dowel is inserted into the hole.
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[edit] Woodworking
Dowels are commonly used in woodworking to reinforce joints. Dowels are also often used to support shelves and other components in cabinet making. The dowels are commonly cut from a length of dowel, which is a timber product made by drawing solid timber through a circular cutter forming a rod of a specified diameter. Precut dowels are also available in various lengths and diameters. A fluted dowel has a series of grooves cut in its length. The purpose of the fluting is to allow glue to squeeze out as the dowel is inserted so that excess glue does not collect at the bottom of the hole causing the timber to split when mating pieces are clamped together.
[edit] Stone masonry
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.
[edit] Machinery
In the design and assembly of machines, dowels are typically used as precise locating devices. Steel dowels are machined to very tight tolerances, and the corresponding holes for these dowels are also machined to very tight tolerances. For example a 6 mm dowel is typically machined to within 0.005 mm tolerances. Corresponding holes for dowels can be made to allow the dowel to be slip-fitted into the hole - for example with a +0.01 mm dimensional call out on a 6 mm hole), or press-fitted - for example with an -0.01 dimensional call out on a 6 mm hole
Without the use of dowels, if a component is mated to another component through the use of bolts only and no dowels, there can be quite a bit of variation in the location of the two components with respect to each other. Typical drilling / milling operations, as well as typical manufacturing practices for bolt threads mean that a bolt in a hole has typically a bit of play, at least 0.2 mm/ 0.008" for bolts up to 10 mm / 3/8". If dowels are used in addition to the bolts, the variation will drop to about 0.01 mm/0.0004".
Engineers typically use the dowel holes as reference points when they design the components to ensure that at assembly time the variation in position is controlled and is repeatable regardless of who assembles the components.
In vehicles, dowels are found anywhere where precise mating is required, such as differential gear casing, engine, transmission, etc.
