The manufacturing costs are going to be inversely proportional to mechanical tolerances so you must balance you need for mechanical precision against the cost of the materials and other factors such as how easy it is to serviced and if it can be manufactured. Bolts up to 10 mm (0.394 in) in diameter typically have play on the order of 0.2 mm (0.008 inches). For example, when dowels are used in addition to bolts, the tighter dimensional tolerances of dowels and their mating holes-typically 0.01 mm (0.0004 inches)-result in significantly less play, on the order of 0.02 mm (0.0008 inches). When it comes to drilling, operations might introduce mechanical play with its fasteners. This variation can be avoided with proper use and installation of dowel pins in the design of any component. If the dowels were not used for alignment, the significant play could result in the components alignment causing variation. When outlining the design of mechanical components, use dowel holes are typically used by mechanical engineers as reference points to control positioning variations and so repeatable assembly quality can be attained. A dowel pin could have a smaller diameter than its hole so that it slips in freely, or could be larger in diameter so that it must be have added force applied to get it into its hole (this is called an interference fit). Steel dowel pins are set to tight tolerances, as are the corresponding holes in them, which are typically reamed to help with their installation. Steel dowel pins are often used as precise locating devices in machinery.
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