"steel" which plastically deforms and straightens the material of the blade's edge which may have been rolled over irregularly in use, but not enough to need complete resharpening. Stoning Other edges Different techniques are required where the edges are not straight. Special tools and skills are more often required, and sharpening is often best done by a specialist rather than the user of the tool. Examples include: Drill bits - twist drills used for wood or steel are usually sharpened on a grinding wheel or within a purpose made grinding jig to an angle of 60° from vertical (120° total) although sharper angles may be used for hard or brittle materials such as glass. Saws have teeth, typically splayed from the blade so that the cutting edge removes enough material to allow the whole blade to pass freely through the cleft material. Usually only the leading edge of the saw blade is sharpened. Mobile sharpening service A number of blade sharpeners operate a mobile business, traveling to their customers locations, often in highly equipped vehicles. Less common in developed nations. Still very common in many areas of the world, skilled craftsmen provide a roadside sharpening service for kitchen knives and cleavers, scissors, and sometimes other blades. They commonly have a 'round' which may include trades such as butchers or barbers some of whom, in addition to using the service for their own tools may act as 'agents' collecting instruments for the general public. Sharpeners may also have regular 'stops' in busy streets or residential areas, calling out to people from their homes or businesses using musical instruments such as handbells or pipes. The sharpener usually has some sort of mobile work bench with a grinding wheel which may be powered by hand, using a bicycle mechanism or electric motor. As well as coarse grinding, sharpeners also typically 'dress' the cutting edges with a sharpening stone or honing steel, secure or replace loose handles and generally offer advice and assistance regarding best practice. Some also sell knives and related products. Modern mobile sharpening services will travel in a Van or Bus and have a workshop inside that allows them to service the edges of different various tools and instruments. There are two major forms of sharpening or sharpeners where you sharpen as a hobbyist and "make it work" or you are a craftsman that strives to learn different styles of sharpening