blade's path stationary while the workpiece is moved across it. This type of saw can be used to cut out complex shapes and angles. The part may be fed into the blade manually or with a power assist mechanism. This type of metal-cutting bandsaw is often equipped with a built-in blade welder. This not only allows the operator to repair broken blades or fabricate new blades quickly, but also allows for the blade to be purposely cut, routed through the center of a part, and re-welded in order to make interior cuts. These saws are often fitted with a built-in air blower to cool the blade and to blow chips away from the cut area giving the operator a clear view of the work. This type of saw is also built in a woodworking version. The woodworking type is generally of much lighter construction and does not incorporate a power feed mechanism, coolant, or welder. Advancements have also been made in the bandsaw blades used to cut metals. Bimetal blades with high speed steel teeth, including cobalt grades, are now the norm. The development of new tooth geometries and tooth pitches has produced increased production rates and greater blade life. New materials and processes such as M51 steel and the cryogenic treatment of blades have produced results that were thought impossible just a few years ago. New machines have been developed to automate the welding process of bandsaw blades as well. Timber cutting Timber mills use very large bandsaws for ripping lumber; they are preferred over circular saws for ripping because they can accommodate large-diameter timber and because of their smaller kerf (cut size), resulting in less waste. There are also small portable sawmills consisting of a shop-size bandsaw mounted on a guiding table, which are called bandsaw mills (band saw mills, band sawmills). Like chain saw mills (a chainsaw on a guiding table), they can be used inexpensively by one or two people out in the field. In a full-size sawmill, the blades are mounted on wheels with a diameter large enough not to cause metal fatigue due to flexing when the blade repeatedly changes from a circular to a straight profile. It is stretched very tight (with fatigue strength of the saw metal being the limiting factor). Bandsaws of this size need to have a deformation worked into them that counteracts the forces and heating of operation. This