Page:Practical Treatise on Milling and Milling Machines.djvu/106

100 Number of Teeth in Cutters. This subject has been discussed at some length by various writers in books and technical papers. Standard cutters have been found satisfactory for the majority of work, and practically indispensable on some work of the lighter class, but cutters having wide spaced teeth have a marked advantage over the standard type in their ability to remove a considerably greater quantity of metal in a given time without distressing the cutter or overloading the machine. The free cutting action of these coarse tooth cutters is largely due to the fact that less cutting is actually required to remove a given amount of metal, each tooth taking a large, deep chip. This results in a considerable decrease in the tendency to slide over the surface and spring the cutter arbor. The rake and increased spiral of the teeth give a more nearly perfect shearing, rather than a pushing or dragging action. Accordingly there is less friction generated for a given cut, leaving the teeth much cooler and causing them to do considerably more work between grindings. A marked advantage arising from the free cutting action is the consumption of less power, as might be expected from the fact that there is less friction and heating. The wide spaces between the teeth allow the cutting edges to be well backed up, which was not always possible with closely spaced teeth. This increase in the strength of the teeth is much greater in proportion than the increase in work done by each tooth in removing the larger chips. Therefore the cutters are well prepared to handle deep and rapid cuts without danger of failing. In developing the line of Brown & Sharpe Coarse Tooth Milling Cutters, particular attention has been given to the angle of rake and the lead of the spiral of the teeth. After a long series of practical experiments we have adopted a type with steep spiral and consider- able angle of rake as the most economical and practical form, this type also being adapted to a large range of work which is not of the heavier class. Angle of Tooth Face. Single point tools such as those used on the lathe and planer are usually given a slight rake; that is, the face of the tool is undercut a few degrees from a radial line. A similar practice is followed in setting the teeth in the body of large inserted tooth cutters so that they have a certain amount of rake. A smoother cut is gained and less power is consumed than would be with radial