Page:Practical Treatise on Milling and Milling Machines.djvu/174

168 Gashing a Hob

While this is not strictly a gear cutting operation, it is set up and performed in practically the same manner, the principal difference being in the shape of cutter used. Many hobs are gashed spirally, and this is done in a similar way to cutting the teeth in a spiral gear. In this operation, the cut is heavy and it is advisable to use arm braces, so that a coarser feed can be employed and the work done more quickly.

The table is fed longitudinally from left to right. Oil is used on the cutter and is collected and strained in the pan below the work. An oil pump equipment can be used to good advantage on such jobs.