An adjustable broach for cutting internal keyways in small holes

摘要

I shall describe the broach I made for making a 3mm keyway in a 8mm hole. It can be scaled up or down to make keyways in other sizes or for different size holes. The finished broach is shown in photo 1. It consists of only three components: a slotted shaft, a cutting tool and a grub screw (photo 2). The shaft (fig 1) was made from a 100mm length of 8mm diameter round mild steel. A 70mm slot 3mm wide and 3mm deep was milled along the length. A 2.5mm hole was drilled through the bottom of the slot about 25mm from the end. This was tapped M3.