CNC Milling Hold Tool
Like most tool-holding devices, drill chucks have a body that has jaws to hold tools and a shaft that locates in the spindle taper. The shaft is usually a permanent fit in the body of the chuck. Chucks are sometimes supplied with shafts already fit- ted, but bare chuck bodies normally have a short taper in the rear (often a Jacobs taper) so that a shaft can be chosen to suit the chuck taper and the mill taper, and the chuck is then permanently assembled on to the shaft. Drill chucks that screw on to a shaft are usually not sufficiently accurate for use in a milling machine. The shaft normally has a threaded hole down its length and this will be tapped for a draw bar. These are usually standard thread sizes.
Once the chuck and shaft have been inserted into the mill spindle, a draw bar is screwed into the shaft, from the top, to secure the shaft and chuck. The tool is in- serted into the chuck and the chuck key is used to close the jaws firmly. A handy variation is the keyless chuck, which can be tightened by hand by rotating a collar on the chuck. A good-quality keyless chuck is a useful item, but as with any other tool holder, a poor-quality version is a liability.
