Wabble-Joint Holder for Small Drills
FAULTY alignment in drill presses is a common defect. When drilling in small jigs, this fault often causes the jig to shake or vibrate, if it is not secured to the drill press table. Clamping the jig to the table does not always provide a remedy, because the mal-alignment still exists and is apt to manifest itself in poor work and lopsided wear on the drill bushings.
The wabble-joint drill holder illustrated has been found to do good work in cases where the smaller sizes of drills are used in production drilling.
The device consists of a body, in which a set screw engages a flat on the shank of the drill, and a driver, which is formed with a flange corresponding to the body. The shank of the driver is held in the drill chuck. Both driver and body have slightly semispherical contact surfaces and are linked by headed driving pins. These are driven firmly into holes in the body and engage in radial slots in the driver head. The slots are deep enough to allow a shake of about in. either way, and the driving pins are set down far enough to space driver and body away from each other by slightly more than what is necessary to compensate for the perpendicular error. As a rule, from .005 to .01 in. will be sufficient. The slots are made wide enough to accommodate the full diameter of the driving pins, and the pins are slightly flattened sidewise to give a better contact and allow some side play in the slots.
It should be noted that the driving pin holes go clear through the chuck body to allow the pins to be knocked out or adjusted easily.
Several sizes of drills can be used in the same holder by the use of reducing bushings.
All parts of the chuck should be made from tool steel and hardened. For the body at least, it is best to use a nonshrinking steel. The drawing temperatures suggested are 560 for the body, pins and reducing bushings blue for the shank, and 450 for the working jaws.
In using the device it should be remembered that the drill press spindle assembly can be out of parallel alignment only one way. It should be ascertained which way it is out and the holder set to act approximately in the direction of the error.