TOOLS – A GRADUATED ROTARY CHUCK
Mark comes up with a simple solution producing a useful workshop tool.
Here’s a little gadget that I have been intending to make for some time – A simple graduated rotary chuck, for drilling on Pitch Circle Diameters, milling squares, hexagons, whatever. We had a similar device, probably also homemade, in the workshop where I used to work at Leeds University and I found it very useful.
I think the photos are fairly self-explanatory, I didn’t bother to make any drawings but just made it to suit the pieces of steel I had to hand at the time. The graduations are provided by a modified plastic 360-degree protractor, which was stuck in place with epoxy and also clamped by the chuck as it bolts down.
Note the brass pads under the clamping screws; these are to prevent bruising of the chuck spigot which may make it stiff to turn. The chuck itself is 3¼ inches in diameter, to give you an idea of scale.
The chuck spigot is only fastened to the base by the clamp screws; loosen these and the chuck assembly can simply be lifted off. Therefore I wouldn’t use it for heavy-duty milling, but this does mean that a workpiece can be removed from the drill or milling machine while it is still clamped in the chuck and offered up to a mating component, then returned to the milling machine without losing its location.
For a job such as rounding the ends of coupling rods for example, where the workpiece needs to rotate to provide the feed, I would use a beefier rotary table so there would be no danger of the milling cutter snatching and trying to lift the whole thing off its base.
This device can of course be fastened to an angle plate for horizontal work, or even an adjustable one for drilling angled holes and the like. The dimensions aren’t critical;
“A workpiece can be removed from the drill or milling machine while it is still clamped in the chuck...”
the only points to pay attention to are to make sure all diameters of the chuck spigot are concentric so as not to introduce any run-out, and that the spigot is a nice smooth, shake-free fit in the base.
The photos show the component parts laid out, assembled into the complete unit, and in use on my milling machine, making some funny little triangular pipe flanges for the water feeds on my 5-inch gauge Britannia locomotive.