I needed to make a quick ball turning tool so I decided to use my home made boring bar holder as the basis. When I originally made the boring bar holder I drilled and reamed it whilst it was held in the tool post so therefore the hole through it is "on centre line" of the lathe. The hole through the holder is 1/2" diameter. For my ball turner I machined down a piece of 5/8" dia. to be a close fit in the holder. I left a 5/8" dia shoulder at the tool end that sits back against the boring bar holder, on this end closest to operator is an Aluminium collar with grub screw to locate the shaft on this end. Now the shaft can rotate but can't move in either direction in the holder. Hopefull by next time I come to use this tool the vise grips will be replaced by a nice removable handle, sporting a ball knob of course. The boring bar holder must be able to be quickly returned to being a boring bar holder.
On the tool end I made and pressed on a sleeve of Aluminium on to the 5/8" section of the bar, this was just to give a bit more meat on the end to support the tool holder and grub screw that clamps the tool holder. The grub screw that clamps the tool holder is on the other side of the Aluminium sleeve. The tool holder shank is 5/16" dia with a 5/8" dia head where the 3/16" dia tool and M5x0.8 grub screw fit in. On this side of the boring bar holder you can see a bolt, I have a piece of fibre rod in there so I can tighten the bolt up to give a bit of friction feel. The beauty of a tool post mounted ball turner is that it's quick and easy to fit up and remove so you can swap between machining and ball turning. I also like a ball turner that can get in close to the chuck. I can counterbore the Aluminium sleeve so the head of the tool holder goes down to touch the steel part of the shaft, this will allow small balls to be made without making any special cranked down tool.
I don't have any fine adjustment on this ball turning tool but manual adjustment is quick and easy, after my final cut on the first ball I made I measured the protrusion as shown, I also measured it with digital vernier, this measurement will be used for getting the final cut on the other two balls I have to make. Once I establish the position of the centre line of the ball I put a dial indicator to the saddle so I can move the saddle away from the job for tool adjustment then return the saddle to the same place to continue with the ball turning. The ball turner might be a bit of a "rough diamond" but it does the job suprisingly well and rather quickly, I only adjusted the tool holder 4 times per ball. For steel cutting the 3/16" dia tool steel would have to be narrowed at the tip so it didn't have such a large radius nose doing the cutting.
Here is a finished ball handle. Didn't take much emery taping to get a nice finish. I could have had the ball right up to the chuck and there would have been plenty of room for the ball turner without hitting the chuck. A full size(or double size) drawing will easily give the measurement from the meeting point of the ball and plain shank to the centre line of the ball. With a bit of thinking as you go it soon becomes easy to get the right geometry. Oh, just in case you're wondering, the ball diameter is 37.5mm and the plain shank is 22mm dia.
Here are the 3 new Aluminium balls on shorter handles on the HM30 Mill/Drill. I use the mill/drill mostly for milling therefore I don't need the leverage afforded by the long handles. The long handles sometimes get in the way when doing milling work so this mod will alleviate that problem.
There you can see the difference in length. If I ever need more leverage on a drilling job I can always just put one long handle back in temporarily. The three short handles are made of stainless steel so with the shiney new Aluminium knobs the new handles look very spiffy.
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