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Ball turning jig needs modifying to fit my new lathe

I have a homemade heavy duty ball turning jig that I built years ago to fit my Graduate lathe. I wrote about it here. I’ve been converting it for use on my new Titan 315. It needed a new clamping plate and guide block to hold it in place on the bed, and the tool holder had to be raised by about 75 mm or so.

The jig is made from assorted bits of steel scrap and old machine parts. I’ve always made a point of saving odds and ends of metal that may come in handy for jobs like this. Once in a while it pays off. I picked out some likely bits and made a new clamping plate. It came from a piece of steel about 8 mm thick and 40 mm wide. I cut and filed it to fit the rebate beneath the Titan bed strips and drilled it for the retaining screw. A washer and nut beneath the plate holds the ball turning jig in place.

Ball turning jig location

To locate the jig accurately I cut a piece of birch plywood to fit snugly between the bed strips. I drilled it exactly in the middle and threaded it on the retaining screw. This positions the retaining screw, which is also the axis of rotation, directly below the lathe spindle axis, and the jig can slide to any position along the bed.

I’ve intended for some time to make a height adjuster for the tool clamp. No more shims! I decided to borrow the tool clamp from my ancient Atlas engineering lathe. This is another homemade item. It slides over a steel post and clamps to it with a pinch bolt. A jacking screw raises it to the height required. The lathe tool is held in a slot at the side.

All I had to do was make a steel post the same size to fit on the jig. With that, I could transfer the clamp back and forth as needed. I turned one end of a bit of steel bar to size in the Atlas. But my even more ancient large three-jaw chuck is in very poor condition. Because of this, I could not reverse it to make the other end match accurately. I should have put the bar between centres to turn the whole thing at the same setting.

Turning the post freehand

The chuck did the job, with help, despite its lack of accuracy. I turned about two thirds of the bar’s length to size. Then I reversed it in the chuck and turned the rest a little oversize (and noticeably eccentric). I transferred it to my four jaw chuck on the Graduate and did the rest of the turning by hand. I used a scraper, finishing with a smooth file. Back in the Atlas, I drilled a 12 mm hole through the length of the post.

To support the post I put a scrap of 40 mm steel bar in the Atlas, faced off the ends and drilled a 12 mm hole through that too, going half way from each end as I don’t have a drill long enough to go right through in one go. This made a raising block for the post to stand on. I didn’t use one single long post because I did not have a suitable bit of scrap. But if I’d had a longer bit of bar and a long drill I could have made it in one piece.

The raising block and clamping post are linked together and held in place by a length of 12 mm threaded rod. I had to file a 12 mm nut and a section of the threaded rod so they fit the small T slot in the machine slide below.

The jig is now ready for action and has a considerably larger capacity too. I use a ball turning jig often to make hemispheres that I glue together to make globes.

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