Radius ball turner

I've been wanting to make a ball turner for quite some time. Well, this past week I finally got a "round 2 it"! My first tool holder attempt caused me to say some things, that I'm glad my son didn't hear...
...but I managed to get it right the second attempt! I first tried mounting the base to the location where the compound rest normally occupies, but soon learned that I would not have enough room, between the radius turner and the lathes center line....
On the right side of the pic, you can JUST make out the tip of the live center in the tailstock...so went back to the drawing board, and decided that I would remake the base, suited to mount on the cross slide...20190122_210105.jpg
Well, I deffinately had more clearance now, but something else hit me like a ton of bricks. I had no means of moving it forward or backward, something I didn't even consider since it was originally going to be mounted on the compound. Also, I really disliked having to use the gib from the cross slide, it was just SO oversized for this little 4" tool, so I decided to make it's own gib.

Well, this got me to thinking...there is no way that I am going to be able to keep up with that little gib, when the turner was not in use. My solution was to embed the small cut off section, that was cut in order to be able to use transfer screws to place my gib screws in the right location, with a few magnets. Viola! No losing the new gib now!

As far as for making the tool move forward and backward, I decided to make an nut that would ride on the original cross feed screw, and i was quite pleased with how well it turned out, not to mention it worked!!
After fixing those few road blocks, I decided to gun blue the toolpost, and obviously had to change the color of the lock down screws, so there would be some contrast. That process, again, turned out surprisingly well....
Only thing left to now, is mill the top of the tool holder down enough to accept an insert, and to put it right on the center line, then drill/tap the screw to hold the insert....and, oh yeah, make a brass ball for its handle!;)
Anyways, thanks for looking. It was a fun project!

Would someone be kind enough to explain what drives the choice of axis orientation for a ball turner? The two in this thread are not the same, highlighting the issue for me.
Would someone be kind enough to explain what drives the choice of axis orientation for a ball turner? The two in this thread are not the same, highlighting the issue for me.

It is mostly a matter of personal choice, I think... the one that I used in tech school 20-something years ago was more similar to SubtleHustles design. I chose to build mine more like Jim's design because I had an extra boring head, so it was a matter of 'quick and easy' for me.

Either design is very effective, both have their own pros and cons...

The major drawback for use of the boring head design is while it can do ball/convex shapes it can't do the opposite concave radii. The first design depending on where the cutter is positioned can do concave or convex. In my instance I need to do concave and convex so I'm gathering my resources to make one similar to the first design.
Very nice. A question though, when using one of these it seems the centerline of the pivot should be exactly on (and perpendicular to) the centerline of the spindle. How does one measure this to know when it is on center?