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...
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!

 

Here are few I made with a Holdridge and an offset tool holder I made to reduce the width of the "groove" behind the ball. Oh and I have done full hemispheres in the end of a bar with an angled cutter in the same tool .

 

Nice work ! I like it.

 

With the boaring bar holder mounted the same way Jimsehrs tool is mounted or how the OP has his tool mounted for that matter since they are pretty much the same (here I substituted a screw driver to play the part of cutting tool and handle which can be mounted in a few different ways,) How is this ANY Different?
View attachment 288906

Pic shows bor

With the boaring bar holder mounted the same way Jimsehrs tool is mounted or how the OP has his tool mounted for that matter since they are pretty much the same (here I substituted a screw driver to play the part of cutting tool and handle which can be mounted in a few different ways,) How is this ANY Different?
View attachment 288906

Pic shows end of boring head with screwdriver to show how radius could form radius in end of bar. Bit if you look at other end of boring bar you will see cutter will only go deep enough to to hit shank of boring Boring head. So you can cut radius depth till you hit half of boring head shank dia. You can’t make a mold for a ball.

 

Oh, re: cutting a hemispherical cavity in the end of a workpiece, I think it is possible with simple tooling. I've tried to illustrate this with a simplistic sketch showing a cross section looking downward on the action. The cutting point (short segments illustrating a 135° orientation between cutter and holder) sweeps only 1/4 of the hemisphere diameter. That means that the tool holder (longer segments) sweeps only 1/4 of it's sector also. It's easy with line segments, but I think doable with appropriately narrow tools with the appropriate overhangs to clear the edges of the cavity. A cutter held in a post won't work in any circumstance. A boring head or a swivel plate on cross feed would have to hold a cutter with offset overhang long enough to reach the cut. Think allen wrench at 135° instead of 90°. That might get sketchy if the cut is large or material difficult.

Woodworkers do this all the time with hand held tools turning the inside of a bowl.

DanK

Looking down on a boring bar trying to cut a hemispherical radius in the end of a bar the cutter has to be inside the sphere or the shank holding the cutter hits the outer edge of the bar. You can only cut deep enough to hit the shank of the boring bar. If shank is .750 dia your radius will be .375 shy of full radius.

 

Nicely done. I would like to make one of these too some day...