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!

 

I still don’t think you can cut a half of a full radius with any tool shown in this thread. In order to make a mold to make cannon balls you have cut at least half the full radius. The hemispherical radius cutter I made will go a little deeper then half way .
I know you can cut a true radius part way into the the end of the material but not enough to get half the depth of the radius.

New item by Jim Sehr

photos.app.goo.gl

After thinking about this for a few minutes, I have concluded that we have started comparing apples to oranges...

The original topic was about ball turning tools... but I can't seem to picture in my head how your tool could turn a ball... so would it actually be a radius ball turner?

Or maybe I'm just missing something?

I'm not trying to be argumentative... just trying to connect the dots...

-Bear

 

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?

 

No I dont have any pictures but ive seen it done first hand on a HF 7x12 lathe if that makes a difference!
If you sit and think about the mechanics in making a ball on a lathe you will see that your tool needs to smoothly rotate around a "Pivot Point" (cutting edge facing inward towards the pivot point) in order to cut said ball. How far away from that pivot point you set the cutting tool will determine how large of an arc your tool can make which determines how big or small your "Ball" will be, correct? Now if you move only the cutting tool to the opposite side of the pivot point and then rotate just the tool 180° from how you had it setup for making the ball ( cutting edge facing outward away from the pivot point) you will see that the cutting edge will now face the work correctly and will rotate around the pivot making concave cuts in your work piece.

I hope that helps clear things up a bit without adding further confusion.

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

You can cut part of a radius until you get to the axis of the swing part. The only way to cut a full radius deeper than half the radius is to swing radius from inside the radius. Look at post #30 Posted by Bear.
Jimsehr

 

Imma gonna jump in here since I am a curious newbie looking to obtain (make?) a combination convex/concave turning tool. At first I couldn't conceive how a boring bar tool could do concave, but it all depends on where the pivot point is. And Latinrascalrg1 and 682bear confirm it.
In the case of convex (ball) the boring head cutter pivot axis passes through the work piece axis at the ball center and perpendicular it. If the workpiece is not a ball but a circulare plate with rounded edge, the pivot axis of the cutter is elevated (in the case of the boring bar holder) above the axis of the workpiece so that the apex of the cutter pivoting circumference coincides with the circumference of the workpiece. If the cutter pivot axis is moved further up so that the boring bar cutter is cutting in the bottom semicircle of it's arc, the apogee, and the cutter axis is tangent to the circumference of the circular plate, one gets a semi-circular groove in the edge of the plate.

So that geometry works for a wide range of stuff. Now my question is, most bending dies are fairly large diameters. How does one hold the boring bar axis high and rigid enough to cut a 4" or bigger tube bending die? And be infinitely adjustable from min to max height?

Ultimately, I don't want an array of tools, but one tool that can cut convex up to about 2 1/2" diameter and concave up to 2 1/2" diameter on the periphery of a circular disk up to maybe 8". It's a wide range, but hey. There's enough expertise here to make rocket ships and nuclear subs isn't there? Am I expecting too much? I don't want to reinvent the wheel if it isn't necessary.

DanK

 

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

 

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

Jimsehr’s super simple ball turner.

 

Jimsehr’s super simple ball turner.

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

Simple tool to cut radius in od of bar.

 

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

That type would cut into the od of a bar. But not into the face of a bar. You could cut part depth of radius into face but only till you hit shank dia of axis of cutting tool.

 

That type would cut into the od of a bar. But not into the face of a bar. You could cut part depth of radius into face but only till you hit shank dia of axis of cutting tool.

Hemispherical radius cutter to cut radius in face of part.

 

Hemispherical radius cutter to cut radius in face of part.

View attachment 393247

If your cutter is held in tool holder with 3/4 dia shank you can only plunge into face till shank hits end face of part. You would be 3/8 shy of full