Single piece, simple ball turner.

[mklotz]

I've made several ball cutters for the lathe but I still prefer my incremental cutting method for non-critical (most are) spheres. If you care to explore it, download the BALLCUT archive from my page.

For the benefit of neophyte ball cutter users...

To form a proper sphere with a ball cutter, the axis about which the cutter turns must be in the same plane as the axis of the part being turned, i.e., the lathe Z axis.

If this isn't true you'll end up turning some variation of an ogive...

https://en.wikipedia.org/wiki/Ogive

OTOH, if you want to turn an ogive intentionally, the program included in my OGIVE archive will be of help.

[Ralphxyz]

Thanks Y-Geo, that is what I was referencing I see the pivot point on the Repton R1 but do not see a pivot point on the subject.

I don't even see a handle to make the pivot.

Ralph

[Toolmaker51]

Yep 23 minutes of youtube is like a semester.
There are two commercial radius attachments that have been around the longest. Eagle Rock (Shapley design) and Holdridge. Holdridge were very prevalent, still made, suited up to large lathes. The $$$ is large too, but reasonable on the auction sites. They use leverage ratio over the cutter to get smooth finish. A long handle provides control over feed rate.
The Eagle is geared and screw driven, also manually, and from an individual perspective more appropriate for personal use. Either uses simple mechanics and could be shop made with some pivot bushings or bearings and a bandsaw. Tony's is simpler yet, entirely milled.
Either way, the idea is to locate tool tip a specific distance from the axis it swings on. + is concave, - is convex.
In mating parts, I'd cut ball first, polish, and blue into a socket. You normally wouldn't seek perfect contact at the dead centers. A flattened ball contacting more surface area should wear better.

Awestruck, Marv. details for spheres and ogives!

[tonyfoale]

I'm thinking along the set-up, manipulating knee and quill Z's [prior to locking] wherein lathe that's more 'built-in' addressing centerline. Maybe better size control too? Can think of last occasion to ball turn, no-one had the lathe version, used a boring head though. Difficult to get proper finish, heads aren't too great for decent corner radii on cutters. I wouldn't spend effort on form tool even with means to generate accurate cutter, on something like a push rod.

i am still having problems following but no matter. I would not lock the quill Z because that is what gives the traverse movement along the workpiece. i have used form tools for the ends of pushrods in the past without problem but of course you have to make a different tool for each ball diameter. i am only interested in using aluminium and small diameter balls so it is not too arduous for a form tool. Anyway now that i have this direct method of turning small balls I won't be using form tools for this purpose anymore.

[tonyfoale]

I am just getting started with using a lathe and have a ball turner on my list of things to do.

Where is the pivot on you tool? Sure wish I could could see things live, posible a video of it in action would help.

Ralph,
The pivot is the compound rest pivot. It already exists and (at least in my case) was a very good fit with no discernable slop. Using that is what makes this implementation so simple. I did make a short video, I'll edit it when I get a moment and put it on You tube.

[tonyfoale]

I don't even see a handle to make the pivot.

Ralph

The compound rest is all the handle that is necessary, plenty of places to grab it. That will be clear when I post the video. I promise that it won't be anywhere near 23 mins.
There are a ton of DIY ball turners on the net, Mr. google knows about a lot of them. I expect that there are several in the archives of this forum as well, but I haven't looked. Some have low grade pivots top and bottom in a yoke construction and others have a single more substantial pivot at the bottom like this one
Free Metalworking Project Plans: Ball Turning Toolpost (Lathe, Mill) - Projects In Metal, LLC
If I were making one without the benefit of using the existing compound rest I'd make it similar to that one but I would not make the tool holder as an "L" as most do. That could be left in a triangle shape but with a concave hypotenuse for ball clearance. More metal = greater rigidity.

[tonyfoale]

For the benefit of neophyte ball cutter users...

To form a proper sphere with a ball cutter, the axis about which the cutter turns must be in the same plane as the axis of the part being turned, i.e., the lathe Z axis.
.

That could be subject to misinterpretation by some. There are an infinity of planes containing the axis of the workpiece, the definite article suggests that there is a single plane. In my initial post I specified the vertical plane which would be the most commonly used, although horizontal is often used as well. Theoretically you could use any of the infinity of planes as long as it contained both axes, which is in accord with your statement of course.
This where many ball turners fall down. Because they have no easy built-in depth of cut or radius adjustment it is common to use the cross slide for "diameter" adjustment but that moves all planes through the tool spin axis outside of any plane containing the work piece axis. Then you either end up with an ogive or the other extreme which is a longitudially swashed sphere with a flat or dimpled end. That is unless you arrange the tool setting such that both planes coincide when cutting at the desired diameter. Then you will start off with the swashed shape morphing into spherical as you approach size. Not easy to setup.
I wanted to be able to accurately turn part spheres which is why I knew that I had to incorporate a separate radius adjustment, other than manually moving the tool in its holder which would be tedious and hard to adjust precisely. The compound slide was a good answer to that problem. The cross slide is used to align the two previously mentioned planes only, and is then locked.

[mklotz]

The ball turner axis, when extrapolated, must intersect the rotation axis of the part. Is that wording more to your liking?

[Ralphxyz]

Duh OK it is "starting" to settle in. I now can understand the pivot. Now I have to work on the operation geometry.

That video sure will help.

Again thanks for posting.

Like I said I have a ball turner on my list, this is looking rather simple for even me to make.

Ralph

[Ralphxyz]

Marv I almost understand what you are saying, I need to be at my lathe to fully grasp it, I can not just picture it.
Of course I am new to turning.

Ralph