Correct head shape for the ball turning HSS bit

[WobblyHand]

What does the actual cutting tool bit look like?

From what I see, it is just a round piece of HSS rod, stuck upright in the swivel base below. The tool height is set to the centerline of the lathe. I would think the rod face is ground flat, but there seems to be a slight bevel in the last video. That could be my eyes playing tricks on me, though. @Jimsehr, how did you grind the tool?

 

[Jimsehr]

From what I see, it is just a round piece of HSS rod, stuck upright in the swivel base below. The tool height is set to the centerline of the lathe. I would think the rod face is ground flat, but there seems to be a slight bevel in the last video. That could be my eyes playing tricks on me, though. @Jimsehr, how did you grind the tool?

Wobblyhand
You are right the tool is either hss or round piece of carbide. You could use a shank of a broken tap if you wanted. To make what ever size radius you want
you ream center of base on mill then move base over half distance of radius plus half dia of what ever you are using for a cutter. I just used a piece of aluminum for the base and it turns on a Allen bolt. I did not worry about wear as I can make a new base guickly. And I don’t think a home shop is going to make that many balls anyway. My design lets me turn the balls almost all the way around. Many of the ball turners will only let you cut about half way around the ball. I was told the design would not work but the video shows it works. The tool will not face the end of stock because there is no clearance . I know I could make a tool with clearance but I don’t have to. The top of tool should be dead true to center. But all radius tools should be to turn a true radius. To sharpen tool you just put a flat edge on the end of your round. You can give it a little top back if you want. I have made about 50 balls with tool and never sharpened it. Of course I’m not cutting Inconel . You can make a base with many different size radius as you want. All you have to do is move the cutter to a different hole. The first radius turner I made I called it Jim Sehr’s super simple ball turner. One thing I do is drop a bit of oil between base and bottom plate.

 

[WobblyHand]

Wobblyhand
You are right the tool is either hss or round piece of carbide. You could use a shank of a broken tap if you wanted. To make what ever size radius you want
you ream center of base on mill then move base over half distance of radius plus half dia of what ever you are using for a cutter. I just used a piece of aluminum for the base and it turns on a Allen bolt. I did not worry about wear as I can make a new base guickly. And I don’t think a home shop is going to make that many balls anyway. My design lets me turn the balls almost all the way around. Many of the ball turners will only let you cut about half way around the ball. I was told the design would not work but the video shows it works. The tool will not face the end of stock because there is no clearance . I know I could make a tool with clearance but I don’t have to. The top of tool should be dead true to center. But all radius tools should be to turn a true radius. To sharpen tool you just put a flat edge on the end of your round. You can give it a little top back if you want. I have made about 50 balls with tool and never sharpened it. Of course I’m not cutting Inconel . You can make a base with many different size radius as you want. All you have to do is move the cutter to a different hole. The first radius turner I made I called it Jim Sehr’s super simple ball turner. One thing I do is drop a bit of oil between base and bottom plate.

Thanks for the explanation, very helpful.

I was thinking of making one for my mini-lathe. Guess I'd need to mount it to the top of the cross-slide, as my compound seems to be too high. Looked at using the swivel disk that the compound mounts to, but there's too much play there (about 0.015 - 0.020") to be the axis of rotation. Either I could make a new better fitting swivel plate, or I could make an entirely new plate that bolts to the cross slide (or swivel plate). Then everything would mount to the plate. There's some other possibilities, but I need to think them through.

How do you adjust the radius of the cut? Are you using fixed holes, or a sliding tool? Don't recall seeing an obvious method of positioning the tool radial position. My apologies, Jim, you explained it above. Guess, I'm still not understanding it.

 

[Jimsehr]

Thanks for the explanation, very helpful.

I was thinking of making one for my mini-lathe. Guess I'd need to mount it to the top of the cross-slide, as my compound seems to be too high. Looked at using the swivel disk that the compound mounts to, but there's too much play there (about 0.015 - 0.020") to be the axis of rotation. Either I could make a new better fitting swivel plate, or I could make an entirely new plate that bolts to the cross slide (or swivel plate). Then everything would mount to the plate. There's some other possibilities, but I need to think them through.

How do you adjust the radius of the cut? Are you using fixed holes, or a sliding tool? Don't recall seeing an obvious method of positioning the tool radial position.

I have made the base with a sliding tool holder. But I have also made the base with fixed holes for different radius. And as I mostly know what radius I want the fixed radius tool is used the most.
Jim Sehr

 

[WobblyHand]

I have made the base with a sliding tool holder. But I have also made the base with fixed holes for different radius. And as I mostly know what radius I want the fixed radius tool is used the most.
Jim Sehr

Thanks for your prompt answer and help! You have been very patient with my questions. Think I know enough to proceed.

 

[Jimsehr]

Thanks for your prompt answer and help! You have been very patient with my questions. Think I know enough to proceed.

Good luck with your build. You might get some more ideas by looking at some of the stuff I have done. Google Jimsehr machinist

 

[Maplehead]

So your tool is just a carbide or HSS rod with a flat top? Basically a rod that has been faced?

 

[Jimsehr]

So your tool is just a carbide or HSS rod with a flat top? Basically a rod that has been faced?

That is true. I was told it would not work but if you look at the video it does. I was also told my hemispherical internal radius tool would not work. With a regular ball turner you can not put a full radius into the face of bar . Your cutter has to be Inside the radius to do that.
Jim Sehr

 

[Maplehead]

That is true. I was told it would not work but if you look at the video it does. I was also told my hemispherical internal radius tool would not work. With a regular ball turner you can not put a full radius into the face of bar . Your cutter has to be Inside the radius to do that.
Jim Sehr

Hi Jim
I have a few questions.
So I made a new ball turning attachment this weekend. It works better and faster than my previous design, (as it's much like yours), but it's still no where near as fast and clean as yours. My practice ball was just half a sphere on 3/4" round bar. I set the cross slide so that the bit was dead center with the rod. I also parted out a gap 3/4" in from the end of the rod. (BTW, it parted as quickly and easily as your parting did in your video. No idea why.) I then marked 3/8" in from the end of the rod with one of those wheel marking gauges. So here's the things I noticed that I don't like:
1. I take .005 cuts as more doesn't work well. So it's slow going.
2. The cuts are never smooth. It's like a bunch of lines rather than a smooth finish.
3. When the bit got o the end of the rod, effectively completing the hemisphere, I did not reach the 3/8" mark. I came up short. Why?
Any and all help and/or suggestions you can give for a better ball turning attachment is greatly appreciated.

 

[jwmelvin]

2. The cuts are never smooth. It's like a bunch of lines rather than a smooth finish.

Your tool looks to have a sharp nose radius, very different from a vertical piece of round HSS. Try a rounded nose. (It also looks to have negative top rake at the tip, which can’t be helping; I suspect that’s what limits you to 0.005” cuts.)