Creating a Sphere on the end of a shaft

[Shotgun]

But can your compound go far enough past the axis that you can turn the cutting tool around and point it back at the axis.
@RJSakowski , all due respect, but that is the way I had to do it on an Atlas-Craftsman 12x36 that I used to own. Like @Inferno , I couldn't back up the cross-slide enough, so I went the other way, turned the tool around, and flipped it over.

 

[RJSakowski]

But can your compound go far enough past the axis that you can turn the cutting tool around and point it back at the axis.
@RJSakowski , all due respect, but that is the way I had to do it on an Atlas-Craftsman 12x36 that I used to own. Like @Inferno , I couldn't back up the cross-slide enough, so I went the other way, turned the tool around, and flipped it over.

I see what you are doing now,

I had the same issue cutting balls with the 6 x18. I rotated the compound so that the crank was at the rear of the lathe.

I think you meant the compound rather than the cross slide in your last sentence. To cut a spherical surface, the pivot point has to be directly under the spindle axis. If the compound pivot is being used, the cross slide is fixed.

 

[BGHansen]

Thanks Bruce - I may end going with a pre-ground tool. For what they cost you can almost buy one of the cheap ball turners on amazon - do you have any experience with them. I've read some reviews that indicate they are not good with steel? Also - I would really like to get my head wrapped around the swiveling compound technique.

Rick

I have a relatively high end Holdridge radius attachment so I've not looked at the Amazon ones though others here have had good luck with them.

Bruce

 

[Inferno]

But can your compound go far enough past the axis that you can turn the cutting tool around and point it back at the axis.
@RJSakowski , all due respect, but that is the way I had to do it on an Atlas-Craftsman 12x36 that I used to own. Like @Inferno , I couldn't back up the cross-slide enough, so I went the other way, turned the tool around, and flipped it over.

I see what you're getting at now. Basically flipping the direction of the part on the axis. It would be tricky but it might work.

 

[Rick_B]

Thanks RJ - that kind of helps but my ignorance/lack of experience is showing gain. So let"s say I have a 1/2 diameter shaft in the lathe. I also have an Aloris tool post mounted in the compound T slot. Am I turning the compound so the tool tip is pointing directly at the center of the work piece (tool is in line with the head stock spindle). then I would use the cross slide to move the tool so it is aligned with the work center point. Then I would back up the compound so the tool is behind the pivot point (pivot pint being the center of the compound) and that all should give me a convex arc? I'm betting I got this all wrong because I can't visualize how I can get the tool back far enough. I think I said above that I have a Clausing 12" lathe. Feel free to slap me around for being dense .

Rick

 

[Jimsehr]

I would like to put a sphere/radius on the end of a 1/2" diameter shaft using a 12" lathe. I know there are a few different ways to do this but I am specifically interested in a method I have heard about that involves turning the sphere using the swivel function of the compound rest. Has anybody ever heard of that? If so, can you point me to something that goes through the set up?

Thanks
Rick

I have made many spheres on shafts. I have made a 3/8 ball in a 5/8 ball in a 7/8 ball in a cube . I have made a ball in a ball. I have done what you want spinning the compound. It’s a pain to set up.
I have made super simple ball turners and cut steel with ease.
I can hand grind a radius tool on my bench grinder and lap to size on my lathe within a few thousands. Look closely at my avatar .

google Jimsehr machinist to see results.

 

[Parlo]

Make a radius form tool from high speed steel. Rough grind the shape and finish off with a carbide end mill of the correct radius.

 

[homebrewed]

so how did you machine the knob?

Rick

I did it this way:



I bought the ball turner from Little Machine Shop. It required an adapter plate, which I had to make, to get it to the correct height. The tool mounts where the compound slide normally is installed. This is problematic because the only way to advance the turner into the work is by turning the carriage wheel -- not a very accurate, nor stable, approach. The ball turner was pretty inexpensive and illustrates the old adage "you get what you pay for".

To address this problem I did two things. First, I added a hand crank to the leadscrew so I could advance the carriage by engaging the half nuts and turning the crank. The LS is 16TPI so it's a bit coarse, but OK for decorative stuff like this. Second, I added a DRO to the Z axis of my lathe. I mounted it on the back side of the lathe.

The fine feed gearing for my lathe is rather coarse so I often use my LS hand crank when I'm doing the final passes on a piece. Kind of a bonus. For safety's sake I _do_ remove the crank when I'm threading.

 

[Rick_B]

Well I spent sometime today playing with the compound on my lathe and I have to admit I just don't get what you folks are talking about. I guess I don"t understand what you are talking about when you say pivot point and getting the tool behind the pivot point. I realize there are other ways to skin the cat but I wanted to try and understand this particular one.

Rick

 

[Jake M]

I would like to put a sphere/radius on the end of a 1/2" diameter shaft using a 12" lathe. I know there are a few different ways to do this but I am specifically interested in a method I have heard about that involves turning the sphere using the swivel function of the compound rest. Has anybody ever heard of that? If so, can you point me to something that goes through the set up?

Thanks
Rick

This absolutely can be done, HOWEVER it is dependent on your lathe. You have to be able to solidly mount a cutting tool, so that it's cutting tip is pretty near the center line of the compound rest's travel axis. (That's not "required", but for a radius that small, it's gonna need to be pretty close. The radius gets big, fast as you move away from the center the pivot action.). Next, you have to be able to retract the compound so that the most extreme point of the cutting tip is BEHIND the pivot. In your case, half inch rod, and assuming the cutter is dead nutz lined up to the pivot, you'd need to be a quarter inch behind the pivot to get the quarter inch radius/half inch "dome" you're looking for. And you're going to need to adjust said compound rest's locking mechanism as tight as it can possibly be, while still being able to easily and SMOOTHLY rotate it. And last, you've got to driver the CROSS slide until the pivot for the compound is lined up dead center to the lathe spindle centerline.

as @woodchucker said, It's dead easy on a South Bend 9 with a rocker post, except that it's easier to ditch the tool holder and shim the tool bit directly into place. On other lathes I'm sure it's possible, and some, it's quite probably not possible...

The key is, on any lathe, (and while the general concept is the same, EVERY lathe is going to be different), to put the tool bit in a position where swiveling the compound rest makes the tool follow an arc. The tool WILL follow a circular arc anywhere that you put it. Putting it closer to the work than where the pivot is will make a concave surface. Putting it behind the pivot will make a convex surface.

The absolute best advice I can give you is to set up a tool as best as you can by these directions (or any on the web), put a piece of similar stock in the chuck, move tool, cross slide, and compound into somewhere close, and just go through the motions. Don't even turn the lathe on. Pretty quick, you'll see where you need to be. That's kind of the best way anyhow... You can find "some" datums to help you dial in on where you want to be, but you WILL be using the eyeball method to know when it's just right. It does work, and "can" work well... But you can't really dial indicate this sort of shenanigans that you're arguably probably not supposed to be doing anyhow.

Oh yeah... If you're not able to point the tool "straight" to the point you want it to be, if it has to come in at some angle? You can always grind the point accordingly, so the cutting geometry is presented properly even if the tool points off at a strange angle from it.