Ball Turning

How exact?

If it didn't have to be too terribly precise, I'd figure out how to make an end mill with a hemispherical "innie", 1/4" in diameter. Then I'd push those dowels into it.

If that wouldn't cut it for fit or finish, I'd make a cutter with a circular 1/4 turn, 1/4" diameter cutout, and individually turn each dowel.

Or, I'd make or obtain a spherical turning tool, and use that.

Or, I'd make a drawing, and give it to a company that has an NC lathe...

Back when people still knew how to use speed lathes with tool rests (like the ones on woodworking lathes), freehand turning, there was a common tool for that work.

It's a flat piece of HSS bar, maybe 1/8" or 3/16" thick, with a hole drilled in one end, countersunk to leave a sharp, circular cutting edge on the opposite side of the bar. The hole is somewhat smaller than the diameter of the ball or hemisphere you're going to turn. I don't know if there's a formula for the relative hole size. The cutting edge just shaves a thin chip off of the ball as it develops.

If you want to test your skill, try it sometime. It's not for the faint-hearted, and make sure your insurance is paid up. But it does work once you get the hang of it. Make sure it has a long handle and that the rest is set close to the work.

My take....

Accuracy / finish?

Stick the dowels in a battery drill & do them on a linishing belt. If needed make a jig / mechanism to assist in getting a nice hemispherical end on them.

Probably I would just make them from scratch by running 12ft lenghts of bar stock through a swiss machine.

Or, grind a form tool and mount on the lever cross slide of a 5c chucker.

Bob La Londe wrote in news:6ea1cfb9-1965-4cdf- snipped-for-privacy@2g2000yqk.googlegroups.com:

Take an appropiate radius corner rounding end mill, and use a collet tool holder to hang onto it on the lathe. Rotate it and adjust the height so you can use it as a form tool.

Doug White

With what I have available for machines, and assuming the finish and accuracy of the sphere is not very fussy: a combined form/cutoff tool in a lathe with a lever collet closer. Angle the cutoff edge to leave a tit on the square end of the pin if you need to minimize the tit on the spherical end.

Set a stop for length, pull the stock to the stop (no need to stop the spindle), cross feed to cut, repeat. Hopefully you can use 303 SS or one of the free machining 400 series alloys.

Assuming you have a lathe then you can buy a corner rounding endmill, as others have suggested, or you can make a form tool out of HSS. Making the form tool is pretty easy. Put Dykem or similar layout ink on the tool and scribe the form. Rough out the form with a grinding wheel and finish the form using a brass rod turned to the proper diameter charged with lapping compound. I use diamond lapping compounds but Clover compound works well too. Eric

No. They don't need to be terribley accurate. This is just to make the non press fit end of alignment pins a little faster to start. They do need to be pretty and smooth though.

My thoughts were to make a lathe bit to round or cut and round out of HSS. Past experience has shown I am not all that good at grinding lathe bits, but I did say it doesn't have to be too terribley accurate.

A CNC lathe would be the easy answer for starting with long stock. Two problems. I have about 400 pins already, and that will last me a while. I don't have a CNC lathe... or do I?

I thought about using a round over end mill. Either by chucking a rotary tool up in my tool post. (A mount to do this is on my to do list.), or by mounting the pin in a vise vertically and circling it with the round over mill on one of the mini mills. I had not thought about using it in a fixed configuration, but I can see how it would work.

A ball turner was on my consideration list. I can make either a stacked bearing type or a wishbone type. I think I have a tube of cheap all stainless skate bearings a buddy of mine gave me around somewhere I could use for the stacked bearing type, and I think I have some bronze sleeves I could use for the pin bushings in the wishbone type. My thought on that though are because of the lack of rigidty in my lathes (the 8x18 is better) and the additional flex of the ball turner itself those would require light cuts, which is both time consuming and a bad idea on stainless.

I had not even considered using a concave hemispherical end mill.

I had not even thought of (or new about) the free hand method using a drilled piece of HSS. While intellectually it intrigues me, on a practical level it scare the crap out of me. Kinda like metal spinning with a 4 or 5 foot long lever/shaping bar. LOL. Awesome to watch somebody else do.

The battery drill method would make them roughly uniform, but I think it would take a while. It would work. If I were making just one I might do it that way. Inpsite of my poor skills at making lathe bits, I am pretty decent at that type of "freehand" work.

Cutting them from bar stock makes perfect sense. 12' probably not so much in my shop with the equipment I have and the way its layed out in the shop, but cut down to 2-3' with a wood notch rest sitting on the next bench over to prevent whipping of the free end would work. That is probably what I will do in the future. I can also select free maching alloys of stainless for it then. It would also allow me to more easily customize my pins using some other ideas I have for making them easier to seat and keep straight on the press fit end. Being somewhat frugal (ok cheap) I'ld like to save the box of pins I already have first.

Here are the solutions I am going to try in order:

1. Put the dowel in the spindle of one of the mini mills. Put a small vise on the table. Clamp a lathe bit in the vise. Cut the end of the dowel just like on a CNC lathe. For the precut pieces I have this should be fine if the collets will hold them well enough and leave out enough to cut. (I'll try it with the cabinet doors closed, LOL) For using this method for longer stock I would need to put the original spindle back on the Taig. (it is hollow and I can feed stock through it).
2. If one doesn't work, I will already be setup for (2.) Use my mini mill to cut a lathe bit to shape. Do them on the lathe.

Current headaches with both of the methods I plan to try first. My spindles are really way to fast for this type of work. I do have a PID speed controller sitting on the shelf for one of them that could theoretically get me down to 5-6000 RPM (realistically more like 8000) and still have good power since the PID will automatically compensate for any drop in RPM. Still awfully fast, but I might be able to make it work.

For the future... I am accumulating parts to do a CNC conversion on the 8x18 anyway, which would be the best tool for the job of those I have as far as just making the cuts at the right speed. The 7x14 would do it, but now that I have it "pretty good" I want to keep it manual just for those occassional quick small pieces that are easier and faster to do manually. Becasue it has a 4 jaw it will be the one I use if I cut the dowels manually with a self cut lathe bit. I think it will hold the piece better.

1. Use a

Bob La Londe fired this volley in news:8919567c- snipped-for-privacy@l30g2000yqb.googlegroups.com:

Bob, you have a CNC lathe. It came as part of your mill.

Chuck the work in the spindle. Mount a tool on the bed. Turn away!

LLoyd

c-

Answer 1. Above. LOL. Thanks Lloyd.

Classic method(besides Ed's), is to use a collet with a stop in the lathe and a pivoting tool rest. This last can be just a bar with a pivot held by some means on the compound rest up to an elaborate gear driven C-shaped holder in a half-gimble. Here's one sort:

Most of the ones I've seen have the pivot point with a vertical axis, you can offset your pivot from the workpiece's axis for different shapes that way. Can go from a complete sphere to just a spherical corner break.

Advantage of that method is no special tool grinding needed, just stick in a HSS tool with a standard tip for the material and have at it.

Ball-turning attachments are perennial articles in the home shop magazines.

If you're really going to go into production, use the form tool/ milling cutter ideas.

Stan

No. They don't need to be terribley accurate. This is just to make the non press fit end of alignment pins a little faster to start. They do need to be pretty and smooth though.

My thoughts were to make a lathe bit to round or cut and round out of HSS. Past experience has shown I am not all that good at grinding lathe bits, but I did say it doesn't have to be too terribley accurate.

I ground concave quarter round lathe bits with a tapered cone wheel in a die grinder. It automatically gives a relief under the edge.

jsw

[Snip list of rounding methods]

I don't see a good reason to round the ends for that purpose. A chamfered or conical end would be easier to cut with good finish than a hemisphere, and probably better as an insertion aid.

"Stanley Schaefer" wrote

driven C-shaped holder in a half-gimble. Stan

I chucked the top half of the compound in the 3-jaw and marked the center of rotation, which for my lathe is on the top slide close to the tee slot with the compound fully back. I can turn a small convex radius by swiveling the compound, with a bit in a lantern holder.

jsw

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Why not just cut a heavy chamfer? Curves are always difficult to machine in a manual machine. A straight chamfer can be cut many ways and should be cheaper/quicker than a radius.

One thought is an adaptation of a screw machine or turret lathe tool that did this operation, called a box tool.

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Store bought solution or roll your own based on the picture. Used regular straight ground lathe tools.

Yeah, they're nice (I have one that my uncle made, which I used only once, on aluminum), but not for balls with 1/4" diameter.

Someone might have mentioned this, but, FWIW, my approach would be to rough it out with a file and then plunge in a skiving tool (flat-topped form tool; skiving tools often don't have relief, but it would need relief in this case) to finish it. The skiving tool would have a cutting edge shape that is 1/4 of a circle.

I have not done with with stainless but I've done it in brass, where it works great. The flat-top tool is essential in brass, because that much cutting edge cutting into brass is likely to dig in and put a heavy load on everything.

Why not just rotate the non locked compound as your ball turning apparatus? Use a collet in the spidle, use the tool mounted to the compond to stop the rod, clamp the collet and rotate the compound rest

90 degrees clockwise to generate the hemispherical surface (you need to set the tool bit back of the center of rotation of the compound by the rdius of the rod and exactly on center height).Clear as mud?

Back in the day it was quite common to see a "turning tool" in a machinist's tool box. Usually used to make ball ends for vice handles and such non-precision things you just put the tool holder in backwards for a tool rest and went at it - about like turning maple on a wood lathe.

Mine was about 12 inches overall made from a length of 3/8th drill rod with a spiffy aluminum handle I turned up one lunch hour and shrunk on. But really just a steel rod with the end ground flat with a bit of an angle for clearance, and hardened.

Or use a form tool with an extended lip used as a cutoff tool. Probably grind one up out of HSS in 20 minutes.

-- Cheers,

John B.