Ball Turning

On Thu, 5 Apr 2012 08:25:49 -0700 (PDT), Bob La Londe


===============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.
--
Unka' George

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On Thu, 5 Apr 2012 08:25:49 -0700 (PDT), Bob La Londe

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.
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Bob La Londe wrote:

Yes, this works fine. It might be just a little slower than a CNC lathe, but will work fine.

Oh, well, that's going to be a problem with SS workpieces.
Jon
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Yeah. Makes me regret pulling the stock spindle on the Taig sometimes. Still it was only 1/4 HP so it might not have been much better.
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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:
http://www.littlemachineshop.com/products/product_view.php?ProductID=1970&category 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
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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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On Thu, 5 Apr 2012 12:52:28 -0400, "Jim Wilkins"

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?
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I tried the round cut lathe bit first. Cutting the bit was a challenge, but I eventually got one sorta-kinda radius shaped. A drop of Tap Magic on the cuter about every third pin and they cut fast. Took longer to swap pins in the chuck than to cut the radius.
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The conical grinding point I mentioned earlier can take it from kinda-sorta to very smooth, round and Sharp when the exact radius doesn't matter. If the tool is in the post ready to round the end, the die grinder holding the stone would be between the ways, pointing straight up. Keep the stone moving so the cutting edge doesn't wear a step in it.
You could mark where the cone is 1/2" in diameter and try to make the cone fit all along the cutting edge at the mark.
jsw
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