Jim's truly simple ball turning tool

Shotgun said:
Then I'd take the "extended" piece of the design, and screw it's base to the t-nut.
Click to expand...
That should work. Doesn't seem to reduce the part count though (you're just using your existing tee nut and have to make another piece to bolt to it).

Note that the original version of the design didn't have as much of a projection, and it wasn't stepped down. That meant the top of the tee base had to project above the top of the compound for the puck to swivel. With the step, this is no longer necessary, so you could use an existing tee nut.

The problem with using the pivot of the compound itself rather than an auxiliary pivot is that you have to get the center of rotation under the center of the ball for the final pass. Without an auxiliary pivot point, that requires a LOT of stick out (and subsequent chatter).

Cap screws work just as well as set screws to lock the tee nut, as does clamping from above. You just need clearance so the handle can swing ~180°.

Honestly, the set screws pushing up rather than clamping the ledge of the tee is more of a theoretical concern than a practical one. You'd really have to gorilla the screws to have any risk of damaging your compound.
 
I never thought I’d run out of small diameter end mills …

But I just discovered that HHIP on Amazon has 3” lengths of 3/16” dia HSS rods for a little over a buck apiece. Since I’ve got prime it’s a no brainer.

I usually prefer HSS to carbide anyway. Less brittle, so less chance of chipping/snapping from my clumsy hands, and easier to grind.
 
Okay, I finished making another one to the drawing (with a 3/16" dia cutter this time) and several pucks.

I was happy to prove that it cuts just fine without any soft of retainer for the puck, but I discovered that if you aren't careful you can get chips under the puck which causes rocking. So I'm going to add some sort of retainer mechanism on the bottom anyway (likely just a washer and a screw). I'll want some way to adjust the clamping pressure that doesn't loosen up in use.

I made my pucks out of some 1 3/8" 12L14 I had on hand. That's really only big enough for about a 7/8" ball (because you need at least a few threads of engagement for the set screw in the side). I might still make one puck large enough for a ~1" ball with the compound mount, but any larger will require a different base.

The balls on my mill vice handles are about 1" dia. That's about the largest I'll ever want to make, I think. Most of the time 3/4" and smaller will be fine. Anything smaller than 1/2" is definitely easiest to make with a form tool.

With 1/4-28 set screws and a long tee-handle driver I don't think there is ANY worry of putting undue stress on the compound ledge — the driver would break before the compound. Using the short leg on a standard driver might be an issue if you really gronk on the screws, but ... don't do that, there's no need.

The only other aspect of the design that I might change is drilling the hole for the set screws straight through. That seemed easiest, but in hindsight since the cross hole for the cutter is about the same diameter, it doesn't leave much meat behind the cutter. If you grind the cutter too short so that it's not bearing top and bottom, it might be a problem. You want to drill and tap the hole for the set screw before drilling and reaming the hole for the cutter, to ensure the hole for the cutter is clean without burrs, but I now think it's best to only drill to about the midpoint of the cutter hole (and use a dog point set screw).

Posting this in case anyone is actively building to my drawings.

I've now made two prototypes. Third time's the charm (or is it "three strikes and your out"?).
 
Rex Walters said:
I never thought I’d run out of small diameter end mills …

But I just discovered that HHIP on Amazon has 3” lengths of 3/16” dia HSS rods for a little over a buck apiece. Since I’ve got prime it’s a no brainer.

I usually prefer HSS to carbide anyway. Less brittle, so less chance of chipping/snapping from my clumsy hands, and easier to grind.
Click to expand...
This would be an excellent application for broken drill bits and end mills.
 
Shotgun said:
This would be an excellent application for broken drill bits and end mills.
Click to expand...
That’s what I meant! I’ve run out of small broken end mills somehow. I must have tossed a few.

3/16 dia is a nice size. Small enough that there is never too much cutting force even when half the cutter is buried in the work, small enough that you don’t need too big a diameter puck.

I’ve made a few more small changes:
  • A retaining washer and cap screw on the bottom make a big difference in feel (much more solid). I even figured out a neat trick for getting the feel chef’s kiss perfect (more later).
  • I’ve decided on just one hole for the cutter per puck. The pucks are pretty easy to make, and you can pre-make blanks. The extra hole for concave cuts is just a place for swarf to collect. Since there are still two holes for the handle, one puck can still create both concave and convex cuts anyway (albeit at different radii, differing by the diameter of the cutter). Also, labeling the pucks is easier with just one cutter!, and you can leave a dedicated cutter pre-set at center height in each puck.
  • The threaded cross hole for the set screw should only go to the middle of the cutter hole as I wrote previously.
 
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I've just posted the first two parts of my build series for beginners on my blog.

I've also made several updates to the 3D model and dimensioned drawings. The last page of the latter will be particularly helpful to anyone attempting to build one of these.

I'll update the top post with these links as well.

Please let me know if you do end up building one of these! It's a useful tool and quite fun and satisfying to use.
 
Rex,
Thanks for the detailed drawing.
This now makes sense. The reamed pin or pilot would allow for rigid freedom of rotational movement.
 
Thanks, Jeff. I’m pretty happy with those drawings.

A smarter man would have waited until he completed sheet 4 to make his pucks. I thought “Nah, it’s easy math … I’ll just do it in my head and build them on the fly”.

One thing to maintain your sanity: label them with the radius sizes, not the ball diameter. Same way radius gauges are labeled. A guy I know kept mixing up radius and diameter while doing math in his head.

Anyone want some pucks to turn effectively random ball sizes?
 
I've got a bunch of pucks from making the bases for the shared indexer project, and then making them again after screwing them up the first time. 3" and 2" diameters. I know what to do with a bunch of them now.
 
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