Ball and other shape turning using a follower and pattern

[Paul Alciatore]

Sounds a lot like what I was saying above, except I called it a shaft instead of a stylus. The basic idea was to transfer the bearings to the follower while keeping a small radius. That way the pattern can be almost any shape.

Somewhere I read about a stylus consisting of a very small vertical pin (1.0mm dia.?) with a bearing just above and one just below the pattern leaving the pin free to rotate as it follows the stylus. This, to me at least, would mimic the action of a rigid stylus against a ball bearing serving as the pattern. The pin, of course, could be larger diameter if a matching radius is present on the cutter.

It might be worth noting, in the first video posted above, that all of the workpieces produced are spherical shaped leading one to believe that the rotation of the ball bearing templates was paramount at least in the final smooth contouring passes.

The suspense is building!

[BCRider]

That would be fine if the nose radius of the cutter were something like 1mm. I wasn't thinking of it being that big. It might also be a nice way to go if I were looking at making many pieces. But I'm likely only going to ever use it a half dozen or so times.

You guys seem to be locked onto the idea that it has to be able to follow the template in any direction. That's not the goal for me. The plan is to free turn it with the X and Y used together to hog the bulk away and then to "drag" the stylus over parts of the template in a way that works with the controls and does not try to force the lead screw to turn.

Have none of you ever made a curvy part where you just manipulated the two axes at the same time? The tear drop handle I pictured earlier was roughed out and developed in that manner then cleaned up with an angle grinder with the bed and carriage all covered up. But the bulk of the shape was already there and it was more a case of blending out the grooves. For this the plan is to do it much the same but with the stylus to avoid the worst of the grooves and get the shape a lot closer.

[npalen]

I think you're on the right track and will make it work. Even though you will get a "groovy" kind of result, it should be a lot better than trying to do it without a pattern to follow. The grooves should be much smaller and easier to blend out depending on how slow you proceed.

The first video lead me to believe that you were planning on a fairly smooth finish similar to what the ball bearing produced.

[BCRider]

I think you're on the right track and will make it work. Even though you will get a "groovy" kind of result, it should be a lot better than trying to do it without a pattern to follow. The grooves should be much smaller and easier to blend out depending on how slow you proceed.

The first video lead me to believe that you were planning on a fairly smooth finish similar to what the ball bearing produced.

That's exactly my plan. Just get pretty close to where it's not going to wear out a file and 14 ft of emery strip getting it smooth. And even the guy with the ball bearing as a template still had to give the balls a final polish. I doubt that part is avoidable regardless of the rig that is used other than CNC.

[npalen]

https://www.youtube.com/watch?v=BHHhnJqdS8Q

This is not what BCRider is wanting to do but thought it was an interesting method of simple copying or tracing on a lathe. I had thought of using springs to hold the cross-slide against the template but the air cylinder has some advantages.

[BCRider]

It's not quite what I'm looking at but it's pretty nice. Thanks for that link.

I really don't want to remove the cross slide screw or nut and I'm not about to run out and shop for a spare apron, carriage and cross slide for my lathe. So rather than the air cylinder the idea is to provide the "air cylinder force" from light but steady pressure on the cross slide hand wheel.

He pointed out that he could avoid a lot of issues by doing the right hand end of the shape before transitioning to the left and center portions that where cut smaller and thus encouraged some chatter. And that's just good and proper procedure for any longer parts with complicated shapes with small portions near the chuck.

I might just have a second look at my lathe's backside of the bed and consider one of the older plans to drill and tap a couple or four accessory mounting holes in the blank area of the cross slide's far flat end that could be used for mounting a block that holds follower pin shapes. And that way I could get the template to sit back further on a rear bridge somewhat like the one shown. It would avoid any limits on the work diameter and it would get the template and little table away from the swarf.

But either way I do want to be able to bring the tail stock in for support on longer items.

[Paul Alciatore]

Hey, I am sure you will do it whatever way that works for you. I was just daydreaming about the possibilities of the idea. It intrigues me.