Ball and other shape turning using a follower and pattern

[brian Rupnow]

For many, many years (and maybe even yet) they had a tracer lathe set up tracing the shape of a coke bottle and reproducing it in aluminum at the Toronto museum.---Brian

[BCRider]

Won't you need more Z axis distance between the cutter and stylus? Maybe I'm missing something there?

Not sure what you mean by "Z axis in the case of a lathe. If you mean height in this particular case to keep the bits and pieces smaller I'm choosing to locate the template mounting table at around 1.8" below the spindle axis. It would be easier if it were a little higher and it would still clear a 1.5" diameter stock piece. But as it is I expect the flat table and template to be a bad chip and curlies collector requiring frequent brushing to stay reasonably clear. But for as little as this template turning setup will be needed I'm willing to live with that.

And that's a big part of why I like this seemingly minimalist approach. It'll be quick to make, not take up much stock and easily stored away. All major pluses for a setup that might get used once every 4 or 5 years to make very few parts each time. And that would be why I don't really want to make it up as a big bridge like structure spanning a big part of the back of the bed.

[Paul Alciatore]

Or, conversely, the tool's tip can have any radius or other shape as long as the follower has the same shape.

While watching the video I realized that if I wanted the ball to meet a cylinder shape (a handle) with a radius between them (a fillet) all that was necessary was to grind the tool with that radius and use a matching follower. The ball would still be a good match to the bearing's diameter but the tool would leave that fillet between the ball and whatever is to it's left.

And I wonder if the follower could be fitted with a small ball bearing so it could easily follow any shape. And grind the tool to the same radius as that small BB.

Or, here's an idea for a small diameter follower: a vertical shaft which can be any desired diameter supported by two ball bearings above and below the pattern. The pattern could then be sheet metal with any shape. And the tool would have the same tip radius as that of the vertical shaft. So you could use a 1/8" shaft or even a 1/16" or a 1/10" one. The exposed length of that vertical shaft does not need to be very long. If the sheet metal pattern was 1/16" thick, then the two bearings could be just that far apart with a few thousandths more for clearance.

Just some wild ideas that came into my head while watching the video.

These work well but keep in mind that the tip radius of the follower and the tool need to be the same. Otherwise the part will not exactly match the pattern.

[npalen]

Not sure what you mean by "Z axis in the case of a lathe. If you mean height in this particular case to keep the bits and pieces smaller I'm choosing to locate the template mounting table at around 1.8" below the spindle axis. It would be easier if it were a little higher and it would still clear a 1.5" diameter stock piece. But as it is I expect the flat table and template to be a bad chip and curlies collector requiring frequent brushing to stay reasonably clear. But for as little as this template turning setup will be needed I'm willing to live with that.

And that's a big part of why I like this seemingly minimalist approach. It'll be quick to make, not take up much stock and easily stored away. All major pluses for a setup that might get used once every 4 or 5 years to make very few parts each time. And that would be why I don't really want to make it up as a big bridge like structure spanning a big part of the back of the bed.

The Z axis is always parallel to the spindle whether it is a milling machine or a lathe With that said and some further thought, I don't see the problem now that I had envisioned. (The horizontal distance between the cutting tool and the stylus)

I ran across this video while surfing the tube and the part(s) being made are remarkably similar to the hand crank you are wanting to produce:
Its basically free hand tangential metal profiling..

https://www.youtube.com/watch?v=BDtrDv6uZTs&t=752s

[Paul Alciatore]

I also learned typing in my HS years, but I didn't have your option as my HS was all boys.

My parents had a classic Underwood manual typewriter and it came with a book on teaching yourself to type. So that was one of my HS, summer projects: teaching myself to type. I think I improved in college when I had to type papers but only became really proficient in the Army where I moved up to the IBM electrics with the type balls. Great machines. Now if I could just learn to spell. And yes, I often edit. That last sentence was an edit.

My wife also had an Underwood but I don't know what happened to it. Wish I still had it for no other reason than just to show it off. Under a clear cover in my office or den. Oh well, too much clutter anyway.

I also seem to just click out the words, perhaps too many on occasion.

JR, I took typing in high school Grade 9 as it had the most girls out of all the electives. And while that was OK it turned out that typing ended up being about the best thing I learned out of high school. I can rip off long posts like these in just a couple of minutes. Editing and clarifying takes longer than the actual typing. So I do tend to ramble at times....

[BCRider]

The Z axis is always parallel to the spindle whether it is a milling machine or a lathe With that said and some further thought, I don't see the problem now that I had envisioned. (The horizontal distance between the cutting tool and the stylus)

I ran across this video while surfing the tube and the part(s) being made are remarkably similar to the hand crank you are wanting to produce:
Its basically free hand tangential metal profiling..

https://www.youtube.com/watch?v=BDtrDv6uZTs&t=752s

Ah, got it now. Yeah, I'll be limited in length. But it's a sort of vague limit. I don't doubt that I could do something that is 8 or 9 inches long by having a template that extends out past the little platform. At some point things would become too flexible. But there's nothing I need to make that I can imagine that will be more than maybe 6 to 7 inches in length.

TECHNICALLY I could run a copy that is as long as I have travel for with the lathe minus the length of the offset between the cutter and stylus. So about 30 inches I guess. It would require a lash up support for the free end of the template though.

[JRouche]

I am better on the Lathe than the Mill..

And, I am only ok . JR

[BCRider]

Looking at this I see that I skipped over the hand turning bit and video. I did actually make a small part years ago using a graver style cutter. But HOOOO BOY! It is a SLOW process with gossamer like shavings as a limit unless you're willing to risk a dig in and flipping the tool out of the hand. Heck, watch your tool holders and tools on a lot of the lighter lathes during any sort of heavy roughing cut and it's not uncommon to see things flex just a little. We don't see it on the big lathes but if we put a dial gauge on the tool even on the heavy monsters I would be surprised if the cutters don't deflect by at least a little.

So no, I won't be opting to turn a 6 to 7 inch long ball end hand crank out of 1.25 stock any time soon with a hand graver....

[npalen]

You may have noticed that he did all the roughing of the shape with conventional lathe cutting but, yes, there is definitely some finesse involved in doing the hand work in final shaping. Looked to me like he was pulling some nice sized shavings with the gravers, however. I'm guessing that RPM (SFPM) and sharp tools are important for good cutting action.

Going back to the first video you posted, I wonder if there may be quite a difference in the profiling success with and without the ball bearing to guide the stylus. Going downhill on the bearing looks like you can apply a fair amount of force with the cross slide and let it do the work. Have you actually seen anyone profiling against a solid template as you're contemplating? I could see roughing out the shape fairly close with that method letting the template establish all the reference points for final profiling. That's basically how the woodturners do complex shapes.

[BCRider]

My assumption, which might be all that this implies , is that the ball bearing on the video is just a handy thing to use as a template. I don't think that the low rotation drag was part of the process. It might have helped a little but I don't think it was a main point of using it.

[Paul Alciatore]

I disagree. If the cutting tool has sharp corners then you want the follower to also have sharp corners so that the shape is the same. And sharp corners on the follower would dig into a stationary pattern, making it difficult to go up-hill at least. So I do see the use of a ball bearing as a useful, if not necessary part of the original idea.

My assumption, which might be all that this implies , is that the ball bearing on the video is just a handy thing to use as a template. I don't think that the low rotation drag was part of the process. It might have helped a little but I don't think it was a main point of using it.

[BCRider]

You're right Paul. But that assumes a sharp corner. I plan on at least a small matching nose radius to both cutter and follower stylus.

I'm also going to run the passes such that I'm never fighting against a screw. One option is start at a high point and applying inward pressure on the cross slide wheel and then traverse the carriage so I run downhill from the peak of a shape. Or if starting at the valley I might apply some carriage pressure into the shape and draw the stylus back out with the cross slide. But the idea is that I plan to always be running "downhill" or "following" a shape so the template does not need to fight against a lead screw thread at any time. And if I don't keep up then it "fails" into the waste area in either case and I just run another pass with more control of the movement.

[npalen]

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!

[npalen]

I disagree. If the cutting tool has sharp corners then you want the follower to also have sharp corners so that the shape is the same. And sharp corners on the follower would dig into a stationary pattern, making it difficult to go up-hill at least. So I do see the use of a ball bearing as a useful, if not necessary part of the original idea.

I tend to agree that going downhill on the template would appear to be easier than uphill but, the more I think about it, I wonder exactly why that is. What are the dynamics other than feeding the carriage with one hand while feeding the cross slide or compound with the other while trying to synchronize these motions? The cutting force would tend to overrun the cross slide leadscrew when going uphill but what is different going downhill?

[BCRider]

I've not done the tracing thing yet but I have done a few "free coordination turning" And it was always easier to pull back and try to follow the shape already there.