Is it any different from copy turning? Just the choice of where to mount the template that is “different” But quite a good way to simply mount a small template and arrange the follower

Thankyou for that, Paul.

Well, yes, as Jason says it is copy turning with a different approach to the template, but certainly effective and worth knowing.

I’d ask:

Would using a button tool achieve a better finish? It won’t plunge cut very well so you’d probably need use a parting tool as shown to remove the bulk. It may also need a cylindrical follower of the same diameter as the button.

If the ball is to finish on a shank, such as for a control-rod end, would it be best to grind or oil-stone a tiny radius on the parting-tool to produce a root fillet?

Would using self-acting feed make life easier by giving you both hands to control the depth? If so it would be safest to use it in the receding direction, i.e. towards the chuck for that “side” of the ball, towards the tailstock for the outer “side”.

I was always taught if you must use a file in the lathe, use a slow speed and keep the file moving across the work. Holding it still can quickly produce blunt areas.

Noel –

It could do. An alternative may be a vertical pin that carries rollers of differing diameters, or a bar that carries pins of differing shank diameters above a constant grip diameter.

How elaborate you make the thing might rather depend on how many balls of different sizes you intend making. Or the method inspires you to make!

The independent balls at the end are intriguing. How does one complete them? The ball will almost certainly snap off as the shank reduces to near-nothing, especially at larger diameters (hence masses), leaving a pimple to be removed somehow.

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On presentation, I could have done with no “call-centre music” but instead a few words and some shots making the operation of the slides a bit clearer. Was the turner using purely manual feed or a combination of self-acting feed with manual depthing?

Clever. I wonder if you could make a sort of “inverting copy turner” by having the tool holder swivel freely. This could even enlarge/reduce size by varying the geometry…

One of those odd coincidences as I am giving a talk about a curvilinear slide at the St Albans club tonight.

On 10 December 2025 at 17:15 Nigel Graham 2 Said:

.. …It would have been interesting to see what that ball engages… ..

I know him well – they’re for hip replacements..

Very interesting, and what a simple idea.  Relatively inexpensive with the use of cheap bearings.  With a suitable follower, it may even work with plain templates rather than bearings.  I guess the required precision might dictate which.  Also, I think I’d be tempted to use a round nose tool and follower.  As Nigel suggests, the finishing technique will dictate the final use of the ball(s).

I see. No need to apologize for good habits, I just wondered if I had misunderstood something. Which I did at first, I got the image of a serrated guide plate for threads stuck in my head and I couldn’t figure out how that would work  🙂

I’m guessing the thingamajiggy is a self opening die head, we have something similar at work but I’ve never tried using it. It takes a fair amount of setup so it’s only needed for large series.

I’m not sure this will be of interest.

About 40 years ago I designed and made this attachment for machining prototype Fresnel mould tool inserts.

The inspiration for the design came from a radius dressing attachment which came with a large cylindrical grinder newly purchased by the company.

It works  by transferring the point of rotation into free air in front of the fixture, to cut the Fresnel prism angles the point of the tool is set on the centre of rotation,  this means the angle of the tool can be altered without its position moving in the Z or X axis, the attachment also  has a built-in sine bar at the rear for accuracy.

The majority of the lens made were based on a 1mm radial pitch, the centre portion  being simple Dioptric prisms ( every prism having a different angle and simple refraction) and at a point where the efficiency had decrease to a level the prisms changed to Catadioptrics ( light enters one face on the prism is refracted and then gets reflected off the other face of the prism and  exits the face of the lens) , each prism having two different angles.

All this to capture and control light from a bulb and turn it into a parallel beam.

To prove the concept worked the original tools were made from H S S steel but then tools were manufactured from natural  diamonds ( not any use for jewelry as they were brown!)

It really wasn’t possible to polish the machined surfaces because the accuracy would have been  lost. The diamond tools produced, combined with a air bearing and turbine driven spindle a surface finish that our Talysurf gave meaningless results.

To turn the prototype lens into production tool inserts, the lenses were Nickel plated for days until the desired thickness and then built up with copper plate to thickness of about 15 mm, the lens was removed and the plated copy was machined to fit the tool.

To cut a radius the tool would be positioned either forward of centre ,concave radius or rearward of centre to produce a convex radius.

Steve

On 11 December 2025 at 13:05 Steve P Said:

I’m not sure this will be of interest.

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Steve

It IS absolutely of interest!

Please do not even think about removing your post, in fact I for one, would appreciate knowing more about both the jig and the manufacturing process.

Thank you Steve

On 12 December 2025 at 09:32 Steve P Said:

I’d like to apologise for my previous post,  when I reread it, it SMELLS of showing off…..

Definitely not! Always interesting to see other work and ideas. If we all worried about showing off then nobody would post anything about anything.

Anyway I have a poor sense of smell!

Julie

Oh, Steve, by no means remove that!

It is a fascinating view into making something that would likely not occur to many of us, beyond knowing Fresnel Lenses are used at large scale for lighthouse optics (with separate glass prisms), and small scale for moulded-acrylic, wide-angle reversing-viewers on vehicles like motor-caravans.

@SteveP. Of course it’s showing off, that’s why we’re here. It’s allowed, especially when it’s that bad ass. Consider my mind thoroughly boggled. Even my flabbers are gasted.