Thread: video---Russian method of sphere cutting

How to make perfect sphere on a lathe - YouTube

This method is described at length in Tom Lipton's book "Metal Working - Sink or Swim". He uses a boring head and rotary table on a mill.

A few years ago i posted about PM member Alwyn's "seminar" on various means to use the same technique. He graciously toured us through his plant in Denbighshire and demonstrated a number of machines and procedures. Unfortunately, the Metalworking Dropbox moved, and the picture links are broken in the original.

Same principle as the video, but perhaps a bit more finesse. In this case, bigger parts for more critical applications. Male and female laps, or sometimes "chucks" for, IIRC, glass industry. (IIUC, when used as a chuck, multiple lenses are adhered for further machining or lapping operations, rather than the shape itself being the lap) As Alwyn observed, "making them is not that difficult; but measuring them is..." (OWTTE) whenever the shape is less than an actual half sphere. Given the application, the tolerance for Alwyn's work is close.

There are machines designed for the purpose of turning spherical shapes, here is one in Alwyn's plant. It is apparently not much used, preference being for a shop made set up on the BP mill (later)



demonstrating the machine above:



Another "factory" machine to do the same job, this one in the boneyard at Alwyn's. I think Mark (aboardepsilon) was angling for it at the time, have not heard an update?



Rotab on BP, with shop devised belt driven power from a windshield wiper motor. Originally supposed to be "temporary" but just keeps on running.



ID spherical shape



OD shape



smt

Why cant more people just simply turn it free hand?

Originally Posted by JHOLLAND1

How to make perfect sphere on a lathe - YouTube

Huh? What I'm seeing made is a semi-sphere, not a sphere.

Sphere - Wikipedia, the free encyclopedia

Gordon

interesting lathe. it seems that an overhead bed makes sense, cuts wear down, nothing drops on it, if carriage was on it then controls would be easier to see. hmm.

Originally Posted by Gordon B. Clarke

Huh? What I'm seeing made is a semi-sphere, not a sphere.

Gordon

Thanx a ton for pointing that out, Gordon.


Rex

Originally Posted by oldbikerdude37

Why cant more people just simply turn it free hand?

Good point OBD, but in Alwyns case I think his parts have to be to a tightly specified radius,...... optics rings a bell.

Lots of people ignorant but capable people have independently discoved that a radius revolved around one axis describes a spherical solid on an intersecting axis. This abstraction applied in a machine shop by a variety of machine tools and techniques produces accurately generated spheres.

A Russian may have made the video but the "method" if there is one has been around since Euclid and probably before.

BTW, if that fellow's die grinder axis is above or below the spindle axis his "sphere" becomes football shaped.

As Forrest (and others) said, that method is well known for generating spherical shapes.

The interesting thing to me in the video was the cutter design. The cutter head appears to have a counterweight welded or brazed on to the opposite side of where the carbide cutter is brazed. I think the counterweight is important for the life of the cutter, life of the die grinder bearings and finish of the spherical ends on those bolts. He omits the counterweight in the animation.

The video itself is a pretty good production when compared to many machining videos on youtube. They maximized the information to get the idea across while the minimizing the length of the video. Only thing I would have dome differently is to have a flip down work shield (possibly omitted for clarity)... if and when that cutter breaks loose safety glasses won't be enough.

-DU-

Originally Posted by bjorn toulouse

Thanx a ton for pointing that out, Gordon.

Rex

Was that a genuine thank you or a sneer? Why the rolling eyes?

Gordon

I imagine that this method originally derived from the simple, hand manipulated, hollow tube cutter used to cut solid balls from ivory, wood and similar materials. The geometry involved is rather more subtle than it seems when considering how the basic tube cutter is manipulated to create balls whose diameter is equal to the tube bore.

Its quite easy to end up with a surface geometry considerably variant from a true spherical curve. Especially with small components on a stalk, as shown in the video, where the actual cutting point on the tool tends to wander along the edge as the cut deepens. Ideally you need a perfect point cutter but this is impractical for all sorts of reasons. Clearly the larger the spherical radius the closer a practical cutter approximates the ideal point and the easier it is to get a true spherical form. Initial set-up needs to be precise too.

The optical workshop at my former employers had a small Adcock Shipley vertical mill (1 ES?) fitted out for producing one-off lens grinding tooling by this method. I have the impression that it was a production item, not a one off or locally modified. Significant calculation was needed to get the set-up right for optical standards of accuracy. Especially if an aspheric shape were required. Over the years I got tasked with updating the original hand written table of settings into the modern computer age. Firstly via programmable calculator, then BBC "B" micro and finally Excel spreadsheet. I've probably still got an HP67 magnetic strip with that version, or more likely the remains of that version, on it. The optical designers were unimpressed when I suggested that tooling design should be part of their remit as the PDP11, Vax, MicroVax or whatever they were using at the time would be a lot quicker than a BBC!

Clive

Originally Posted by Gordon B. Clarke

Was that a genuine thank you or a sneer? Why the rolling eyes?

Gordon

Sarcasm - Wikipedia, the free encyclopedia


Rex

I was interested in the - what appeared to be -an HSS bit silver soldered to a mild steel bar. I have silver soldered many carbide tips to a steel shank but never an HSS one. How do they last, does the heat cause any problems?
Clive

Originally Posted by Clive Hugh

I was interested in the - what appeared to be -an HSS bit silver soldered to a mild steel bar. I have silver soldered many carbide tips to a steel shank but never an HSS one. How do they last, does the heat cause any problems?
Clive

Very well do it all the time a lot of my work needs specials- use Easyflow 2 and the right flux, and use just enough heat to get the silsol to flow.

Sami,
We used Easyflow when I lived in New Zealand but in Australia it's sold by the silver content not brand name, the closest I find is 46% silver. I was wondering about the heat treating side of it. I assumed, rightly or wrongly, that HSS was treated in some way, either oven or hot oil quenching and that brazing would ruin any treatment
Clive

HSS will take the temperature of the lower temp silver solders with no harm. Don't quench it to avoid cracking. Easyflow No2 is about the lowest melting point silver solder. Better if it's old enough to have some cadmium in it

Originally Posted by bjorn toulouse

Sarcasm - Wikipedia, the free encyclopedia

Rex

As my dad often said, "Sarcasm is a form of humour in which only fools indulge".

If it's any consolation then it was said when I myself was sarcastic

Gordon

I've finished some 16" bronze castings on a BP using this method. Head on 45deg, motorized rotary table and a big honkin fly cutter with 2 toolbits, north pole and equator. Worked a treat!
To me, far more intersting is using a fly tool to generate a finely finished _parabolic_ surface[for focusing lasers??]. JinNJ