Subject: Re: sphere turning jigs?

From: [email-masked] (Mark Kinsler )
Date: Fri, 26 Jan 1996 06:26:37 GMT

In article <alberic.822551229@access4>,
Brian Meek <[email-masked]> wrote:
>Greetings all:
>I have a question, actually, I have many, but I'll keep it down to one 
>tonight.  I've been needing to turn some sphere headed punches for 
>forming sheet metal.  I have a pair of lathes, and should be able to do 
>this with one of them, but I can't think up the proper jig.
>(Lathe #1 is an Ames 6" collett lathe, (grandad to the Hardinge)
>and #2 is a SB 9" heavy.  (Has the same bed/apron as the 10")
>There's no real urgency to this, but it'd be nice eventually.
>I seem to remember that there's some sort of attachment that can ride on 
>the compound rest of an engine lathe, but I can't remember what it looks 
>like, or where to get one.  

Popular Science Monthly had an article on how to build a ball-turning
attachment.  It attached to the toolpost, I believe.  The article ran many
years ago, probably in the 1960's, and I imagine that the author was Harry
Walton.  Popular Science is well indexed, so it shouldn't take too long to
find the issue in question at the library.  Check the Reader's Guide to
Periodical Literature as well. 

                                      Mark Kinsler

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From: [email-masked] (MBStudios)
Date: 26 Jan 1996 04:44:20 -0500

I've seen some one clamp a rotory table onto the saddle, and with the tool
post mounted on the table. Though turning full spheres I would think would
be beyond this set up.

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From: [email-masked] (Russ Kepler)
Date: Sat, 27 Jan 1996 04:55:53 GMT

>There's no real urgency to this, but it'd be nice eventually.

Metal Lathe Accessories sells a set of castings for the SB 9" that
make into a ball turning tool and a boring bar toolpost.  I've made
the set for my Atlas 12", and found the castings nicely done, with
good drawings and instructions.  Fun to whack out some cast iron, and
this is the third or fourth MLA castings I've used, always with good
luck.

What you want is the MLA-13, price about $50 with the neat-o cast iron
handle.  Shipping can be difficult with big castings.

 Metal Lathe Accessories 
 Box 88
 Pine Grove Mills, PA  16868

 814-234-3543

 Talk to Andy Lofquist

There are more accurate ball turning attachments - this is not
terribly accurate (in the sense that if you want a 1.000" +- .001"
this is not the tool you want.  If you're more in the range of +-
.005" this can work but it's more for +-.010, at least in my casual
use.

-- 
Russ Kepler posting from home  [email-masked]

                      Please don't feed the Engineers

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From: [email-masked](Dale A. Keltie )
Date: 25 Jan 1996 23:34:58 GMT

In <[email-masked]> [email-masked] writes: 
>
> <Keltie's babbling snipped>
>
>I've seen them listed (and pictured) elsewhere recently---MSC catalog?
>Rutland Tool catalog?--but if the piece isn't too big and you don't
>care if it deviates from a true sphere by several thousandths, you
>could always turn a step approximation to a sphere, using a calculator
>to tell you what cuts to take, and smooth the ridges afterward. This
>stops being much fun after an hour or two, though, I've found.
>
>                      ...when I sit down to write
>Don Holly             my intentions are always blameless however
deplorable
>                      the ultimate effect of the act may turn out to
be.
>                                           --Joseph Conrad

Mr. Holly's suggestion brings to mind yet another method, commonly
used in machining molds and forming dies; contour milling.  The folks
who do this regularly use CNC milling machines, and sophisticated
computer software to generate the appropriate tool paths, to cut any
surface they need but you can cut a spherical surface with a manual
vertical mill and a rotary table.  Note that you have want that surface
pretty badly,  this technique is even more tedious than that Mr. Holly
suggests.

Using a ball end mill, cut successive circles of decreasing diameter,
at appropriate heights.  Leaving Y at the centerline of the rotary
table, incrementally move X toward the center of same, taking a cut
around the circumference of the spherical surface at each X increment. 
The equation for Z is:  Z = (R^2 - X^2)^.5; where R = the radius of the
sphere + the radius of the ball end cutter, and X = distance from the
center of the sphere.  The smaller you make the X increments, the
smaller will be the ridges around the sphere (and the more times you
have to crank the rotary table through 360 degrees.  By making the X
increments small enough, the ridges will be virtually impercepible and
you will be eligible for social security when you're finished (If our
pal Newt leaves any in the pot that is).

A company here in Reno, who fabricate structures of composite
materials, made a 40" dia. parabolic layup form of polyurethane foam
using this method.  They used a variable speed electric drill to run
the rotary table and it still took them DAYS to get it done.  
Afterwards, their customer changed the spec. slightly so they had to do
it again.  The customer was a major DoD contractor, they'll get it
right no matter how much it costs (us).

Regards, Dale

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From: [email-masked] (Lughaid)
Date: 27 Jan 1996 07:43:19 -0500

In article <alberic.822551229@access4>, [email-masked] (Brian
Meek) writes:

>like, or where to get one.  I have a 1920's vintage book on lathe jigs 
>that shows one way to do it, but it requires extensive hardware 
>modification to the lathe apron.  (Extra drive gears & shafting.)
>I'd really rather not start drilling big holes in my lathe if I can avoid
it.
>(not to mention adding extra gears and whatnot.)
>
>

Guy Lautard, author of "The Machinist's Bedside Reader," et al, has a
small book out called "Tables and Instructions for Ball and Radius
Generation."  It shows  how to do what he calls the incremental cut
method. 

John Dean, in an article entitled "Fear Neither Sphere Nor Hemisphere,"
>from  the early Home Shop Machinist Magazine, reprinted in "Projects Two",
shows how to make an offset plate, to mount on the slide, allowing the
compound center to rotate around a radius. The center of rotation, the
pivot point of the plate, is under the center of the ball you are to turn,
with the carriage, then it is locked. The compound, and cutter, set at
center height, are mounted on the plate, and are swung around the ball.
Adjustments of the cutter are done with the compound.

Hope this helps.
Michael Horgan, [email-masked], [email-masked]

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From: Bob Unitt <[email-masked]>
Date: Sun, 28 Jan 1996 14:10:33 +0000

In article <[email-masked]>, Rrice2 <[email-masked]>
writes
<SNIP>
>there is interest, I will try to draw one up and post to Metal Web News.
                                                          ^^^^^^^^^^^^^^
I seem to have missed that - what's the URL, please ?

-- 
Bob Unitt

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From: [email-masked] (Rrice2)
Date: 27 Jan 1996 05:55:54 -0500

In one of Guy Lautard's Machinists Bedside Readers, he gives a method of
ball turning by incremental cuts on the lathe. He also wrote it up in a
Home Shop Machinist article a few yeras back. I have tried it, and it
works just fine. A radius turning fixture is fairly easy to make, too. If
there is interest, I will try to draw one up and post to Metal Web News.

---

From: [email-masked] (Mick Collins)
Date: Sat, 27 Jan 1996 16:52:25 GMT

Brian does't mention the diameter of his punches but for sizes up to
an inch, either of those two lathes should be able to cope with a form
tool.  Soften an old file and bore to required diameter, setting top slide
to 5 degs to turn clearance on what will become the front of the tool.
   A round nosed tool will give something approximating to a rake angle
on the 'top' surface.   Saw and file to shape before hardening and 
tempering to light straw.  Use upside down from the back and set to exact
centre height.  Run at lowest speed.
   It worked fine for 9 off 3/4" ball handles for my Quorn. 

  -- 
     Cheers

  Mick  S.M.E.E.           "From the inventors shop came
                                 the sound of hammering tin"
  [email-masked]

---

From: [email-masked] (Antonio Palama')
Date: 29 Jan 1996 12:18:55 GMT

Brian Meek ([email-masked]) wrote:
: Greetings all:
: I have a question, actually, I have many, but I'll keep it down to one 
: tonight.  I've been needing to turn some sphere headed punches for 
: forming sheet metal.  I have a pair of lathes, and should be able to do 
The hemisphere turning procedure as described in the Holtzapffel book on plain
or simple turning involves the following steps:
1) Set the slide to run along the lathe axis and turn a cylinder whose
   diameter is the same of the sphere.
2) Set the slide at 45 degrees and cut a cone the depth of cut of the cone
   is decided by the requirement that the diameter of the remaining face
   of the work be equal to the lenght of the conical cut.
3) Set the slide at 22.5 and 67.5 degrees and cut two other conical surfaces.
4) Repeat with 11.25 33.75 56.25 78.75 degrees, and so on.

   The idea underlying this procedure is to produce a solid whose section
along the lathe axis is a square, an octagon, a 16-sided polygon, a 32 one
etc. so as to approximate a circle and hence a sphere.
   I use to finish up the work with a hand held file.
   Hotzappfel also gives a procedure to turn an exact sphere (ivory
billiard balls) by hand without the help of a slide rest but this requires
special holding jigs.
   Hope this helps.
Ciao, Antonio.