[TheForge] metal spinning

[Jerry Frost]

Terry:

I wish I could explain what's happening in a competent 
manner. Father was a master spinner, one of the best on 
the west coast in his day but I was just shop help. I 
did what he told me, how he told me to do it. After a 
while I developed a feel for spinning and was able to 
start doig things without explicit directions but I 
wasn't at it long enough to really know what's going 
on.

When Dad's shop got to the point he had more than 4-5 
employees I came to the attention of OSHA and the 
insurance co. There was no way they were going to allow 
the 16 year old son of the owner work in the shop so I 
had to move on. I wasn't terribly heartbroken, I'd had 
a good taste of just how brutal the work was and didn't 
really want to make it my carreer.

Depending on how much power you can apply there are a 
few different ways to get to the same point. Spinning 
the stockpot on "How They Do It" is usually done in a 
CNC or powered lathe now days and the technique is 
called "shear spinning." This is where the blank (flat 
metal disk) is taken straight to the finished shape in 
one pass. This takes quite a bit of force but if you 
can deliver it it's the fastest and least stressful for 
the metal. Not all metals are suited to shear spinning 
of course.

The metal moves and stretches in a manner very similar 
to a pressed part when being shear spun. It thins in 
the same places and is upset in the sasme places. In 
the case of a shear spun cylinder like a stock pot 
there is no upsetting. You'll notice the outer diameter 
of the blank remains the same through out.

The same stock pot if spun with scissor tools would 
require many passes but if properly done would not 
require annealing. It too would be shear spun but not 
in a single pass. Stresses in the metal will be greater 
but the finished pot will also be much stronger, much 
like forging. The trick in this kind of movement is to 
keep the roler tool as close to the point where the 
blank breaks away from the die. This point is like the 
point where a brim connects to the hat. Passes out the 
blank will be necessary to keep it flat and moving the 
right direction.

 Virtually all production scissor spinning shops have 
been replaced by automatic and CNC spinning shops. 
There are a number of small hand spinning shops around 
the country and they can be found easily enough with a 
web search or a little finger walking in the yellow 
pages.

I really wish I could explain what's happening better 
but I only did it, I didn't really know what I was 
doing. I can still feel the metal under the tool, still 
hear it and smell the burning lube. I can still feel 
the tool in the sweet spot and feel/hear the part work 
hardening. I just can't describe it.

Wish I could, I'd write a book and give you a discount.

Frosty
-------------------------------
If it ain't forged
it ain't real.
Wrought iron is.
The FrostWorks

Meadow Lakes, AK.

From: "terry l. ridder" <terrylr at blauedonau.com>


> hello frosty;
>
> thank you for the reply. i seriously
> doubt that i would have the physical
> stamina for metal spinning. i would
> like to have a better understanding of
> what is happening to the metal, by
> what, and how. also to have contacts with
> metal spinners in case i would need to refer
> someone to one.
>
> it appears that the metal is being deformed
> , stretched in one location and compressed in
> another location. given the starting shape of
> a metal circular disk and the ending shape for
> example a simple right circular cylinder. a
> stock pot. there is some serious plastic
> deformation occurring but i am not understanding
> where and how. that is what i would like to
> understand.
>
> On Mon, 25 Feb 2008, Jerry Frost wrote:
>
>> Terry:
>>
>> If you want to make an analog using clay,
>> look to a potter's wheel. They not only
>> look like the same process is going on,
>> it is in large part the same process.
>>
>> As the tool is passing over the blank the
>> metal is usually stretching to conform,
>> however it can and must be upset as well
>> to prevent failures.
>>
>> Rotation speed is determined by a number
>> of variables: dia., material, thickness,
>> shape of the finished part, type of tooling,
>> (specifically, hand > vs. scissor tools)
>> personal preference and skill among other
>> lesser factors.
>>
>> Annealing may or may not be necessary depending
>> on many of the same factors that determine
>> rotation speed. Pure Al is generally easily
>> spun without annealing as long as the shape
>> isn't too extreme and the spinner's skill level is 
>> decent. Most people are taught using
>> Al as it's so easily spun. On the other hand
>> the wrong type of Al can be a real PITA to spin,
>> most of the AL we spun in Father's shop was far
>> FAR from easy to spin. I thought SS was easier
>> and most spinners look on SS with fear and dread.
>>
>> My personal favorite is mild steel, it likes to
>> go fast, (high rpm) responds well to a sensitive
>> touch and almost never fails catastrophically. (read 
>> flying shrapnel) Brass is a PITA usually requiring
>> multiple heat treats unless you're spinning a very
>> simple shape or one you can really hog.
>>
>> Copper is like spinning taffy, requires little
>> force and spins really well but work hardens
>> suddenly so you have to be on your toes and
>> have a good feel for it. Still, copper is good
>> teaching material.
>>
>> I don't know of any good books that cover the
>> kind of spinning we did in Father's shop; we
>> were a production shop and used almost exclusively
>> scissor tools. Most people spinning manually now
>> use hand tools and I'm unfamiliar with the 
>> technique.
>> I'll have to ask a couple of my old contacts and
>> then get back with the name of decent books.
>>
>> However, on the practical side. Are you thinking
>> of trying metal spinning Terry? If so you're not
>> going to meet with much if any success, it's VERY 
>> phisical and if you let it get away from you
>> extremely dangerous. Think about a 6-9" diameter
>> metal blank spinning maybe 3,000 rpm. coming out
>> of the lathe and ripping it's way up your arm. A
>> part can also explode if pushed too far or hard
>> and the shrapnel can be almost impossible to avoid.
>>
>> I've personally practiced 1st. aid on the aftermath.
>> On one occasion it took three of us to apply 
>> pressure
>> to enough places to control the bleeding. Though 
>> nobody died in Father's shop a number of guys
>> lost fingers, the use there of and in one extreme
>> case his entire hand. Dad's insurance paid for LOTS
>> of stitches.
>>
>> Metal spinning can be very challenging, intensely
>> satisfying, hypnotically beautiful to watch and
>> cripplingly dangerous. It also takes a number of 
>> specialty or specially modified machines.
>>
>> Frosty
>>
>
> -- 
> terry l. ridder ><>
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