[TheForge] spinning with tool instead of mandrel?

[ries]

I think if this would work, somebody would have done it by now. 
The problem is rigidity- if your backing roller isnt stiff enough, the form that is spun will not be accurate or symmetrical.
And any moving arm is going to be much less rigid than a full form.
Maybe your idea would work for very thin, soft aluminum- but I cant imagine it resisting the forces of 1/8" stainless sheet, for example.
On heavier spinning forms, there is an amazing amount of force involved.
Some spinning patterns are made from aluminum, some from hardwoods.

CNC spinning lathes are very big and massive. A big one, capable of spinning 4' or 6' diameter parts, can easily weigh 20,000lbs or more- and the pattern might weigh in at 500 to 1000lbs. I just dont think you could get a strong enough cantilever arm in the space provided.

There are some CNC forming machines that use variable hit dome punches to form sheet metal- they look kind of like a big CNC turret punch, and instead of punching all the way thru, they merely emboss the metal. 

And then, there are people using spinning domes on a CNC milling machine to form sheet- good video on youtube of an experiment like that.
http://www.youtube.com/watch?v=GxysBla3NyI

ries


On Dec 26, 2010, at 11:20 AM, Bruce Freeman wrote:

An idea just popped into my head, and I wonder whether it's feasible.

Normally, metal spinning is done against a wooden form.  But hos necessary
is that?

Imagine a metal lathe with a rolling wheel mounted on a cantilevered rod to
the cross slide.  This wheel sits at the center-line of the lathe,
vertically, and is on the chuck side of the cross slide.  The cantilever
should be kept to a minimum so the device is very rigid.  This replaces the
wooden form.  (The wheel may be flat or radiused or otherwise shaped,
depending upon the work to be done.)

Now affix your metal disk (here presumed to have a center hole) to the
chuck, and start spinning.  The tool could be constrained to work only at
the vertical centerline of the lathe to keep the forces located
appropriately.

Anyone heard of any setup like this?

The advantage I'm thinking is the possibility of completely flexible, or
even CNC-controlled, metal spinning.

-- 
Bruce
NJ
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Ries Niemi
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