Newsgroups: rec.crafts.metalworking
Subject: Re: Spinning al tube on the lathe
From: jmorton@euler.Berkeley.EDU (John Morton)
Date: Wed, 3 Feb 1993 02:06:20 GMT

In article <wwebster-020293082335@47.220.4.56> wwebster@bnr.ca (Bill Webster) writes:
>A while back I posted a question about tuned pipes for
>engines.  Now that I've got some books on the topic,
>I'd like to make a tuned pipe.  The basic shape is like
>two ice cream cones with their large diameter ends joined
>end-to-end.
>
>To make such a shape, I believe I'll have to make the
>pipe in two pieces and aluminum weld them together.
>
>So, how do I get the basic cone shape, using a lathe,
>to spin a sheet of aluminum?
>
>I know (or think I know), that some sort of inside and
>outside follower is needed to help hold the shape.  The metal
>is worked slowly (what rpm? or feet per minute?).
>What do I use for a follower?  A piece of brass or tool steel??
 
You can find treatments of spinning in various books, if you
can't find anybody doing it, e.g. _Metal Techniques for
Craftsmen_, by Oppi Untrecht.
 
I have faked all the spinning I've done.  Here is a distillation
of the little I've learned:
 
	- Use soft aluminum.  This means type O.  You can bring
	alloys with the wrong temper down to the O state with
	heat treating recipes, found in metals reference books.
 
	- Use a lathe with lots of power.  The 3000 surface ft.
	per min. you would prefer may not be possible on a
	metal lathe, and a home wood lathe is not likely to
	have more than 1 hp. or so.  Possibly a lot of patience
	would subsitute for power, but it wouldn't be fun.
 
	- The more you get towards a cylinder in your shape,
	the more radical the operation becomes in terms of
	power requirements and what is demanded of the material.
 
	- The form (held in the headstock chuck) can be of
	any material.  You could laminate it from cutouts,
	then rasp and sand to shape.
 
	- Make tools from large maple dowels.  Fool around
	with shapes until you have something you like.
	Use grease or wax for lube.
 
	- A hard roller held in the lathe rest works OK (that's
	what the automatics use) but tends to groove the
	workpiece indelibly.  Better is to use wood tools and
	pry at the spinning part using a vertical pin as
	a fulcrum.  The pin will have to be moved to other
	positions as needed.
 
	- Needless to say, don't use a chuck which grips the
	form on the outside - you will come to grief when
	you tool slips and jabs into the spinning chuck jaws.
	Hold the form by a small center pin - the whole
	system (form, workpiece, tailstock block) will be
	held together by tailstock pressure.
 
	- You can harden your piece when you're done, if
	it's a hardenable alloy.  Check the book.
 
	- Wear safety glasses and stay out of line with
	spinning parts, insofar as possible.  Especially
	when you first fire it up.
 
	Lotsa luck!
 
John Morton					University of California
jmorton@euler.berkeley.edu			Mechanical Engineering
{decvax,cbosgd}!ucbvax!euler!jmorton		Machine Shop

Newsgroups: rec.crafts.metalworking
Subject: Re: More general info on Al spinning WANTED
From: jmorton@euler.Berkeley.EDU (John Morton)
Date: Wed, 3 Feb 1993 18:19:11 GMT

In article <15786.2b6ee8c3@ohstpy.mps.ohio-state.edu> edharris@ohstpy.mps.ohio-state.edu writes:
>	Could someone post informantion on spinning aluminum. Some practical
>tips would be great. Specifically, I would like to find out how hard it is to
>spin large (1-2 foot) Al hemispheres.
>
>	If this job is unrealistic for the amature, are there shops which will
>so this for a "reasonable" fee?
>
>Thanks
>Ed
 
I was hoping there would be an experienced spinner reading this group;
I have been having problems with a specific aspect of something I'm
trying to make.
 
However it's always blind leading the blind on Usenet, so I will
point the poster to my previous comments to the guy who wanted to make
aluminum cones.
 
With regard to this particular project, I would advise against
undertaking it, because it would be impractical without a large and
powerful lathe.  You would be starting with a disk of 20" to 40"
diameter.  It doesn't take much tool pressure to stall out a machine
with all that leverage.  I figure 10 hp. or more.
 
There are spinning outfits in all major industrial centers; at least
there are here.  They're in the phone book.  If you can specify
material, diameter and thickness, it should be easy for one to give
you an estimate.  If the size is not too important they will have
hemispherical forms from previous jobs.
 
John Morton					University of California
jmorton@euler.berkeley.edu			Mechanical Engineering
{decvax,cbosgd}!ucbvax!euler!jmorton		Machine Shop