metal spinning mirrors
 

Hi all,

I'm having a problem spinning some mirrors for some experiments. The mirrors
are parabolic in shape, and I will place a light globe in the centre. The
trick is for my report I need to compare different curvatures, eg, deep
parabolic bowls and shallow bowls.

I have a Record woodlathe which I have been using in an 'outboard'
arrangement. The bowls themselves are 12 inches in diameter. I turned the
mandrels from hardwood that I laminated in a criss-cross fashion like
plywood mounted using a faceplate. To spin the metal bowls I have been using
0.3mm Aluminium from the local hardware shop. I'm not sure of its hardness
so I annealed it by baking it in the oven at the highest setting and turned
off the oven and let it cool slowly as the oven cooled down.

Maybe this was my first mistake but I have noticed in other threads that
some recommend quenching the metal in water etc after heating. I would of
thought this would have hardened it but maybe I am mistaken.

The aluminium disks are attached to the mandrel by a centerbolt at the back
of the faceplate which protrudes through the mandrel and the aluminium. A
2'' washer and nut are then used to tighten the aluminium against the
mandrel.

I have turned 3 shallow mirrors so far with fair results, however now that I
am starting to spin the deeper bowls I am finding the aluminium is cupping
back towards me (I stand end on off the lathe so the job wont slice me in
half incase everything breaks down). Cupping did occur with the shallower
bowls but I was able to apply enough pressure to correct it and finish the
job. Now however if I apply too much pressure I notice small creases in the
aluminium when I stop the job midway.

I would like some advice firstly regarding the metal. I find even though I
*thought* I softened the aluminium that it is quite stiff nonetheless and am
wondering if it is pure aluminium. I am hoping someone could offer some
advice on the type of metal I could use for best results, particularly the
thickness. I am wondering if I went a bit thicker whether the job would
spring back at me as I apply pressure. Also I was considering whether
something other than aluminium might be the go.. maybe copper? I dont have
alot of experience at the metal stuff. I am using a spoon shaped tool, I
whittled and sanded out of some eucalypt. I have been using a liquid wax
polish for lubricant whilst the job is underway.

Thanks in advance

Nick

On Tue, 2 Aug 2005 22:22:22 +1000, "Nick" wrote:

Nick,

so I annealed it by baking it in the oven at the highest setting and turned
off the oven and let it cool slowly as the oven cooled down.

Maybe this was my first mistake but I have noticed in other threads that
some recommend quenching the metal in water etc after heating. I would of
thought this would have hardened it but maybe I am mistaken.

I'm not a metallurgist, so I can't say definitively if different
metals react in different ways, however, I can tell you that when
metals like silver and brass get work-hardened, you anneal them by
heating them cherry red and quenching them in water. This I have
learned from reloading rifle and pistol cartridges (the case mouth can
get work hardened from repeated loading and crimping) and from doing
some amateur silversmithing. Both processes (handloading and
hammering silver) definitely benefitted from this annealing procedure.


--
Chuck *#:^)
chaz3913(AT)yahoo(DOT)com
Anti-spam sig: please remove "NO SPAM" from e-mail address to reply.


September 11, 2001 - Never Forget

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Hi Nick

Normally metal spinning is done between headstock and tailstock, the way
you are doing it is very dangerous imo.

Only deadsoft alluminium and pewter are not work hardened, gold silver
copper brass and alluminium are work hardened.
you need good lubrication while spinning or you get the galling that you
got.

I think that you should use pewter for what you are trying to do, it's a
lot easier to work with, copper also works well and is less costly and
can be annealed easily.

The book: "Turn a bowl with Ernie Conover" has a couple of pages devoted
to metal spinning.

Here are a couple of links to metal and metal spinning sites, you should
be able to get some more info there.


http://users.moscow.com/oiseming/lc_ant_p/lnk_mtal.htm

http://www.paulwileyspinning.com/

Have fun and take care
Leo Van Der Loo

Nick wrote:
Hi all,

I'm having a problem spinning some mirrors for some experiments. The mirrors
are parabolic in shape, and I will place a light globe in the centre. The
trick is for my report I need to compare different curvatures, eg, deep
parabolic bowls and shallow bowls.

Thanks in advance

Nick

"Nick" wrote in message
...
Hi all,

SNIP......
I would like some advice firstly regarding the metal. I find even though I
*thought* I softened the aluminium that it is quite stiff nonetheless and
am wondering if it is pure aluminium. I am hoping someone could offer some
advice on the type of metal I could use for best results, particularly the
thickness. I am wondering if I went a bit thicker whether the job would
spring back at me as I apply pressure. Also I was considering whether
something other than aluminium might be the go.. maybe copper? I dont
have alot of experience at the metal stuff. I am using a spoon shaped
tool, I whittled and sanded out of some eucalypt. I have been using a
liquid wax polish for lubricant whilst the job is underway.

Thanks in advance

Nick
=============
If you're looking for "near pure" Aluminum, try to find some 1100. We used
that for calculating penetrating power of diagnostic X-ray systems. It's
over 99% pure Al. (Seems that I remember it having trace amounts of copper.)
I think copper would be a better metal than Al, since it tends to be more
malleable, and I think that's what you want in spinning.

Ken Moon
Webberville, TX.

"Leo Van Der Loo" wrote in message
...

Hi Nick

Normally metal spinning is done between headstock and tailstock, the way
you are doing it is very dangerous imo.

Only deadsoft alluminium and pewter are not work hardened, gold silver
copper brass and alluminium are work hardened.
you need good lubrication while spinning or you get the galling that you
got.

I think that you should use pewter for what you are trying to do, it's a
lot easier to work with, copper also works well and is less costly and can
be annealed easily.


Copper is a good choice. "ductility" is what counts. Then electroplate for
your mirror experiment. easy enough.

http://en.wikipedia.org/wiki/Ductility

1. The aluminum in hardware stores is probably 1100 (99% pure aluminum.)

2. It was probably in the annealed temper.

3. Regardless, you followed an appropriate practice to anneal it. If you
got it red hot, it would have melted. Quenching in water is not required.

4. Because you got fair results with shallow bowls. I conclude that you
should do an intermediate anneal after partially spinning the deep bowls.
Hold for 2 hours at the highest temperature that your oven will attain.

5. I have never spun metal on a wood lathe. Here's what Dave Hout did on
the Woodturning show on DIY network to spin aluminum:
a) made a male form and attached to the headstock.
b) made a small "tail block" and attached to tailstock.
c) centered an aluminum disc between the two.
d) used a vegetable oil lubricant.
e) buffed to a shine.

6. I recorded the show. I will E-mail a copy to you, if you like.

7. You may wish to try aluminum closer to 1 mm rather than 0.3
mm. The appeared to be about the thickness that Dave Hout used, but I
couldn't really tell.

p.s.
I have been an aluminum metallurgist for 40 years.


"Nick" wrote in message
...
Hi all,

I'm having a problem spinning some mirrors for some experiments. The
mirrors are parabolic in shape, and I will place a light globe in the
centre. The trick is for my report I need to compare different curvatures,
eg, deep parabolic bowls and shallow bowls.

I have a Record woodlathe which I have been using in an 'outboard'
arrangement. The bowls themselves are 12 inches in diameter. I turned the
mandrels from hardwood that I laminated in a criss-cross fashion like
plywood mounted using a faceplate. To spin the metal bowls I have been
using 0.3mm Aluminium from the local hardware shop. I'm not sure of its
hardness so I annealed it by baking it in the oven at the highest setting
and turned off the oven and let it cool slowly as the oven cooled down.

Maybe this was my first mistake but I have noticed in other threads that
some recommend quenching the metal in water etc after heating. I would of
thought this would have hardened it but maybe I am mistaken.

The aluminium disks are attached to the mandrel by a centerbolt at the
back of the faceplate which protrudes through the mandrel and the
aluminium. A 2'' washer and nut are then used to tighten the aluminium
against the mandrel.

I have turned 3 shallow mirrors so far with fair results, however now that
I am starting to spin the deeper bowls I am finding the aluminium is
cupping back towards me (I stand end on off the lathe so the job wont
slice me in half incase everything breaks down). Cupping did occur with
the shallower bowls but I was able to apply enough pressure to correct it
and finish the job. Now however if I apply too much pressure I notice
small creases in the aluminium when I stop the job midway.

I would like some advice firstly regarding the metal. I find even though I
*thought* I softened the aluminium that it is quite stiff nonetheless and
am wondering if it is pure aluminium. I am hoping someone could offer some
advice on the type of metal I could use for best results, particularly the
thickness. I am wondering if I went a bit thicker whether the job would
spring back at me as I apply pressure. Also I was considering whether
something other than aluminium might be the go.. maybe copper? I dont
have alot of experience at the metal stuff. I am using a spoon shaped
tool, I whittled and sanded out of some eucalypt. I have been using a
liquid wax polish for lubricant whilst the job is underway.

Thanks in advance

Nick

Ken has it right.
I turn wood, plasma cut metal and turn and mill metals.
In my Metals Handbook - phone book size and about a USD$ per page (ugh!)

1100 is "Commercially pure aluminum highly resistant to chemical attack and weathering.
Low cost ductile for deep drawing and easy to weld....... fan blades, flue lining, sheet
metal work - SPUN HOLLOWARE - and fin stock.

Good luck.

Martin

Ken Moon wrote:

"Nick" wrote in message
...

Hi all,


SNIP......

I would like some advice firstly regarding the metal. I find even though I
*thought* I softened the aluminium that it is quite stiff nonetheless and
am wondering if it is pure aluminium. I am hoping someone could offer some
advice on the type of metal I could use for best results, particularly the
thickness. I am wondering if I went a bit thicker whether the job would
spring back at me as I apply pressure. Also I was considering whether
something other than aluminium might be the go.. maybe copper? I dont
have alot of experience at the metal stuff. I am using a spoon shaped
tool, I whittled and sanded out of some eucalypt. I have been using a
liquid wax polish for lubricant whilst the job is underway.

Thanks in advance

Nick

=============
If you're looking for "near pure" Aluminum, try to find some 1100. We used
that for calculating penetrating power of diagnostic X-ray systems. It's
over 99% pure Al. (Seems that I remember it having trace amounts of copper.)
I think copper would be a better metal than Al, since it tends to be more
malleable, and I think that's what you want in spinning.

Ken Moon
Webberville, TX.




--
Martin Eastburn
@ home at Lion's Lair with our computer lionslair at consolidated dot net
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder

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Leo Van Der Loo wrote:
Hi Nick

Normally metal spinning is done between headstock and tailstock, the way
you are doing it is very dangerous imo.


I try to be safe.. I use overalls, gloves and a full face mask and I
never move past the spinning disk in case it spins off. I figured that
if I secured the disk to the mandrel securely (big enough washer and
bolt) everything should be ok. Touch wood, I've never had anything
weird happen yet.

Nick

Thanks for that info Jim, and everyone else who's replied. I had a good
baking today of a disk for a couple of hours and it seems to have
worked. I've got 80% through the job before I've stopped it and I'm
baking it again. It seems that you are right. I just need to anneal it
a few times to get the job finished.

I called the shop where I bought the aluminium today and they didnt
have any info on the type of aluminium so I must assume its as some of
you said 1100. I also rang a metal supplier I've used in the past for
bit of copper on occassion and the sales lady actually asked if its for
spinning which I was happy about. It seems that there is a local
spinning business nearby which uses either 5005 or 1100 aluminium. A 3
foot by 6 foot sheet of 1mm 5005 runs in at $58 so I might need to pick
some of that up as I'm not going to have enough of the other, and then
I'll be able to do some comparison of the two.

The only other thing I did today was to increase the washer used to
affix the aluminium dish to the mandrel. Its an unusual way to spin it
I guess but without a very large swing on a lathe its a bit hard to use
a tailstock. At least my ghoulies are firming up a bit!

I'll keep the group posted about the results.

It'd be great if you could email me that video of what dave hout did
Jim. My email is

Thanks very much
Nick

Nick wrote:

something other than aluminium might be the go.. maybe copper? I dont have
alot of experience at the metal stuff. I am using a spoon shaped tool, I
whittled and sanded out of some eucalypt. I have been using a liquid wax
polish for lubricant whilst the job is underway.

I wonder if using a steel tool would be more efficient, and allow
forming your shape fast enough so you wouldn't need to anneal more than
once. Use the same spoon shape or a full-round bullet shape, highly
polished, with wax lubricant.
Give it a long handle, so you can use your body to manipulate the tool
and apply more pressure. You might need a secondary tool on the inside
to help keep the unspun metal from buckling.
My wood lathe in it's former life was a dedicated metal spinning
machine. It came with a toolrest consisting of a 1" square by 10" long
steel block, with several holes on the topside for leverage pins.

Ken Grunke
http://www.token.crwoodturner.com/shop/

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