Metal spinning help

[Joe Hillmann]

I tried spinning a pair of half spheres out of aluminum yesterday and well it wasn't a total failure, it also wasn't a success. The form that I made was about 2 1/4 in diameter but the finished pieces of spun aluminum ended up having a "diameter" of closer to 5 inches. As I pressed in on the side close to me the opposite side pulled away from the mold and no matter what I did I couldn't get it to stay tight to the mold.

So basically I am wondering if anyone here knows how to spin sheet metal and if so if they could offer me any pointers.

[Jim Underwood]

There are a couple of metal spinning forums around... you might try asking on one of those.

I'm interested in any replies you might get here though. I've a passing interest in the subject. If anyone nearby does metal spinning, I'd love to pick your brain, and perhaps ask you to do a demo for our club.

[Dean Jordan]

That sounds like an unusual problem.A few questions. What speed are you using? What thickness of aluminum? and what grade of aluminum.
You shoulb be using pure grade aluminum about .040. gauge. your speed has to be faster with a small spinning. I don't know how you can get a 5 in diameter. tha disc you start with only needs to be 20 percent bigger than the finished diameter of your half spherehope this helps
Dean

[Joe Kaufman]

Penn State Industries has a free metal spinning DVD available.

Joe

[Joe Hillmann]

I think I am using 3003 aluminum, it is 22 gauge (.025) and rpm is around 1800, maybe higher but the motor bogs down a bit so not to sure on speed.

I just ordered the free DVD which has free shipping as well so hopefully when that gets here it will help.

[Dale Miner]

Hi Joe,

I do some metal spinning and also do demos.

In the 3003 grades, there are several tempers. You should be using 3003 - 0 which is dead soft. 3003-0 is not commonly available. 3003-H14 is more common, and that may be what you have. 3003-H14 can be annealed to the -0 temper state by heating to about 500 degrees and allowing to cool slowly or quenching in water. Do not use 5052 or 6061 in any temper grade while learning.

For starting out, .025" is a bit on the thin side, although it is doable for the size sphere you want to spin with proper technique. You would have better luck with .040" material.

1800 rpm is to fast for me for that size object. I would probably spin those at 800 to no more than 1000 rpm. I suggest you start out at about 400 to 600 rpm. You will need to lubricate the disc and use a steel spinning tool.

For a 2.5" half sphere, start out with a 3" disc. That may not be quite enough material to form the part, but it is better to start with a to small disc and adjust the size larger than the other way around. A disc that is to large will become thin and cause all sorts of troubles.

Spinning a sphere takes a bit of a combination of techniques. Start out by laying the material down on the form using a single forward stroke until you have about half of the diameter of the form covered. At that point, start to work the material into a 45 degree cone using mostly forward strokes with some light pressure on the back stroke. You may need to use a back stick to prevent buckles during this part and most of the next. Once the material is in a cone shape, begin laying the material onto the rest of the form in increments with a combination of forward and back strokes. Put about 1/4" of material on the form with each back stroke, and reduce the diameter of the cone with the forward strokes. Using forward strokes only will thin and tear the material. The material must be tight to the form as you proceed. If any area is left loose on the form, it will be nearly impossible to go back and lay it down. Usually, if a spot is left loose, attempts to lay it down result in a bulge at the follower block. When you have about 3/8" left to complete the half sphere, trim the edge true and lay the remaining material on the form using the larger radius or flat side of the tool.


Hemishperes are not the easiest part to learn to metal spinning on.

[Joe Hillmann]

Dale. What is the easiest shape to lean on?

I only did a half sphere because I figured it would be easy since there are no sharp turns on it. As far as the aluminum, I am using the bottoms of cake pans(I bring hundreds of them in for scrap metal every year so for now that is what I plan to practice with). Idealy I would like to work in copper but that is a bit pricey to learn with.

I think part of my problem was my live center wasn't pushing the disk into the form over a large enough area which cause the side opposite the operator to lift when I pushed the metal in on my side. Which since it worked at all for me and I did end up with a piece that had a rounded shape I am sure with a little bit of playing I can get it to work like I want.

[Dale Miner]

Dale. What is the easiest shape to lean on?

I only did a half sphere because I figured it would be easy since there are no sharp turns on it. As far as the aluminum, I am using the bottoms of cake pans(I bring hundreds of them in for scrap metal every year so for now that is what I plan to practice with). Idealy I would like to work in copper but that is a bit pricey to learn with.

I think part of my problem was my live center wasn't pushing the disk into the form over a large enough area which cause the side opposite the operator to lift when I pushed the metal in on my side. Which since it worked at all for me and I did end up with a piece that had a rounded shape I am sure with a little bit of playing I can get it to work like I want.

Joe,

In my estimation, the easiest shape is similar to the bell on a trumpet.