Slideman1939 - Posted - 03/10/2009:  14:30:55

I am interested in trial spinning, but I don't know where to get the blanks, in what thickness, and in what diameter.What is the thickness of a "standard" cone like Quarterman . What diameter does one puchase for a 10 & 1/2 in. Dobro style cone.Does a 10 & 1/2 inch cone start out as 11 &1/2 or 12 inch diameter because of the extra metal pushed down into the "sailor's hat" ???My questions are not on technique, but WHAT product specification one orders from the metal supply house.

prewar37 - Posted - 03/10/2009:  16:10:15

Slideman,
The aluminum use to spin shapes like bowls and such is very soft so it can be formed without tearing. I can't measure the thickness of my Q-cone cause it's in the dobro, but I have a 30's lug cone that is .012" thick. The rough size of the lug cone before it was stamped is roughly 12.625". They are spun or stamped with excess material around the edges and then trimmed to the final dia. or stamped in a die to a specific diameter. So the flat stock may have started out at 14" or so. Depending on the tooling available. The material could be a 6061 T0 aluminum alloy. It is very soft and workable but hardens a bit during the forming or shaping process. Its' called work hardening. Spinning a shape by hand takes time to master. You may be able to get some specifics from Beard or Gibson. If they can tell you without giving away any trade secrets.
Sounds like a challenging project. Good luck with it.
Keep on pickin' prewar37

Slideman1939 - Posted - 03/10/2009:  18:45:56

Thanks-that's exactly the diameter/thickness info I needed. You are correct that alloy# 6061 is the one to get. Sharing with you, previous research: there is a website called tweedsblues.net. Within that site, find the sublink "cone from Molonator guitar".It pictures a homemade dedicated spinning lathe and 5 photos of the owner spinning a cone. Molonator (Pete Moles) is an australian dobro luthier. Another site is metalspinningworkshop.com. This is a person in the Phila. area who spins & has a metal spinning school (classes) AND has for sale 3 DVD films picturing him at the lathe and explaining the whole process. And now you have provided the missing diamtere & thickness info...thanks again

prewar37 - Posted - 03/11/2009:  06:20:29

Slideman,
Be careful when you get the material. The 6061 aluminum alloy comes in different hardneses. You'll likely want the T-0. It's the softest. The material can be heat treated after shaping to make it harder.
Good luck,
prewar37

jaykellogg - Posted - 03/11/2009:  07:07:03

Actually heat treating aluminum makes it softer. When aluminum is made, it is cast into ingots and rolled flat. If you need a T6 temper, they will roll it to an intermediate thickness and heat treat it. Then, rolling to the final thickness also brings the temper up to T6. Also, when aluminum is rolled it acquires a grain in the direction it is rolled. It would seem to me for spinning it would be better to have a non grain material (if it is possible to get this). The grain of the material makes bending an issue. It bends better (less cracking) across the grain. If the bend is parallel to the grain it is more likely to crack. As you roll aluminum it gets longer, but no wider. I immagine the spinning operation will harden the aluminum somewhat. I suspect the better cones are pretty hard. If you watch Paul Beard's video he tweaks one of his cones and it rings and he tweaks another cone and it has a dull sound.

Heat treating aluminum is done in an inert atmosphere. That way it is bright and shiny when it comes out.

W. Jay Kellogg

prewar37 - Posted - 03/11/2009:  09:17:24

I believe it's called "aging precipitation heat treating". Heat to 350 degrees for 8 hours, then air cool = T6 temper.

suppliersonline.com/propertypages/6061.asp

The T6 alloy is difficult to bend without breaking because of the hardness. T6 does form better across the grain, but if it's formed soft, (T0), the grain directiion won't matter.
Keep on pickin' prewar37

Slideman1939 - Posted - 03/20/2009:  18:05:11

I got some additional info on diameter and thickness. The metal is #6061 alloy in T-0 temper. T-4 and T-6 is to hard.Not all supply houses have have #6061 / T-0 in the thiness needed. Thiness is .010 ( 10/1000th" inch).Supply houses sell squares typically. So you buy 12" X 12" squares and owner cuts it into 12" circles for lathe mounting. Metal spinning instruction ( 3 D.V.D.s) is mail order purchased from metalspinningworkshop.com. thanks to all for input. I have simply added the missing info on thickness and diameter.

prewar37 - Posted - 03/21/2009:  10:14:55

Slideman,
I made a good living as a precision sheet metal mechanic for 18 years from the early '70's til '90. You sound commited to this project. Thats' great! Be prepared for some frustration during the prototype stages. Good luck with your project and let us know how the progress is going. Feel free to contact me via e-mail, if I can help I'll be glad to.
If I recall correctly a good finished cone should 'tap tune" to a F or F#.

keep on pickin', prewar37