Cast, forged, extruded, stamped

Greg Vincent · Post by **Greg Vincent** » 22 May 2002 3:21 pm

Hi folks,

Can some of you experts out there explain for me the characteristics of metal that has been a)cast b)forged c)extruded and d)stamped.

Specifically, which metals can be used in which process, what that process is (in layperson's terms) and what are the pros and cons of metal processed that way --especially regarding the construction of steel guitars. [Sorry if this sounds like a midterm question!

]

Thanks!

--Ignorant in L.A

[This message was edited by Greg Vincent on 22 May 2002 at 04:22 PM.][This message was edited by Greg Vincent on 22 May 2002 at 04:23 PM.]

chas smith · Post by **chas smith** » 22 May 2002 4:12 pm

Well, let's see here. Casting is where the metal is heated up to it's liquid state and then poured into a mold, typically, and then allowed to cool to the finished product. Forged is when the metal is hammered. In the old days, iron was heated to yellow hot in a forge and them hammered into a shape on an anvil, or two pieces of iron were heated white hot and them hammered together as a forge weld. Now days the metal block, typically steel, is heated in a furnace and then held between the two dies of a mechanical hammer, which can be very huge, and smashed into the finished shape. Extruded is when a metal bar, like 6063 aluminum is rolled and forced through the dies and squished into the final shape. Stamped is where sheet metal gets "cookie cuttered" usually while it's cold. The shapes are punched out with dies.

The properties of cast metal vary widely depending on what kind of metal and what alloy is used. The pedals on your guitar, the end plates and the necks, if it's an older guitar, were most likely cast, as was the engine block, and the mirrors in your car. The axle in your changer is likely to be cold roll steel, which is an extrusion as are the aluminum angles and bars and perhaps the aprons and pedal bar. The keyhead on your Stringmaster was stamped. I can't think of any guitar parts that might have been forged.

Forging and extruding are the most violent followed by stamping where the crystalline structure of the metal is upset and crunched together. In steel, for example, the molecules are compressed tighter which makes it harder, especially on the surface. The fact that the metal is compressed during forging and extrusion means that internally it's under tension which might make it less resonant. Old cymbals, which are spun (forced over a shape), that have been played and have had time to age, sound more resonant than new cymbals because the crystalline structure has had time to relax. When I made necks for my Super Pro, I machined them out of aluminum tooling plate, which is a casting that has been flycut.

This could turn into a dissertation...

Jon Light · Post by **Jon Light** » 22 May 2002 4:17 pm

...which I would avidly read. Thanks for the post.

Rich Weiss · Post by **Rich Weiss** » 22 May 2002 4:49 pm

Chas Smith: A+

Bill Ford · Post by **Bill Ford** » 22 May 2002 6:19 pm

Chas. my good man,very good,very acurate
very understandable.One would get the impresion that you were/are an engineer
(not train driver)of sorts...LOL
You are one of the ones that can always be depended on for great info.

Bill Ford

------------------

chas smith · Post by **chas smith** » 22 May 2002 9:55 pm

Gentlemen, thank you. Actually cold rolled steel as an extrusion is a bit of a stretch, it's more like a cold forging, but I had just finished talking about the heat and I didn't want to make a u-turn in the middle of the block.

I would also add as the pros and cons, before CNC, computer numerical control of machinery, casting was the easiest, read cost effective, way to produce complicated shapes. The cons of casting were/are porosity and contamination (there are elaborate ways to circumvent this, read expensive); now, many of the parts, keyheads, endplates, necks and some of the mechanical goodies underneith can be milled from blocks of aluminum, billet, on milling machines driven by computer controlled servos that have been programmed to cut those parts.

Greg Vincent · Post by **Greg Vincent** » 23 May 2002 7:03 am

Thanks Chas!

Your paper will be posted in the trophy case by the lockers as an example of excellent course work.

Actually, I'm printing out a copy and keeping it with my reference stuff. Great info!

If I can inquire further: Are castings considered "bad" in steel guitars? Is that what "pot metal" is?

-GV[This message was edited by Greg Vincent on 23 May 2002 at 08:06 AM.]

James Smith · Post by **James Smith** » 23 May 2002 11:27 am

There is another way of mass producing complex shapes out of metal. Powdered metal can be pressed into complex shapes in a mold and then heated (sintering) which fuses the particles together. Therefore you can have the strength of a ferrous casting without expensive machining of a rough casting. Also, if the part is to be used where lubrication is required you can mix graphite with the powdered iron and the part will self lubricate as it wears.
Another interesting thing about the extrusion process is the euctectic points . That's a temperature range where the metal is not solid , and not liquid, kind of like jello. When a metal is in this state it can be forced through a die and make a long piece with a cross section the same as the die. I think most of the modern pedals on a psg are made like this. Another thing, if the part needs to resonate (neck for example), I think it should be manf. the same as a high quality bell, by casting.

chas smith · Post by **chas smith** » 23 May 2002 5:22 pm

Are castings considered "bad" in steel guitars? Is that what "pot metal" is?

About 15 years ago I called Paul Franklin Sr. to talk about a guitar that I had, not a Franklin, that didn't sound very good, to get his opinion on what I could do to improve it. He said, "You have to think of the guitar as all 'circles', that every part of the guitar affects the way it sounds, even the pedal board". There was a pause in the conversation while I pondered that, and he said "you don't believe me, do you". I think I said something like, I don't doubt you for a minute, it's just that that had never occurred to me. He said "go strum your bass strings and touch the pedalboard, if its vibrating, its part of the sound". Needless to say...

So one could make a compelling argument that every part of the guitar should be as resonant complementary as possible and castings tend to be more resonant than extrusions so in that regard they would probably be preferrable--see James above--. It was part of the reason I used tooling plate, the other was I wanted solid necks on the SP. (I also made solid necks on my Dekley D12 which weigh 17 lbs, the concept at the time was to make the necks as self sufficient units and to be able to function without the guitar body. It was a nice idea at the time. The E neck improved, the C neck didn't and I need a forklift to pick up the guitar)

To be realistic, the difference between a cast neck and one machined from an extruded bar is probably nitpicking and it's likely that the difference wouldn't be all that noticeable, but I wasn't able to do an A/B. I remember reading an interview with a famous guitar player who was saying that the brand of battery in his stomp box made a difference in his tone. That guy must have Superman ears.

Pot metal, white metal, is basically zinc, which is relatively soft and weak, doesn't corrode under normal conditions, is easy to cast, which also makes it brittle, and can be chromed, to play to our small shiny object fascination. It's the reason the knee levers broke off on my Super Pro and the reason it didn't sound as good as it could have, changer fingers.[This message was edited by chas smith on 23 May 2002 at 06:38 PM.]

Winnie Winston · Post by **Winnie Winston** » 26 May 2002 8:26 pm

Charles says (about extrusion), that it startes as a flat and is rolled...
This is NOT so.
In the extrusion process, the aluminum is fed into the hopper as tiny bits. The material is then heated until "pasty" and is forced through a steel die that is the shape of the final product in section. Thinbk of an old screw meat-grinder-- or even the toothpaste that comes out of the tube when it is squeezed.
THAT is extrusion. One of the advantages is that you can make very long pieces of consistant section.
You can also extrude variying alloys of aluminum-- from very soft to very hard. The 2024-T6 which I used for most of the parts on the steel I built was a nice compromise of hardness and workability. One of the advantages of extrusion is that the molocules of material line up and form a very strong structure.
Any material that can be melted to a putty consistency can be extruded-- plastics are the obvious other material that benefits from this process.
The advantage is that the tooling is fairly inexpensive for a "one off" part-- like a foot pedal-- just extrude the outline shape, and slice them off at 1" thicknesses.

Winnie

chas smith · Post by **chas smith** » 26 May 2002 9:46 pm

I stand corrected.

Henning Kock · Post by **Henning Kock** » 27 May 2002 1:23 am

May 27, 2002
Regarding what type of metal for the steel guitar neck:
Think about a cast church bell with billions and billions small air bubbles in the metal, and then a big rolled steel plate used on theatres for the sound of thunder.
Which of the two has the best sound ? ...
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Henning Kock
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Henning K. Music
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DK-8300 Odder
Denmark,
Europe
phone 8654 2959
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[This message was edited by Henning Kock on 27 May 2002 at 02:25 AM.]

Rick Collins · Post by **Rick Collins** » 27 May 2002 8:31 am

Henning, what you say is quite correct for the bell being struck by the clapper or the metal sheet being struck by perhaps, a hammer. The porous metal casting of the bell has a much more pleasant tone;___good analogy.

But consider this:

Would we necessarily conclude from the same comparison, that this would apply to the wood also, in the construction of a steel guitar? My first inclination is to say no, when I think of a soft wood like the trunk of a palm tree, which has a loose grain, as opposed to that of a maple tree, which has a very tight grain. But if I use the above comparison (of metals), I must conclude that the palm tree wood is best for musical instrument construction.

Maybe the key word here is struck. But on a stringed instrument, the strings are plucked sending the vibrations throughout the instrument. There is no striking of the construction material. How would a violin sound constructed from the wood of a palm tree?

What conclusion can be drawn here? I don't know;___maybe none.

Rick

chas smith · Post by **chas smith** » 27 May 2002 2:56 pm

Think about a cast church bell with billions and billions small air bubbles in the metal, and then a big rolled steel plate used on theatres for the sound of thunder. Which of the two has the best sound ? ...

You can't really compare them because one has a bell shape and the other is a sheet, so they vibrate very differently. If you had a bubbly sheet the same dimensions as the steel sheet, it might not sound as good.

I have several titanium 6-4 thundersheets that are very impressive sounding. The alloy has a lot to do with how, whatever-it-is, is going to sound.