chassis material choice

[Randall]

Steel or aluminum for your chassis, and why?

[soundguruman]

If you have a close look at aluminum vintage chassis, you will know why you should be using steel.
The weight of the transformers eventually caves the chassis. It takes some years but it happens.
There are reenforcing techniques for aluminum to prevent it from slowly bending. But it's expensive.
The production chassis available does not utilize those methods...
Steel is superior, much harder to machine, subject to rust. But I would rather have steel, or stainless steel.
And steel should be triple hot galvanized, AFTER the holes are drilled and parts test assembled.
I would have stainless, gold plated, if I had the choice. Stainless being the ultimate PITA to machine....
But stainless is my favorite material. If I go to all the trouble, why not use better material?
There are a lot of vendors selling aluminum, and they tell you it's great, but I don't buy it.

[J M Fahey]

Steel or aluminum for your chassis, and why?

If you are a factory with the proper machines (think Peavey/Fender/etc.) iron is fine (calling it steel is slightly overblown).
For homebuilding , if you have to punch holes (not drilling which is easy), stick to aluminum.

If you choose sensible thickness (2mm - 3/32") , it will last forever.

As a real world example: this is a 200W power amplifier I built in 1972.
2 mm aluminum simple "U" shaped chassis, supporting a *huge* power transformer, still going strong and in weekly use for the last 40 years.



or consider all modern SS Fender amps (Princeton 112/Performer/whatever) built on much thinner aluminum chassis (1/16" or thereabouts).
Not as old as mine but definitely been around for at least 12 or 15 years ; AFAIK I have never seen a cracked or even bent chassis nor read about any complaints.

Yes, on tube amps (HRD, etc.) they use iron, it also works fine.

EDIT: looks like today is not "Attachment Day".
No picture or upload sticks.
Oh well.

[soundguruman]

If you are a factory with the proper machines (think Peavey/Fender/etc.) iron is fine (calling it steel is slightly overblown).
For homebuilding , if you have to punch holes (not drilling which is easy), stick to aluminum.

If you choose sensible thickness (2mm - 3/32") , it will last forever.

As a real world example: this is a 200W power amplifier I built in 1972.
2 mm aluminum simple "U" shaped chassis, supporting a *huge* power transformer, still going strong and in weekly use for the last 40 years.

[ATTACH=CONFIG]23536[/ATTACH]

or consider all modern SS Fender amps (Princeton 112/Performer/whatever) built on much thinner aluminum chassis (1/16" or thereabouts).
Not as old as mine but definitely been around for at least 12 or 15 years ; AFAIK I have never seen a cracked or even bent chassis nor read about any complaints.

Yes, on tube amps (HRD, etc.) they use iron, it also works fine.

EDIT: looks like today is not "Attachment Day".
No picture or upload sticks.
Oh well.

Aluminum is for wimps.

[J M Fahey]

Aluminum is for wimps.

Hi soundguruman

You weren't heard for a couple weeks and I was worried you had passed away.

Nice to know the resident dick is still alive.

[Randall]

I had a little VOX modelling amp in for repair a while ago. It was dropped during shipment and the transformer pulled the chassis away to the point of the buttons not working. It was so thin I could bend it with my hands. But, thickness is not really what I am wondering about, it's more about does the material itself make much difference.

[J M Fahey]

Very short answer: Thickness *and* material are both important.
You can't consider just one of them.
"Weaker" material, if thicker, ends up being *exactly* the same strength.

Short example: 2mm aluminum (which I use for my chassis) is *way stronger* than 1 mm CRS, cold rolled steel , which is the typical material used for "iron/steel" chassis.
How's that?

Here's what a boat designer says, comparing aluminum hulls to steel made ones:

Mind you, he's no "wimp", but analyzing "Titanic" type hits at high speed to hard objects in the water.

as in:

Is There a Difference?

The question has been asked: "What about rocks and ice and things that a boat can run into? Does either steel or aluminum provide an advantage in a real-world sense?"
..........
This page offers a bit of additional information regarding the relative strength of the two materials. This brief article is intended only to be a general way of viewing steel and aluminum as they are used in boat structures.
..........
As we will see, the issues of strength are tipped somewhat in favor of aluminum, mostly for the reason of its lighter weight. Being much lighter, aluminum will permit a more robust structure within any given weight budget.

Built to the Same Standard

An aluminum hull structure, built to the same standards, weighs roughly 35% to 45% less than the same hull in steel. As a result, if high strength is of the highest priority, the alloy boat can be built to the same structural weight as the steel vessel, and then be considerably stronger.

For the sake of an easy example, what would be one inch of plate thickness on a steel vessel would be approximately one and a half inches of plate thickness on the aluminum vessel in order to achieve the same rigidity of structure.

But of course the choice is yours.

Why then do most manufacturers still prefer steel?
1) because it's cheaper
2) *if* you already have dies and presses, it's slightly cheaper to work steel.
3) iron is easily spot resistance soldered (the "dimples" you find joining parts) which is fast and cheap , while aluminum must be "mechanically" joined (screws/bolts/rivets) which is more expensive.
4) in large batches, galvanizing is very cheap .

Why do homebuilders prefer aluminum, if they make their own chassis?
1) it requires lighter cheaper tooling.
2) it requires no surface treatment , does not rust at all.
3) if you need painted/silkscreened front panels and such, it costs exactly the same: blasting/sanding/brushing , phosphatizing , (oven) painting, silkscreening.

[txstrat]

I agree to the preferences of aluminum which Juan stated.
I've used 2mm U-shaped aluminum chassis' for 21 years. Even my first build still holds strong (no bending or whatever).
AND aluminum is a better conductor than iron, which is even better than steel (does this really make a difference in tube amps?).

Just my 0.02$

[Steve Conner]

I mostly use aluminium, but I make it really thick, like 3mm.

[txstrat]

I mostly use aluminium, but I make it really thick, like 3mm.

How do you punch (or drill) those tube socket holes? In lack of any pro tools I have to drill them with a power drill and a cone shaped bit of 32mm (max) diameter.
When I drill the holes for octal sockets the bit gets really HOT. If I try to avoid that and drill too slow the electric motor of the power drill starts to smell.

[J M Fahey]

For one-offs I use a "cup" saw of proper diameter.

For wimp aluminum any cheap one will do, so you don't invest a lot unnecessarily.

Just apply relatively light pressure, let the teeth cut what they will, you may apply a couple drops of lubricant (kerosene is fine and less messy than oil) or every now and then lift the saw and wipe a candle or some soap against the teeth.

[defaced]

From a mechanical standpoint, a chassis is a pretty trivial application - both families of materials can be, and have been, used successfully. Copy a design that's already proven for your (or a similarly sized) amp. If you're buying a pre-made chassis your goals/concerns will be different than if you're designing and fabricating a chassis from scratch.

Personally, I hate working with aluminum. It's an annoyingly soft material that I don't enjoy working with. I find working with steel to be much easier - including drilling large holes for tube sockets. Others don't find this to be the case, but to each their own.

-----

3) iron is easily spot resistance soldered (the "dimples" you find joining parts) which is fast and cheap , while aluminum must be "mechanically" joined (screws/bolts/rivets) which is more expensive.

Resistance Spot Welding. You look silly when you butcher the nomenclature and facts, especially considering how condescending you usually come off in your posts. Also, there's been a great deal for work put into RSW research of aluminum in the past decade - the automotive industry has a strong interest in perfecting RSW of aluminum - as does the martial producers who want to sell it to them (Alcoa). It can, and is, being done.

[Steve Conner]

I use hole saws, Greenlee chassis punches and step drills. (These are the offspring of a cone cutter and a Devo hat.) To drive the step drills I've used a 2-speed cordless drill on the low speed setting.

The only thing I find annoying about aluminium is how easily it clogs up files and saw teeth. I do my metalwork "ghetto style" with hand tools, so on the whole it suits me better than steel.

I once made a chassis out of 6082 aluminium, a much harder, stronger and better machining alloy than the stuff electronic project boxes are made out of.

[pdf64]

I've got a DrZ EZG50 on the bench at the moment, it's got a very high quality aluminum chassis, 2.5mm material, all joints / seems fully welded.
Reason it's with me is that it had an intermittent oscillation problem, especially when cold.
I noticed that the whole thing seemed microphonic when in that mode, just a tap on the front panel could set it off howling like a banshee (given gain and master set above halfway).
Tubes were fine, so on a hunch I clipped on an extra ground lead, from the board LTP ground return to the chassis; that got rid of it.
The grounding scheme uses a wire soldered on to the back of the control pots for the pre amp signal ground; no pot nuts were in any way slack, but that extra lead, or use of (seemingly) excessive torque on the nuts stopped the problem.
Slackening all pot nuts off brought the howling on permanently; weird thing is that the Vdc at the back of the pots stayed at 0V, whilst it was about 20vac.
To fix it, I've fitted an additional ground stud for the pre-amp, clamped up tight with star washers, as a belt and braces ground link.
As mentioned, the pot nuts were tight and the chassis (made in 2010) is still has a bright finish, no sign of surface tarnishing, so the cause of the excessive contact resistance is unclear to me.
Pete.

[loudthud]

The theory behind mechanical connections seems to hinge on making the connection "gas tight". Is there any kind of magic goo that will enhance the longevity of such connections?