chassis material choice

[Steve Conner]

Yes, it's used for heavy crimp connections on overhead wires in the power industry. One brand is Aluma-Shield from Thomas & Betts.

[loudthud]

In the US back in the 60's aluminum household wiring was used. It was promoted as being equivalent to copper, you just had to use a bigger size to get the same current rating. UL labs "approved" it. It didn't take long for some of the houses to catch on fire. This was blamed on the outlets not being compatible so special fixtures were designed with a special mark that could be used with AL wire. I think some white goo was supposed to used to coat the wire before is was inserted into the fixture, this retarded corrosion at the point of contact. Is this the same stuff?

Most if not all of the wire that "flys" is aluminum. It is spliced to copper wire at the weather head for the vertical run to the power meter and service entrance.

[Mick Bailey]

I use aluminium, with a home-built chassis bender that produces neat folds. I've also used stainless for hi-fi enclosures where the chassis is visible, but the bends need a lot more force to produce a tight radius and they need considerable 'over-bending' so that they spring back to 90 degrees.

Commercial chassis now use Zintec. I don't think I've ever seen a hot-dipped chassis - I would expect serious distortion and a reduction in hole diameter as well as infilling with a triple dip.

You can fabricate a really strong chassis using a thicker top plate (say, 3mm) and use angle or channel section for the sides. Looks pretty neat if you use hex countersunk screws. A lot can be achieved using basic hand tools, careful marking out and not hurrying.

If your cutter is overheating then use either a cutting lubricant for aluminium (I have a tin of Trefolex bought 30 years ago and still in use), kerosine (paraffin in the UK), or rub a bar of soap on it. Friction causes the heat and indicates thet the cutter is rubbing as much as cutting.

Lube will give you a better finish as well. Just ask the girls at the bar.

[J M Fahey]

Quote Originally Posted by J M Fahey View Post
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.

Huh ???
Ever heard of explaining things in terms so the answer is actually understood by the asker?
Do you think that I should have answered "steel chassis use RSW" and leave it at that?
Gimme a break!!!
This place is mainly to try to help others, not building a "guru" reputation or something.

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.

Great for the Automotive Industry, but we are in MEF discussing home working of amplifier chassis, not some Formula 1 car construction.

Besides, what do you think is most likely to be found at a typical home builder "shop"? a Pop riveter or an ... "RSW" ?

[bob p]

Steel or Aluminum? How about really heavy gauge copper? Some of the best gear was made this way back in the Golden Era. Motorola consoles come to mind as having a really nice copper chassis. Today Cu is just too expensive.

Given the choice of Al vs Fe, I'd rather have a sturdy iron chassis and deal with the fact that it's harder to machine. You'll need carbide tipped drill bits and greenlee punches. Aluminum would be OK if you could get nice, heavy aluminum. Unfortunately, the commonly available offerings from companies like Hammond and Bud are just thin and flimsy. If I'm going to use a Hammond, I prefer iron. If I can get a custom chassis made to spec by a metal shop, heavy aluminum, with reinforced corners, would be nice.

[Mick Bailey]

Carbide tipped drills wouldn't be my choice for DIY drilling of steel. The helix and rake angles needed to cut steel result in a fragile bit that easily breaks if the workpiece vibrates or isn't supported, or when the drill breaks through. HSS is a better bit material, the main consideration being to lubricate the drill and to rotate it at it's correct speed for the material being drilled. They're also easily resharpened and will last for years. Then you can make a centre punch out of them when they're finally ground down to a stump.

A problem with mild steel for the DIY builder is that you need to use electro-zinc coated sheet (Zintec or other brands), otherwise you'll need to apply a protective coating, or have it electroplated afterwards. If you begin with coated stock, the mechanical handling, marking, cutting, bending etc scratches the surface and it looks poor. You can't rub it back to refinish it or take out marks. Industrial processes are designed to maintain the integrity of the coating and minimise damage.

For me, aluminium is the material of choice for the average builder.

[Mick Bailey]

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.

The surface of aluminium immediately forms a highly insulating intrinsic oxide layer when cut or exposed to air - even if the metal looks bright. I wonder if the pot nuts hadn't bitten into the surface - had they used plated star washers behind the pots?

[pdf64]

The pots didn't have star washers.
I think they were Alpha brand, the threaded bushing was rather short and with the thickness of the chassis material and front plate, there was only sufficient thread available for the nut and a thin washer between the nut and front panel.
Just to note, the oscillation stopped when the global negative feedback loop was opened; the pre-amp was additionally tied to ground at the reverb output RCA socket (2 ground leads from V3 reverb recovery/mixer shared cathode ground return, one to the RCA socket, the other to the pot bodies).
Pete

[Wittgenstein]

After trying a few different materials I ended up settling on stainless steel. It is kind of a bitch to tool but it is lightweight, strong and does not rust. I add a bit of oil to my Greenlee punches and they seem to be holding up well.

[J M Fahey]

Nice builds, congratulations.

Now we deserve gut shots, I guess

[Mick Bailey]

Here's a small Hi-Fi amp (a relative term, but compared to MP3 quality my cement mixer is Hi-Fi) built many years ago to test out some ideas. It was built pretty shorlty after I fabricated a bender and is folded from 1.8mm aluminium sheet, including the rabbit hutch on top. I tried the same in stainless and couldn't get the crispness of the bends.

Incidentally, it's still in use; despite the inferior spec, low output and tiny OPTs. It sounds wonderful.

[Tom Phillips]

That is some really nice sheet metal work Mick. Especially for a self fabricated bender.
Tom

[soundguruman]

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.

Well it wasn't me who passed away. it was my mother. 91 years old...
The last few mouths, she couldn't stand up or walk, or wipe her own rear.
Myself and the caregivers, doctors, nurses, hospice, had to do that for her. It was 23 hours a day minimum shift.

But getting back to the question...just for discussion sake...
aluminum is a terrible choice because #1, it oxidizes, and overheats, as an electrical conductor.
So much, that it's been banned for residential uses. In fact, as a conductor, banned for most other uses too...
Although at one time we were told how great aluminum wire is, it failed miserably as a conductor of electricity. And you want to ground you power supply to "that?"
But I guess we would all be using aluminum wire, to wire our amps, if it was so great...but we don't, thankfully.

#2 you can't solder to aluminum.
#3 it's too soft to hold shape.
If you noticed, Marshall built their first prototype tube amps using aluminum chassis. The transformers sank into the craters...
As you can see, they did not continue using aluminum. It just can't stand up to being road-worthy. Not strong enough to withstand the abuse of touring.

Even the smallest Fender tube amp was always built on steel chassis. Although aluminum was easily available. Guess why?
Even your fake "Vox," "Ampeg" etc...etc...(all made in China or Vietnam) tube amps are on steel chassis. Why not aluminum? Even the imitators wanted steel.
Let's see your aluminum SVT! Hahahahahahahahahahahahhhh!

[J M Fahey]

I started writing my answer with "Ouch!! I'm sorry about your Mother!! " and leave it at that but kept reading and found you still are the same insensitive dick as you always have been, so I deleted it, absolute waste of time.

It's hard to feel sorry about you, because you make such an excellent job about erasing any such feeling.

I'll Pray for your Mom, but it's absolutely unrelated to you.

[bob p]

I understand that some of you guys might not be fond of one another, and that's not really my business. But when you guys go slapping each other with personal attacks in these public threads, you end up making it everyone's business by throwing it in our faces. Please do us all a favor and move the nasty-grams to emails or private messages so that the rest of us aren't forced to suffer from exposure to them. They really don't serve a useful purpose for the threads or for the forum, and you guys have all been around here long enough to know better. I have a lot of respect for you guys, but your behavior right now really surprises me. I know that you know better than to behave this way, so please resist the temptation to lash out at one another in public. Please?