Aluminum vs steel chassis. Pros and cons

Hints-

1) Use a lube when drilling aluminum, either a proper cutting oil like Cool-Tool II (veggie based), or at least a squirt of WD-40. That's one place the stuff shines. Works great for milling aluminum too. For steel, use the oil.
2) There are different grades of aluminum. 3003 is gummy, 5052 is better and bends well, but IMO, still gummy and drill bits can grab and you get lots of burrs. 6061 is nice but harder to bend. There's a nice list and table here- http://www.clintonaluminum.com/which-aluminum-alloy-bends-best/
3) Use step drills when you can. Sometimes drilling a small hole and bringing it to size with a tapered service reamer (Google it) works better.
4) To get holes exactly where you want them, lay it out with a good scale and scribe, or height gage. Dykem blue is standard for visibility but magic marker works OK. Next, center punch with a plain one or automatic spring loaded one, but use a magnifier and get the punch dead on the mark. Now, spot the hole with either a spotting drill, a small center drill or a small drill bit, small enough not to wander from the punch divot. Finally, drill the hole. Done properly, even with primitive tools, you can get a hole located to about 0.01" with no problem. Skip a step and all bets are off.
5) Don't thread thin aluminum. Get some PEM nuts. You'll need a decent vise or levered pliers to put them in, and the hole size is critical, but the end result is way more professional. No more stripped out threads!
6) Don't forget safety. Clamp what you're doing or block it from rotating. Drill presses account for a lot of accidents, especially when doing sheet metal.
 
Much easier time working w/ aluminum. AS ConradH said, use sharp drills, a little liquid on the drill. One thing I like is w/ aluminum you can use a step-drill to cut larger holes, just turn it real slow and no problems. My last build was a piece of 3031, and yah any holes under .250 really mushroomed really bad, and had to be cleaned up w/ de-burrer.
The other thing is you have many places on-line you can buy piece-aluminum in varying thickness and types, for short money, shipped right to your door.

One other thing: if you want a "bent chassis" i.e.: edges folder over and a lip underneath, Find a HVAC shop who does their own duct work. Depending on the type of brake they have, some can do the double lip, some not. Keep looking. I have one that has a finger-brake, and for a case of beer, they'll bend a chassis for me. :):):)

My 2 cents... Stu
 
Why does anyone solder to the chassis?

Never had a mechanical chassis ground get flaky? Thats why I solder to the chassis. The solder doesn't get oxidation between the parts. The small current levels dealt with in an audio amp are rather a different matter than NEC safety grounds.
 
Never had a mechanical chassis ground get flaky? Thats why I solder to the chassis. The solder doesn't get oxidation between the parts. The small current levels dealt with in an audio amp are rather a different matter than NEC safety grounds.

Well, sure, I have had this problem with old equipment. Which is why I clean the contact area, use a high-quality, low-resistance fastener of a similar metal, and make a solid mechanical contact. And it never goes bad. Same thing for soldering, where I make sure the contact is mechanically sound and able to carry current and weight on its own.

I have seen far more poor quality solder joints than corroded bolted contacts. That is a general rule, particularly for the 1950s and 1960s era kits. It's tricky to solder to a chassis because a cold joint can be weak and not fail for some time even when it appears to be ok. Welding is much better. Using a bolt and a lug that's tightly fashioned is better yet.
 
Most of my gear is 50s era riveted stuff, and those can be a real pain for noise chasing. What I've usually done to fix the problems is to simply solder the tabs under the rivet so it stops acting up. I own two amps that this was done by the factory on, my copper plated Sherwoods. The one and only connection that was mechanical only in the S7000 phono section is of course the one source of noise that it had. Bit of solder sorted that right out. Can't weld tinned copper terminal strips, and you aren't doing it in a populated chassis besides.
 
Most of my gear is 50s era riveted stuff, and those can be a real pain for noise chasing. What I've usually done to fix the problems is to simply solder the tabs under the rivet so it stops acting up. I own two amps that this was done by the factory on, my copper plated Sherwoods. The one and only connection that was mechanical only in the S7000 phono section is of course the one source of noise that it had. Bit of solder sorted that right out. Can't weld tinned copper terminal strips, and you aren't doing it in a populated chassis besides.

Agreed, one cannot weld a populated chassis if one ever expects anything on it (or nearby) to ever again properly work afterwards.

But there is a reason that manufacturing codes and contracts specifies crimped and screwed or riveted connections over soldered ones: safety and reliability. Unless the soldering is of high quality—and I'm certain yours is given the volume of gear you've rebuilt (no snark intended, that's respect for your rebuilding work)—the joint will be weak and will degrade over time. A non-acid solder does not do a good job of etching the surface and so the joint is not as strong as the environment dictates. I've seen many chassis soldering joints which fractured and failed because of this. I've also seen many that remained excellent fifty years later.

Much of that has to do with the mass of the soldering iron. Getting the chassis really hot at the junction point is critical. The old style soldering torches or the heavy duty electrical ones (the ones with a heater the size of a cigar and a tip the size of an asparagus spear) can put out enough heat to get a nice connection. Old radios have soldering work like this. That soldering will even survive the apocalypse, even though not much will be on AM radio then. The amount of heat dumped into that connection when it was formed was prodigious.

As a general rule, and from what I've seen in commercial equipment, hand soldering has always been highly problematic. Even for commercial manufacturers prior to wave soldering machines. (Those of you who have Sony gear know of what I speak. Who thought up those nightmare wiring harnesses with bad joints.) I've touched up many joints that outwardly appeared fine and had noise and thermal problems suddenly vanish.

The rivets you speak of were known to be problematic because of a galvanic reaction. Anytime two dissimilar metals (like copper and steel) are in contact they act like a battery and corrosion results. So it isn't the case of a steel on steel rivet going bad, as that tends not to fail despite the passage of tens of decades. If they did fail, all of NYC's bridges would fall down, and the subway vaults would collapse. Instead, we rely on hundred-plus year old infrastructure which mostly works. (Except on the L train whose tunnel was submerged during Sandy.)

Here's some photos of galvanic corrosion in copper rivets in steel and steel rivets in copper:

Pretty impressive. Of course, they did add some chloride to the mix...
 
yeah, needs a lot of heat to have much hope of it holding. Chassis soldering is a pain honestly. I really could use one of those big mother irons for it when needed. As it is, I tend to use both my Hakko 888 and the 808 desoldering iron together to get enough heat to make it go. One of those big honkin American Beauty irons that look like they should be used for branding cattle would be a lot more effective.

When I did the Bogen 100A's, the only chassis ground connection is actually a mechanical one. I don't really much like grounding to the chassis, but when you're dealing with old stuff that isn't practical to re-work the grounding on sometimes you don't have a lot of choice in it.
 
One of those big honkin American Beauty irons that look like they should be used for branding cattle would be a lot more effective.

Yes, one of the old Ungar ones! 50 W and 1,000 ºF of pure lead-melting goodness.

(In Aussie voice) That's not a soldering iron. (shakes head) This is a soldering iron. (nods head)
 
I have a huge iron stashed away somewhere that I got from a bin at the auto store a few decades ago for about $8. Has an angled 4-sided tip about 1/2 inch in diameter and is probably 100 watts or so. Not good at all for SMT.
 
I hear you on the SMT stuff. Last week I was installing a new saw and after I got it up and running I had to switch it out of Metric mode and into inch mode. I called the service department for info and they told me to flip dipswitch #2 contact #3 to On. Well I looked for dipswitches on the circuit board and couldn't find any. Called back and while on the phone they directed me to the exact area on the PCB were they would be found.
Did you know that they now make super tiny teeny weeny dipswitches that are SMT's? Had to use a strong magnifing glass just to find the switch I needed to flip. Than you need to use a pointy object to slide the lever.
When will this crap end?

BillWojo
 
I have a huge iron stashed away somewhere that I got from a bin at the auto store a few decades ago for about $8. Has an angled 4-sided tip about 1/2 inch in diameter and is probably 100 watts or so. Not good at all for SMT.

Depends on what you consider to be "surface-mount", now doesn't it?

I have a collection of the old 1950s copper-head soldering irons heated with a torch. Like these:

But for chassis soldering, if one's chassis is made out of 10 gauge steel, one just can't beat the disposable thermite-charge soldering iron:
Now that is a soldering iron to end all soldering irons. I wouldn't want one of those in my home under any circumstances. Seems like a great way to void one's fire insurance and burn the house down at the same time. (The cartridge uses a percussion cap to ignite the thermite charge.) See:
 
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An aluminum chassis gives you an easy way to heat sink voltage regulators you might use to provide DC to phono preamp tubes' heaters, and such.
 
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