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Thread: Chassis Design

  1. #1
    Member broken flyer's Avatar
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    Chassis Design

    Hi, I'm going to start building a tube amp soon and i've got some questions i was hoping someone would have the answers to. I'm building this amp completely from scratch. I'm going to start by making my own chassis then my own cabinet and then ill wire it up. I'v got the cabinet all figure out, it'll be made out of 3/4" pine, then covered in tolex, however im not sure whats the best way to go about the chassis. I was going to make it out of 16 gauge steel and then weld it with a MIG welder, however it was brout to my attention that my dys for cutting out the holes for the components might not go threw 16 gauge steel, so now im considering aluminum or maybe just some thinner steel. maybe 20 gauge steel or so. Have any of you built your own chassis before? if so, out of what and how thick? If i opt to do aluminum how thick should i make that? Any helps appretiated, thanks in advance.

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    Old Timer soundguruman's Avatar
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    16-14 gauge steel. Aluminum chassis are flimsy and don't last. Yes, weld the steel together, then have it triple galvanized, after all the holes are cut.
    There are plenty of components designed to mount in a thick steel chassis.

  3. #3
    Old Timer defaced's Avatar
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    Quote Originally Posted by broken flyer View Post
    Hi, I'm going to start building a tube amp soon and i've got some questions i was hoping someone would have the answers to. I'm building this amp completely from scratch. I'm going to start by making my own chassis then my own cabinet and then ill wire it up. I'v got the cabinet all figure out, it'll be made out of 3/4" pine, then covered in tolex, however im not sure whats the best way to go about the chassis. I was going to make it out of 16 gauge steel and then weld it with a MIG welder, however it was brout to my attention that my dys for cutting out the holes for the components might not go threw 16 gauge steel, so now im considering aluminum or maybe just some thinner steel. maybe 20 gauge steel or so. Have any of you built your own chassis before? if so, out of what and how thick? If i opt to do aluminum how thick should i make that? Any helps appretiated, thanks in advance.
    People who don't work with steel on a regular basis find that because it's so much different than working with wood that it's " hard". If you take a drill bit and blast it full RPM on a piece of wood, you get a hole. You do that with a piece of steel, and you get a seriously dulled or broken bit. Normal every day sheet steel is no harder to work with or drill than wood, the rules are just different. I have used elcheapo Harbor Freight step drill bits to drill octal sockets in 16g steel. When I was done, the bit was as sharp as when I started. Use pilot holes, drill slow (RPM), use oil, clamp stuff down. If you're not getting a chip out of the hole, stop, you're doing it wrong.

    If you do have the chassis galvanized after you fab it, account for the thickness of the galvanizing when choosing your hole sizes.
    -Mike

  4. #4
    Old Timer soundguruman's Avatar
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    WELD some grounding lugs to the chassis, one at the power supply, one at the preamp ground, one at the power AC safety ground, before galvanizing.
    Don't try to solder grounds to the galvanized chassis. Avoid, if possible, screwing ground lugs to the chassis. The soldering will produce toxic fumes, and a superficial ground connection.
    Get your grounds welded deep into the metal.

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    Old Timer J M Fahey's Avatar
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    Hi Broken Flyer.
    I have been home building my own chassis at home, for around 40 years.
    Have metal shears, folding and punching brakes, etc.
    In fact, in this very moment, I'm fabricating 20 front and back panels for 100W SS amps.
    By tonight they will be finished, painted, silkscreened and punched.
    If I had ordered them, I would have to pay a lot and wait at least 15 days.
    For small scale production I found aluminum much more practical.
    2mm is thick enough.
    Fold a C (or U, itīs the same) shaped chassis and add reinforcing ends.
    If TIG or MIG available, solder them along the edges (best); if notPop rivets are better than nothing.
    For a single chassis with minimum tools you can use hardwood ends.
    The *big* advantage is that it does not rust, so you are not *forced* to galvanize or blast/phosphatize and paint.
    And it can be easily worked with "wood" or lighter type tools.
    Iīll take some pictures and post them tomorrow to show you how easy it is.

  6. #6
    Old Timer soundguruman's Avatar
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    Aluminum chassis collapse under the weight of the transformers.
    Take a look at Marshall prototypes that were built 40-50 years ago on aluminum chassis.
    They look like a pile of melted butter.
    Now look at the steel chassis that were built 50 years ago, or longer. Bingo.
    If I am going to invest a huge amount of time and effort into building a guitar amp from scratch, I'm going to invest in materials that withstand the test of time.
    Aluminum also oxidizes, and the resistance increases with time, which means the grounding fails.

    Aluminum is easy, cheap, and fast to work with, but it's a terrible long term investment.

    Nobody said that building an amp to last was going to be cheap or easy. Do it right the first time.
    "there is always time to do a job fast, but never time to do it over." -Gene Berg

  7. #7
    Old Timer J M Fahey's Avatar
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    MAYBE I work better than Marshall, then.
    My own aluminum chassis handmade in 1969 are still going strong .
    And all 10000 others built since.
    No oxidation or bad grounding problems either.
    While similar age iron chassis (including very well made triple plated Fenders) show different degrees of rust, from random spots to useless heaps of rust.
    Of course I shouldn't be taken *too* seriously, I'm based just on personal experience, not Internet folklore or drunk ruminations.

    PS: I'd LOVE to see some pictures of Marshall "pile of melted butter".
    So much that I'd spread it on my morning toast, go figure.

  8. #8
    Noodle of Reality Steve Conner's Avatar
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    Aluminium isn't as strong as steel, so you simply have to use a thicker gauge if you want it to support heavy transformers. Marshall probably used thin, weedy stuff, especially since they were prototypes and they probably couldn't care less if they lasted.

    Steel and aluminium both can corrode if unprotected. Steel much more so. Steel chassis have to be painted, chromated or nickel plated to stop them from rusting up and looking terrible, but you can get away with leaving aluminium untreated.

    Here is my modest contribution to the debate, made of 3mm thick aluminium plate. I think it is some high strength alloy like 6082 or 7075. As far as surface treatment goes, I used fine sandpaper to give it a brushed effect, and that was it. It still looks nice 10 years later.
    J M Fahey likes this.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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    Supporting Member Chuck H's Avatar
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    +1 for aluminum. The observation that aluminum "oxidizes" is true enough. But it implies that steel chassis don't?!? I'm pretty sure rust is caused by oxidation. And there have been easily as many ground faults on solder blob steel chassis as there have been on screw grounded aluminum. Just ask ANY tech that doesn't include "guru" in his personal moniker. I build many amps on the normal .044 aluminum chassis sold by Budd and Hammond. They are only a few years old but my personal experience tells me there isn't going to be any problems. My personal amp is built in an off the shelf Hammond chassis and I've been beating the tar out of it for five years with NO evidence of problems. I think soundguruman is just smaking based on some photo he saw. Or something like that. Any excuse to offer input. I'm guilty of that myself. Even recently. I mistakenly believed info from a book that I had no personal knowledge of and hadn't researched sufficiently for myself. It was embarrassing.

    JM was more graceful. But I would also be interested in factual documentation of the inferiority of aluminum.
    "I've heard magic defined as "a technology you don't understand". By that aphorism, the folks in this forum are practicing wizards, able to summon AND control the lightning demon, and make charms to allow others to use the demon in certain ways." R.G.

    "...less ear-friendly but handy for jazz." Leo_Gnardo

  10. #10
    Old Timer defaced's Avatar
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    The observation that aluminum "oxidizes" is true enough. But it implies that steel chassis don't?!? I'm pretty sure rust is caused by oxidation.
    Both materials oxidize. Actually all metals will oxidize depending on the circumstances. The difference is that *usually* (meaning in typical inland air environments) the oxide layer that covers aluminum is passive (Al2O3). Passive means once it forms, it doesn't continue to attack the metal. If you've ever seen aluminum with big patches of white powdery stuff, that's aluminum oxide that's done a little more damage than we typically see. Rust is the third oxidation state of iron, Fe2O3. Rust is an active oxide layer and that is the reason why once something starts rusting, it continues to rust.

    JM was more graceful. But I would also be interested in factual documentation of the inferiority of aluminum.
    As Steve pointed out, it's not a material issue, it's a strength and thickness issue. Neither material is inferior to the other, they're different and to be used for different things. A chassis is a such a light duty item (in the grand scheme of manufactured goods using each material) that it really is not hard to make one out of either material. The thing is one has to design (meaning do the loading and strength of materials calculations) to properly evaluate the options. It can get pretty deep or very simple depending on what assumptions you make and what your goals are.
    Last edited by defaced; 02-27-2012 at 01:03 PM. Reason: typo
    -Mike

  11. #11
    Old Timer J M Fahey's Avatar
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    To shorten an endless discussion, here is an equivalence table published by the guys at
    Sheet metal materials
    which *should* know what they are talking about.

    Please make a little mental gymnastics, column formatting gets lost with simple cut and paste, align columns with corresponding headers.
    In any case, the 2nd column gives steel thickness, the 3rd one aluminum thickness needed for *SAME* strength.
    40% more, nothing to write home about
    For those in doubt, check the original page mentioned above.

    Aluminum sheet vs steel sheet

    The following table gives a quick point of reference when you need the approximate thickness of aluminum sheet to use in replacing steel sheet.
    The designated aluminum thickness will give you about the same stiffness.
    Or, putting it another way, the deflection will be about equal.
    As a rule of thumb, plan on using an aluminum sheet about 40% thicker than steel.
    Since aluminum weighs only 1/3 as much as steel, this means that the equivalent aluminum sheet will weigh only half as much as the steel sheet it replaces.


    Approximate stiffness equivalence:

    Steel LB/SF Steel Thick Alu Thick Alu LB/SF
    .975 .024 .032 .452
    1.22 .029 .040 .564
    1.47 .035 .050 .705
    1.80 .044 .063 .890
    2.44 .059 .080 1.13
    2.56 .062 .090 1.27
    2.86 .070 .100 1.41
    3.66 .089 .125 1.76
    4.88 .119 .160 2.25
    5.49 .134 .190 2.68
    7.33 .179 .250 3.53

  12. #12
    Old Timer soundguruman's Avatar
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    Aluminum does collapse, now you know.
    It takes years for it to happen, but slowly over time, due to the weight of the transformers, it caves in.
    If there are no heavy items mounted, then it's probably acceptable.

    Considering conductivity, we (electricians) are no longer allowed to install aluminum in residences.
    The conductivity breaks down over time and it runs hotter and hotter.
    Last edited by soundguruman; 02-27-2012 at 02:41 PM.

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    Member broken flyer's Avatar
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    Thanks for all the replies. I have delt with metal before and have a shop full of tools, including mig and tig welders as im building this at my school, but i have punchs at home i was planning on using to put the holes for the components in the chassis and thats why i was was considering aluminon as well as i was thinking i could just leave it bare/just polish the face if i did aluminum. I don't want to spend the money and time to have it plated as by the time i had that done i could just go buy a pre-made chassis. I am more comfortable working with steel as far as welding goes, but right now im undicided how i should go about this.

  14. #14
    Noodle of Reality Steve Conner's Avatar
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    Someone ought to tell the power companies who use aluminium cables for their overhead lines. (with steel cores for strength mind you.) There's nothing wrong with the metal itself, the problem starts where it is screwed into terminal blocks. Because it is so soft and forms oxide easily, the connection loses clamping force, air gets in, oxidation starts, and you have another house fire.

    Only a newbie (or a hardcore vintage-ist) would use the chassis as part of the audio ground system anyway. You connect the green wire to the chassis for safety, and the audio circuit has its own ground bus (made out of copper!) that connects to the chassis in one place. If you aren't sending audio ground currents through it, it doesn't matter what it's made of, as long as it conducts enough to be usable as an electrostatic shield. (See Fender's aluminium foil pasted inside the wooden cabinet.)

    But if you really must use an aluminium chassis as a ground bus, those little toothed washers always did the trick for me.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

  15. #15
    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by soundguruman View Post
    Aluminum does collapse, now you know.
    It takes years for it to happen, but slowly over time, due to the weight of the transformers, it caves in.
    If there are no heavy items mounted, then it's probably acceptable.
    *IRON* does collapse.
    Titanium too.
    Like *everything* else.
    All it takes is going over its tensile strength limit.

    *IF* tensile strength limit is exceeded, (any) material collapses, slow or fast.
    IF NOT*, it does NOT collapse. Simple as that.
    At least in the Physics world .

    How do you avoid that?
    By *calculating* and *designing*.
    Which says that for any acceptable Iron design, simply using 40% thicker Aluminum is EXACTLY THE SAME.

    Considering conductivity, we (electricians) are no longer allowed to install aluminum in residences.
    The conductivity breaks down over time and it runs hotter and hotter.
    Tell that to Power Companies in the whole World, including USA, which rely more and more on Aluminum conductors in the heaviest Power transport problem there is in the known Universe, a.k.a. cross Country and Transcontinental Power grids.
    So far , none of them has noticed the effect you mention.
    Maybe they should hire you as a Consultant.

  16. #16
    Supporting Member Chuck H's Avatar
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    I was once told that all glass was in a continuing amorphous state. That's why the windows in really old houses are thicker at the bottom than the top... Then I noticed that the glazing continues to mate with the glass uniformly on these windows. So I asked a glazier about it. He said that the old, and not uniform, rolled glass was usually installed with the thick end toward the bottom just because that seemed to make sense. I doubt that aluminum is amorphous. but any factual research that could be demonstrated is welcome.
    "I've heard magic defined as "a technology you don't understand". By that aphorism, the folks in this forum are practicing wizards, able to summon AND control the lightning demon, and make charms to allow others to use the demon in certain ways." R.G.

    "...less ear-friendly but handy for jazz." Leo_Gnardo

  17. #17
    Old Timer defaced's Avatar
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    I doubt that aluminum is amorphous. but any factual research that could be demonstrated is welcome.
    It is absolutely not amorphous. It is a FCC structured solid. Here is a gorgeous micro from Wiki showing the grain structure. You can see the dendritic solidification structure, which you would not have in an amorphous solid as it doesn't have a crystal structure.

    http://upload.wikimedia.org/wikipedi...ace_etched.jpg
    -Mike

  18. #18
    Old Timer defaced's Avatar
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    Quote Originally Posted by broken flyer View Post
    Thanks for all the replies. I have delt with metal before and have a shop full of tools, including mig and tig welders as im building this at my school, but i have punchs at home i was planning on using to put the holes for the components in the chassis and thats why i was was considering aluminon as well as i was thinking i could just leave it bare/just polish the face if i did aluminum. I don't want to spend the money and time to have it plated as by the time i had that done i could just go buy a pre-made chassis. I am more comfortable working with steel as far as welding goes, but right now im undicided how i should go about this.
    From one welding guy to another, here's my advice. If you want to make this up out of aluminum, make it thick enough, and weld the corners. If I were doing a big amp, I'd make it in the 0.093 to 0.125" thick range, for a small amp, I'd probably not go any thinner than 0.063". If you're going to use a break to form this, keep the cold formability of the material in mind as well as bend radius and thickness. If you're going to weld it (like welding up the corners), pick an alloy you can weld easily like 6061-T6 (I'm not finding alot of love on its formability, so I don't know if this would be a good choice for the job). I don't know what your aluminum welding experience is, but I can help you out if you get in a bind.

    Or, you can fab the box out of steel, rattle can it, and use an aluminum veneer face plate. I know 16ga 1008 will work for this just fine for even big amp chassis.

    Personally, I'd choose steel because I absolutely hate working with aluminum. It doesn't bend well, I don't like welding it, I have to use special files and grinding discs to grind it. About the only thing it does well is drill and machine, of which I can do well enough with 1008 or 1018 steel so that becomes a non issue for me.
    Last edited by defaced; 02-27-2012 at 05:35 PM. Reason: I had teh most awesome idea ever. Even better than sliced bread.
    -Mike

  19. #19
    Member broken flyer's Avatar
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    Quote Originally Posted by defaced View Post
    From one welding guy to another, here's my advice. If you want to make this up out of aluminum, make it thick enough, and weld the corners. If I were doing a big amp, I'd make it in the 0.093 to 0.125" thick range, for a small amp, I'd probably not go any thinner than 0.063". If you're going to use a break to form this, keep the cold formability of the material in mind as well as bend radius and thickness. If you're going to weld it (like welding up the corners), pick an alloy you can weld easily like 6061-T6 (I'm not finding alot of love on its formability, so I don't know if this would be a good choice for the job). I don't know what your aluminum welding experience is, but I can help you out if you get in a bind.

    Or, you can fab the box out of steel, rattle can it, and use an aluminum veneer face plate. I know 16ga 1008 will work for this just fine for even big amp chassis.

    Personally, I'd choose steel because I absolutely hate working with aluminum. It doesn't bend well, I don't like welding it, I have to use special files and grinding discs to grind it. About the only thing it does well is drill and machine, of which I can do well enough with 1008 or 1018 steel so that becomes a non issue for me.
    Thanks... As of right now i have no experience welding aluminum, and i know it is quite a challenge especially using TIG. I'm going to practice doing some aluminum welding before i go ahead and try and make a chassis. I'm not going to bother with it if it'll be impossible to weld. I have a couple things i'm going to try and the first thing is i've got some aluminum wire for the spool gun mig we've got, and then after that i'll probably try some tig. I do have some aluminum rods for stick welding and i even have some aluminum brazing rods to use with a propane torch, so i've got lots of stuff im gonna try my hand at before making a decision. My dad had a guy from his work make him two aluminum chassis awhile back, out of some aluminum that was darn near 1/8th thick and he had trouble bending it. I'm going to be using a brake to bend this and i was planning on doing the standard fender U shape and weld up the ends however i'm just going to make it square instead of tapered like the fender ones for ease of covering the cabinet when i get to that part. My instructor told me that heaviest stuff our brake will bend is 16 gauge mild steel so that's what i have to work with. The only to reasons i want to do aluminum at all is so i don't have to finish the metal with something and then when i punch and drill holes for the components. My dad has a set of punches he's going to lend me when i do this and he's a little concerned that they won't handle going threw that steel. They'r the kind of punch you drill a pilot hole and the put the two halves on and then use a wrench to pull the the dye threw thew the metal. My instructor recommended i just make it out of 20 gauge steel as he thought that'd be plenty strong once bent up but i'm not sure as this is the first amp chassis i've built.

  20. #20
    Old Timer defaced's Avatar
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    You're welcome. Metal shop is what got me started in what I do for a living, so yea, it's cool you're doing this.

    If you can TIG steel, you can TIG aluminum. The skills are the same, it's reading the puddle and some of the prep work that's different. Steel you can see get red and want to drop out on you, aluminum just gets shiny, but you can't really see if want to drop out. Luckily, if you do this, you'll be doing outside corner welds, which are probably the easiest thing to do and make look good. Anyway, does your TIG machine have an AC setting on it? If not, you probably don't want to TIG this. DC aluminum is not fun to run, but it can and often is done. Before you run this stuff, check out youtube. One of the guys on the AWS forum was posting the other day about Mr. TIG having some lessons up which had really good video of manual Aluminum TIG. I took a quick peek through the videos and they look pretty cool.

    Stick aluminum is not fun, but I think it's a good thing to say you've tried. We also did some aluminum torch welding using a stick electrode as the filler, but never any brazing. That was cool because I like torch welding, but the weld looked like poo.

    Spool gun MIG aluminum, been a while since I've run that too. I remember it kicking off serious spatter and being really sooty to run if you drug the bead, but it was pretty easy. Wire brush the joint with a stainless wire brush and push the puddle. The crater will want to crack on you or drop out, so start up on the open end of the corner and push the bead to the inside corner. The terminology is kinda funny, but think of a pan and how the corners on the side are if you're welding them from the outside of the pan. I can sketch up a picture if it'll help.

    How big of an amp do you want to build? For steel, 20ga is pretty thin, but there are some tricks you can do to make it work. I think that's the thickness of the stuff we used to make tool boxes in metal shop. I'd measure it but it's 8 hours away right now.
    -Mike

  21. #21
    Member broken flyer's Avatar
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    I'm not going to build a very large amp. About the same general dimensions as a Princeton re verb just square. I'm trying to make it relatively light. It should be about 15watts or so and i'm going to use the lightest transformers i can find. It will pretty much be a Princeton reverb pre-amp with a deluxe power stage and then infront of the pre-amp i was going to put a tube screamer circuit as well as a rat circuit. I'm also going to leave out the tremelo funtion on the pre-amp for the sake of simplicity as well as space for the nobs for the two distortion circuits. I'm building the cabinet out of 3/4" inch pine. I've made a tool boxes in shop and if thats what 20 gauge is i think you're right on that being a little on the thing side. I haven't tig'd steel either and to be honest im not sure if the tig welder is AC. I've never had to use it and its not something they teach in the class. It's just sort of there if anyone wants to play around with it. I've spent most of my time on wire feeding steel but did do a bit of stick last year and i know i will not be using the stick on aluminum. I have watched a few videos on how to tig on youtube that were put out by miller and it looks very similar to oxy-acetylene. i was rather good at running beads with the oxy-acetylene so im hoping that'll help me when i get to give the tig a whirl. I think i'll have to find a piece of 16 gauge steel and try my punchs on them. If they work then i'll probably make it out of that then do a coat of gloss black/white trim on the face then do a clear coat over the whole chassis to stop it from rusting. I'm not sure how this would work but right now i'm thinking maybe a very thin coat of urethane might do the trick of getting it sealed up. Have you ever tried that?

  22. #22
    Old Timer defaced's Avatar
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    Damn, this is like talking to me 15 years ago, but instead of building amps, I was building bike ramps and grind rails. Our school was the same way, we had an old Lincoln in the corner that was never used for class, but if you knew you to hook it up and grind a tungsten, you could use it. I read two books cover to cover before I struck my first TIG arc, I think I was able to get both of them from the local library:

    Welder's Handbook: A Complete Guide to MIG, TIG, Arc & Oxyacetylene Welding by Richard Finch Amazon.com: Welder's Handbook: A Complete Guide to MIG, TIG, Arc & Oxyacetylene Welding (0075478012640): Richard Finch: Books
    Gas Tungsten Arc Welding by William H. Minnick (I have the older blue/purple covered edition, so you may find a copy that isn't yellow, but it's still the same book, just an earlier edition) http://www.amazon.com/Gas-Tungsten-A...0402437&sr=8-1

    Most TIG welders will have a big honkin switch on the front of them (if they're old transformer/rectifier styles, new ones are all different, but usually it's a small push button) that change from DC negative, to DC positive, to AC (if it has it). Sometimes there won't be a DC +/- switch, you have to swap the leads on the machine.

    If you can gas weld, you've got the hardest part of TIG welding already worked out, and that's feeding wire with your hand (it's actually easier when you TIG weld because you can use thinner gloves). Since TIG uses a foot pedal, usually what guys do is set the current on the machine for the max they want, and since the foot pedal is like a volume control, they just smash the pedal to the floor and give the arc the current they set on the machine. That takes the pedal out of learning to TIG weld, but I think you'll find it pretty easy to get the hang of.

    And yes, I used to urethane all of my welding projects because I hated painting. The wood shop had a nice spray booth, but you could only shoot their clear urethane in there, so that's what I did. For a clear coat these days, I use Rustoleum clear that I pick up at Lowe's. As long as you cover up the steel somehow, you'll prevent it from rusting.
    -Mike

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    I think there is a lot of good info here but for someone that really wants to build their own chassis this is my favorite method.

    Find a local sheet metal shop. Have them bend up a c or u shaped channel for you in whatever length they have available of .070 to .100 aluminum- personally I favor about .080" in 4 foot lengths. It should be darn cheap for the material and only two bends. Make sure the short part of the C is 2" exactly. You can then use a table saw (SLOWLY and CAREFULLY!) to cut it to whatever length (width, if you will) you need. A carbide blade makes a lovely cut and with a cutting sled it's very safe. Of course a band saw and a belt sander can also produce a nice edge.

    You want 2" height so you can purchase 2"x.5" aluminum channel from McMaster-Carr ($25 for 8 feet!) and box in the ends. It's easily welded if you like but you'll probably find the chassis is stiff enough that you don't need to- bolts or rivets should be fine.

    As mentioned above, hardwood ends are a great option, too. Plenty of Silvertone amps used wood ends and as a general rule it seems like the thin aluminum or crappy cabinet gave up long before the wood end caps. For that matter, didn't the marshalls with the chassis issues have thin off-the-shelf chassis? I've seen plenty of steel Fender chassis bent and destroyed too. Aluminum is more fun to work on and looks nice without any kind of finish which I like.

    I find that when building one-offs where things are likely to change, aluminum is the material to use!

    jamie

  24. #24
    Supporting Member Chuck H's Avatar
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    If I were building a 100W amp (which I never have) I would probably use aluminum thicker than the off the shelf chassis. I've commissioned .08 aluminum chassis and I found them prohibitively difficult to work with. The Hammond chassis look to be .051 for typical guitar amp sizes. I thought the one I built my personal amp on was .044. Well, I've used both then I guess. Holding up fine with no sagging or tearing. Easy to work with using drills, Dremel, nibbler and files. Polished up to a mirror like shine (no clear coat used) that has faded a little (due to oxide) but is still quite shiney after five years. If I removed the knobs I could have it back to a mirror shine in about five minutes using Crest toothpaste or silver polish.
    "I've heard magic defined as "a technology you don't understand". By that aphorism, the folks in this forum are practicing wizards, able to summon AND control the lightning demon, and make charms to allow others to use the demon in certain ways." R.G.

    "...less ear-friendly but handy for jazz." Leo_Gnardo

  25. #25
    Old Timer J M Fahey's Avatar
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    Let me add some practical experience.
    1) steel is fine, but you can't "just paint it".
    I make my own speakers , of course out of raw steel, prefer galvanizing (consider it, itīs cheap and good) but sometimes, in a hurry, I have to paint them ... properly of course.
    Raw sheet metal comes only covered with a thin layer of oil.
    You'll need to:
    a) wash and degrease it. You may start by wiping it with some gasoline soaked rag but the real degreasing comes with boiling or quite hot water and detergent.
    Any grease left: no adhesion.
    b) phosphatize it.
    This kills all rust dots that youīll certainly have , even in new stock, passivate the surface for better resistance and slightly etch it so that roughness allows paint to "catch" better.
    The industrial phosphatizing solution I use *also* degreases the surface: 1 step less.
    c) Paint it. Those dual purpose paints: anti oxide ("converters") + finishing paint are best. They save you 1 step.
    d) of course, you can have it powder coated.
    In that case those guys will do the cleaning too.
    Personally, if available, I'd have it galvanized.
    2) as you see, for a one off the aluminum route is shorter and smoother.

    Here you have one of my early amps, a 1972 200W RMS SS Power amp (*big* power in those days): still running happily after 40 years.
    It does have a BIG frigging transformer, consider the chassis is 19" wide x 3U high.

    2mm (.080") C bent aluminum:



    Does this work on tube amps?
    Have a look at my "Angus" JTM45 style amp.
    Still a C style, in this case 1.5mm (.06") aluminum.
    In this case, hardwood reinforced ends (I could have used some pop-riveted C reinforcements too)



    Handmade aluminum rackmount chassis



    Front view.
    Painting, silkscreening, all done in house:



    continues
    Steve Conner likes this.

  26. #26
    Old Timer J M Fahey's Avatar
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    C shaped "Bassman '59" chassis.
    Before definitive mounting, itīs closed with a backpanel which turns it into a box and adds overlapping side wings for rigidity.



    Same chassis mounted:



    Since we mentioned them earlier: my own speakers, galvanized blue (frames) and gold (back plates) simply because they came from different batches.
    For economy (since galvanizers charge me a fixed, minimum batch cost), I always make 100 backplates or 30/50 frames, depending on size.
    I pay peanuts per piece (say U$ 2 or 3 per full speaker).
    These are my version of Jensen C10R:



    My rackmount tube preamp, diriving 3 Ampeg heads (2 tube, 1 stereo SS) as power amps, each driving an 8x10" box.



    Itīs aluminum, yet it survives heavy Rock Band Tour conditions.
    Here itīs being used in Buenos Aires River Plate Football (you'd call it soccer) Stadium, 48000 seats.

    The Ampeg SVT400 seen below it, came to me brought by a desperate Bass player: it was a heap of rust (below the powder coating) and all ground connections were *very* poor or lost.
    A hum/hiss/RF/oscillation nightmare.
    No time available to fully strip it and have all chassis parts blasted and galvanized (or at least *properly* phosphatized) so I had to grind a spot on each part and solder a grounding wire which electrically joined all.
    Steve Conner, cminor9 and Wes like this.

  27. #27
    Supporting Member Chuck H's Avatar
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    Damn JM. That's very cool. And practical, real world evidence. Not very "guru" like of you to offer practical, real world evidence.
    "I've heard magic defined as "a technology you don't understand". By that aphorism, the folks in this forum are practicing wizards, able to summon AND control the lightning demon, and make charms to allow others to use the demon in certain ways." R.G.

    "...less ear-friendly but handy for jazz." Leo_Gnardo

  28. #28
    Member broken flyer's Avatar
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    Quote Originally Posted by defaced View Post
    Damn, this is like talking to me 15 years ago, but instead of building amps, I was building bike ramps and grind rails. Our school was the same way, we had an old Lincoln in the corner that was never used for class, but if you knew you to hook it up and grind a tungsten, you could use it. I read two books cover to cover before I struck my first TIG arc, I think I was able to get both of them from the local library:

    Welder's Handbook: A Complete Guide to MIG, TIG, Arc & Oxyacetylene Welding by Richard Finch Amazon.com: Welder's Handbook: A Complete Guide to MIG, TIG, Arc & Oxyacetylene Welding (0075478012640): Richard Finch: Books
    Gas Tungsten Arc Welding by William H. Minnick (I have the older blue/purple covered edition, so you may find a copy that isn't yellow, but it's still the same book, just an earlier edition) Amazon.com: Gas Tungsten Arc Welding Handbook (9781590705810): William H. Minnick: Books

    Most TIG welders will have a big honkin switch on the front of them (if they're old transformer/rectifier styles, new ones are all different, but usually it's a small push button) that change from DC negative, to DC positive, to AC (if it has it). Sometimes there won't be a DC +/- switch, you have to swap the leads on the machine.

    If you can gas weld, you've got the hardest part of TIG welding already worked out, and that's feeding wire with your hand (it's actually easier when you TIG weld because you can use thinner gloves). Since TIG uses a foot pedal, usually what guys do is set the current on the machine for the max they want, and since the foot pedal is like a volume control, they just smash the pedal to the floor and give the arc the current they set on the machine. That takes the pedal out of learning to TIG weld, but I think you'll find it pretty easy to get the hang of.

    And yes, I used to urethane all of my welding projects because I hated painting. The wood shop had a nice spray booth, but you could only shoot their clear urethane in there, so that's what I did. For a clear coat these days, I use Rustoleum clear that I pick up at Lowe's. As long as you cover up the steel somehow, you'll prevent it from rusting.
    Alright, i think i'll need to look around the shop a bit and see if i can find a scrap of 16 gauge steel, then if my punchs can handle it i'll just bend it up out of 16 gauge steel, wire feed the corners, paint the face, and then do a clear coat over the whole deal. I'm still gonna give aluminum welding a try before i write off as it does have nice shielding properties as well as being easy to put holes in. Thanks for all the help...
    I'm sure i'll be back on here with more questions before too long.

  29. #29
    Old Timer defaced's Avatar
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    You're welcome. Keep the questions coming.
    -Mike

  30. #30
    Old Timer J M Fahey's Avatar
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    FWIW, this is an actual, commercial drawing of a 5F1 tube amp chassis, produced in series.
    Steel 18Ga , C shaped, turned into a box by (resistance) spot welded box ends.

    When producing professionally and in quantity, with the proper presses and dies, steel is cheapest, easy to spot weld, and galvanizing costs cents.
    No expensive Tig/Mig welding, although the choice aluminum solution is riveting (just watch the zillion airplanes flowing all over the world .... which AFAIK do not "melt" in the air either).
    For 1 offs, however, itīs not so anymore, specially for the home builder.

    To see real size, right click and choose "view image".

  31. #31
    Old Timer defaced's Avatar
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    No expensive Tig/Mig welding, although the choice aluminum solution is riveting (just watch the zillion airplanes flowing all over the world .... which AFAIK do not "melt" in the air either).
    So NASA should have riveted those aluminum fuel tanks together?
    -Mike

  32. #32
    Old Timer soundguruman's Avatar
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    Quote Originally Posted by defaced View Post
    So NASA should have riveted those aluminum fuel tanks together?
    One of the materials used by NASA to assemble the space shuttle boosters was duct tape.
    No, I am not making this up, absolutely true.

  33. #33
    Old Timer J M Fahey's Avatar
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    I think those tanks were made out of very thin stainless steel, so thin that they keep their shape only because of internal pressure.
    I don't feel comfortable that close to the edge of the precipice.

  34. #34
    Old Timer defaced's Avatar
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    Nope. They are aluminum-lithium alloys friction stir welded together: http://www.nasa.gov/centers/marshall...n_friction.pdf. For a more applicable example, look at Hammond's 1444 series amp chassis: spot welded. Ever looked at an aluminum trailer, MIG welded. And lastly, look at an aluminum bike frame, TIG welded. Aluminum is quite weldable, and is done for reasons revolving around the design and application of the end product, same with rivets. Saying one is better than the other is like saying steel is better than aluminum or vice-versa (especially in broad categories like "steel" or "aluminum", neither of which are specific enough to have a real engineering design conversation around).
    -Mike

  35. #35
    Old Timer J M Fahey's Avatar
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    Cool !!
    Your data is fresher than mine
    Loved the Hammond chassis too.

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