Lets build a chassis!

Discussion in 'Shock Brother's DIY Amps' started by Nickfl, Sep 10, 2019 at 10:43 PM.

  1. Nickfl

    Nickfl Tele-Afflicted

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    As I've gotten further out into the wilderness of this amp building hobby I find myself moving towards builds that are less and less clones and more one off's loosely inspired by classic circuits, if they have any reference to vintage amps at all. For this reason I've ended up making my own chassis from scratch on my last couple of builds and as much as I don't especially enjoy working with metal, it is satisfying to be able to just make exactly what you need instead of trying to find a way to make a commonly available chassis work for something totally different.

    I had been using a cheap Harbor Freight sheet metal brake to bend with, while keeping an eye on craigslist for a better tool for the job. Last week I finally came across a good deal on a Shop Fox box and pan brake and jumped on it.

    IMG_20190910_223636.jpg

    Its an entry level unit, but they are still way too expensive for me to justify buying one at the new price, but the guy selling it only wanted about 30% of what they cost new and that fit my budget and felt justifiable for my limited needs.

    Having a new tool in my garage inspired me to finally get started making the chassis for my next project and I thought I would try to document the process as best I could for anyone interested. As I said, I am not much of a metal worker, so if nothing else this may inspire someone when they see that a serviceable custom chassis can be made with some basic tools and minimal skill!
     
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  2. Phrygian77

    Phrygian77 Tele-Afflicted

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    Well, I got an undrilled/punched chassis for Trainwreck build, Express or Rocket, haven't decided. That's as far I'm going to go. I don't have a brake, or other sheet metal tools like that.
     
  3. Phrygian77

    Phrygian77 Tele-Afflicted

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    Table saw and drill press are about all I have room for in the garage
     
  4. Nickfl

    Nickfl Tele-Afflicted

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    Step one is to choose the right material. I prefer aluminum as it is much easier to cut and drill than steel and still plenty strong as long as you get a reasonable thickness. An important lesson I learned on my first chassis is that aluminum isn't all the same, there are several different alloys commonly available and you need to choose the correct one. I used 6061 on my first build and while it cuts and drill like a dream it is extremely difficult to bend. After that I did a little research and settled on 5052, which mills well enough and is much better for bending. For this chassis I am using 0.062" 5052 sheet I got from Mcmaster Carr.

    The first thing to do is layout the unfolded chassis shape on your sheet and then cut it out. One one of the many nice things about using aluminum is that you can cut it with just about any power tool. It is very easy to cut on a table saw (it is loud though) but I am using a jigsaw because I don't want to get metal shavings all over my wood working area. You can make a nice, straight cut with the jigsaw by clamping a straight edge to the sheet metal to guide your cut.

    IMG_20190906_181433.jpg

    Once I cut out a square the size of the unfolded chassis, I then mark it where it will eventually be folded and cut out the waste areas between what will become the vertical and horizontal sides of the box.

    IMG_20190906_183552.jpg
     
  5. Nickfl

    Nickfl Tele-Afflicted

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    Thats really all you need other than some sort of metal brake. You don't even need the table saw but it is good for cutting aluminum. The drill press is really the most helpful tool in the process and you could do most of this with that and a $30 sheet metal brake from Harbor Freight, which is how I did my last two!
     
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  6. Phrygian77

    Phrygian77 Tele-Afflicted

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    But, bending metal takes some art. The bend radiuses (or is it radi lol), don't always do what you expect.
     
  7. Phrygian77

    Phrygian77 Tele-Afflicted

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    I use the table saw for cutting board material. I hate it though. Looking for a better solution like a small tile saw.
     
  8. aerhed

    aerhed Friend of Leo's

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    A big thing with alloy sheet is it's hardness state. Aluminums come in many different levels of hardness from type O, which you can bend with your fingers to levels that will snap when you look at them. You can buy aluminum you need to keep in the freezer until bending. It will age and air harden afterwards.
     
  9. Nickfl

    Nickfl Tele-Afflicted

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    Next I layout all of my component holes. Long before I start any of the physical work, I do a full layout in DIYLC. I find it is worth the extra effort to do these to scale, even going as far as making sure the electrolytic caps and big resistors are the correct size so I don't have any surprises down the line. I will then measure my chassis hole locations based on that and lay them out on the metal using two adjustable carpenters squares like so:

    IMG_20190906_184544.jpg

    I have found this to give me good accuracy and it helps to keep the holes in a straight line. I use a spring loaded center punch to mark the drill holes and then take it over to the drill press to drill pilot holes.

    IMG_20190906_192716.jpg

    It is a good idea to start with a relatively small drill size and then work your way up to the actual hole size from there. I use a standard spiral bit to drill the pilot holes and then enlarge them with a step bit. It is also important to make sure the drill press is set to its slowest speed. When you are drilling metal, the bit should always be making shavings not just spinning and getting hot, drill bits started lasting a lot longer once I figured that out!

    IMG_20190907_163554.jpg

    Another game changer was learning about this little guy, the deburring tool. One of the many things I learned here at TDPRI, specifically in this thread posted by @RollingBender It is so much better than using a dremel to grind the holes smooth!

    The step bit works well for holes up to the size needed for things like jacks and power switches, but tube sockets are best done with a punch. If you like having the correct tool for the job, greenlee makes radio chassis punches in the exact sizes for tube sockets, but they are $$$. I'm sure I will eventually get some, but for now I've been using a set of conduit punches from Harbor Freight. They aren't exactly the right sizes, but they are close enough if you are using top mounted sockets as they will cover the gap and you won't see it from outside the finished chassis.

    IMG_20190907_170008.jpg
     
  10. King Fan

    King Fan Friend of Leo's Ad Free Member

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    Super impressive, Nick. Also fun to follow along. Thanks.

    It sounds like you're all over the CL / eBay angle, but I've heard that Greenlee punches sometimes come up for sale at reasonable prices.
     
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  11. sds1

    sds1 Tele-Afflicted

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  12. Robear

    Robear TDPRI Member Ad Free Member

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    Gonna watch this thread.
     
  13. Nickfl

    Nickfl Tele-Afflicted

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    Now that I've got all the control panel and tube sockets drilled, its time to do the transformers. But first, don't want to forget the mounting hardware holes for the tube sockets. First I mark a 45 degree angle across all the sockets using the adjustable carpenter's square again.

    IMG_20190907_172053.jpg

    I then mark the holes themselves using a tube socket as a template and drill them. Unfortunately these holes are so small that they are the only ones I can't use the deburring tool for and they just have to be ground smooth.

    Next I'll do the power transformer, which is still kind of a struggle for me. If your transformer manufacturer provided a drill template this is easy, but mine didn't so I just have to measure carefully. First I'll drill the mounting holes and make sure they line up.

    IMG_20190907_180548.jpg

    So far so good, now to cut the hole for the transformer bell. I'll lay it out on the sheet, then drill holes at each corner large enough for the jigsaw blade and carefully cut it out.

    IMG_20190907_180554 (1).jpg

    Which went ok... in the end I had to enlarge one of the bolt holes to make it line up properly, but this won't be visible once the transformer is installed.

    Now all that is left is to drill the mounting holes for any other transformers, in this case the OT and reverb transformer. These are both much easier than the PT because they are mounted upright and can therefore be used as templates. Lastly I'll drill a couple of holes for the wire pass through grommets (also easy because their location is more or less arbitrary) and we are done drilling!

    IMG_20190908_134427.jpg

    The only holes missing at this point are the ones for the circuit board mounting standoffs, which I won't do yet because I need to make my circuit board first.
     
  14. Saxonbowman

    Saxonbowman TDPRI Member

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    This is very interesting to follow along. Thanks for posting it!

    You've probably thought of this but I suppose for the transformers you could always make a cardboard template before you cut the metal.
     
  15. Nickfl

    Nickfl Tele-Afflicted

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    Now its time to actually use the tool that inspired me to start working on this and do some bending!

    I started with the bend closest to the long edges which is the lip on the inside of the chassis. Next I did the bends between the back and the top and bottom. All went well up to this point, but I didn't get many pictures of the process because I got distracted when things got difficult with the sides of the chassis. Unfortunately my box brake is just a little too shallow to properly bend the sides of this chassis, which is 2.75" deep. I think I would have had no trouble with a blackface or marshall style chassis, but a tweed style like this required me to improvise.

    IMG_20190908_140322.jpg

    I ended up bending the sides as far as I could (about half way) and then finishing the bend with a wood block and hammer. These bends aren't nearly as nice as the others, but they'll do for a first try. I later read a tip for this kind of situation saying you should bend the sides first, then partially unbend them so you can to the other bends, which will allow you to manually bend them with a better corner (if that makes any sense). I'll give that a try next time.

    And here we are with something that looks surprisingly like an amp chassis :D

    IMG_20190908_144030.jpg

    And the moment of truth where we see how it fits the cabinet (which I made a year ago, originally for a different build that didn't ever happen).

    IMG_20190908_144243.jpg

    Looks like it will work. I've got to make my board so I can drill standoff holes and then I'll be ready to paint the chassis.
     
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  16. Nickfl

    Nickfl Tele-Afflicted

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    Yeah, thats actually what I did last time I had to do one like this. This time I was too impatient and thought I'd just measure and lay it out directly... lesson learned.
     
  17. Paul-T

    Paul-T Tele-Meister

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    this is fantastic. Many thanks. At least two vital bits of advice for me when I make my first simple chassis in the next month or two.
     
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  18. guitarbuilder

    guitarbuilder Telefied Silver Supporter

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    I used to work with a metal shop teacher and when our program changed in the mid 80's and he retired, I inherited his 36" shear, 36" Pexto brake and his surplus sheet metal. I used it for almost 30 more years. It was USA made equipment probably from the '50's. I added a Grizzly Punch and a spot welder to the arsenal and we used to make galvanized tool boxes for a while and various sheet metal parts for other manufacturing activities. I'm sure it was sold at auction when I left for next to nothing. This is a cool thread.
     
  19. LudwigvonBirk

    LudwigvonBirk Tele-Holic

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    Nice job NickFl!

    Not counting initial tool acquisition and setup: ~How many total hours did this chassis take you to complete?
     
  20. ArcticWhite

    ArcticWhite Tele-Meister

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    You probably already know this Nick, but always put a little machine oil on your bits before drilling metal. Makes the bits cut easier, and last 3 times as long.
     
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