help with chassis

[uneumann]

I'm working on a new project to build a 5F6a replacement chassis - but with more features and lighter weight. I'm well along on the circuits but the chassis is a problem... My design is below. I'm not a good metal worker and I don't have the right tools to do this so I'm looking for a fab service and I got a quote for over $300 for a first unit prototype. Quantities of 10 drop the price to around $60. While I think these costs are reasonable - perhaps someone out there knows someone... or is interested in teaming on this project... whatever. I'd appreciate pointers from people that do more metal fab than I do.

Also - this isn't just a personal favor - I'm making the entire design public so anyone can reproduce it or mod it or "borrow" ideas from it. There are too many details to post them all here - so if you're interested check it out https://sites.google.com/site/string...m-lite-project
This thread is perfect for comments/suggestions.

The chassis drawing is below.



The material is aluminum. I'm open to thickness - I've seen many suggestions for 0.08" thickness, but since there are no heavy components, that may be overkill. The heaviest component is a small filament transformer (~0.5 Lb). This should be a light chassis that can drop into any 5F6A cab.

[J M Fahey]

2mm is not overkill, Iīve used it for decades, now down to 1.5 mm but reinforced where needed.

The point is that you seem to be using a "C" shaped chassis without reinforcements, hanging from one edge by a couple 3/16" bolts (like original Bassman).

Nothing will break but that shape and mounting is flexible, suggest you either add sides closing the C into a tray or at least a couple aluminum strips or a piece of tube, even 1/8" is strong enough because itīs only subject to compression/expansion and itīs rigid on that behalf.

Traditional Fender chassis are made of iron which can easily be spot resistance welded, while aluminum can not (at least to us outside NASA) so reinforcements must be riveted or bolted (unless you want to splurge and use TIG/MIG welding).

Suggest you order extra front panels in thin aluminum together with the chassis, wonīt cost much because their holes match the chassis top so the programming and setup are already paid for, and give you the flexibility of anodizing/brushing/painting/blasting/silkscreening independent from the main chassis , which being aluminum migh even stay unfinished.

[loudthud]

Mini toggle switches (if that's what the four 1/4 inch holes are for) can easily be broken when they are on the back edge of the front panel. They are more protected if they are above the center line. The hole for the mains cord should be a double D to prevent the strain relief from twisting. (Why are there three holes?) You might consider an IEC inlet connector. Most chassis you see use a round hole but the one I got from Hoffman has the double D. Thank you Doug!

[uneumann]

Thanks Juan, LT - great suggestions - several point I had not thought of.
As a result, the chassis will be closed/reinforced on ends. Front panels strips are great idea. Power inlet will get redo - either DD or IEC. Yes - mini togs are exposed - so I'm using small-bat (0.256) versions from NKK. Moving them below PCB obscures both the switches and their connections, which I want to avoid. These tuck in below knob level, but are still big enough to see and manipulate easily (IMO).

Again - thanks for the thoughtful suggestions.

Vendor pointers (anyone in LA?) would also be helpful. I'm also open to barter ... maybe a PCB set for a proto chassis?

[J M Fahey]

If you want to pre-pre-try the idea, which is always advisable on a new design and you donīt intend to *sell* that prototype (although I never could keep one, always *someone* appears who wants it "as-is", with toolmarks, scratched and unfinished) , you can simply buy a piece of 2mm aluminum, have it cut and bent into a C shape, no reinforcements or anything else, and you drill all holes yourself.
Even with a hand drill if you donīt have a bench type one.
"Round holes are easy" [tm] and drills are inexpensive.

Ok, holes wonīt be *perfectly* aligned because drill tips always "dance" a little, although predrilling with a thin one serves as a guide for the definitive one.

Also holes are not perfectly round but slightly triangular (unless you have a good firm bench drill *and* you firmly clamp the chassis down) , itīs a problem typical of thin metal pieces, also edges will be rised (on both sides of the sheet) because aluminum is soft and flows under pressure, but being soft also means that edges can be cut flat and even beveled if you wish with a single 13mm drill mounted on a round wooden file handle (so as not to damage your hands).

In a nutshell, you will be able to home make a perfectly adequate chassis where you will be able to build your first "proof of concept" design, for less than $50 .

I have done that for decades, I bet most experimenters have done something similar one time or another, for the prototype you may even just skip the D or PC type connector and make do with a simple round hole, a rubber grommet and a plain AC cable through it with a knot inside ... shades of Leo Fender Prototypes

Labels written in fine tipped Sharpie are the finishing touch

I BET after the prototype is built and tested, even some YT video is uploaded, you WILL change something , but if you are not fussy (first prototype ) you can add new holes and/or not use others.

Only after being certain you can order that 10 chassis batch which at $60 each (factory cost) are REAL inexpensive.

You can cut the noval hole sockets with a Greenlee type punch, a stepped drill (somewhat expensive but VERY useful and finish is perfect because the next larger step deburrs the one you actually need) or a "cup saw" which leaves very messy hole edges BUT can be had in any large size, up to 2" or beyond.

IF you can get an OLD (think 40īs to 60īs) ARRL (radio amateurs) handbook, they have lots of data and ideas for home making complex chassis, those hardened amateurs built everything from the ground up.

[uneumann]

If you want to pre-pre-try the idea, which is always advisable on a new design and you donīt intend to *sell* that prototype (although I never could keep one, always *someone* appears who wants it "as-is", with toolmarks, scratched and unfinished) , you can simply buy a piece of 2mm aluminum, have it cut and bent into a C shape, no reinforcements or anything else, and you drill all holes yourself.
Even with a hand drill if you donīt have a bench type one.

Sure - I've done chassis by hand before. The chassis layout and PCB circuits are pretty solid at this stage, so a hand-made pre-pre-proto isn't appropriate since the risk of surprises is low. The point of this project is to make something reproducible. So I'm pursuing a CNC fab process - which is something I've never done before. I'm learning about options and decisions that are unique to this process. I'm "debugging" the CNC/fab process.

I probably didn't clearly relate my goal... it's to create an amp design that is documented to the degree that anyone can download the info about the circuits, chassis, parts, etc... everything needed to order and build a version. I'm not selling anything, but I'm posting the info needed to order everything and build it. I see it as an "info kit" and an alternative to the many vintage amp kits with heavy PT and OT transformers. As an "open design" it may also lead to versions or uses I can't yet imagine.

[catalin gramada]

no worries about thickness. Weld the corners, it is a huge difference

[dchang0]

If you are going to make this in small runs, have you considered getting/renting your own mini CNC mill? The chassis may be larger than the work area, but you could move the chassis a few times to get around that. Precision is not necessary, so the moves will be quick, especially if you build jigs to speed up the alignment. Aluminum is no big deal for desktop CNC mills.

[J M Fahey]

FWIW a close friend used to make custom Studio stuff, specially microphone preamps and channel strips, and bought a room door sized CNC (leter he found it was overkill and took more space than he wanted, so think ahead) .
he designed them in some special software I never learnt, and cut everything from extruded aluminum strips of various shapes.
Then he found a killer anodizing guy who had the best black (the most difficult colour) we had ever seen.
Results were stunning.

[dchang0]

If this handheld CNC "mill" (really, it's a smart table router) ever makes it to market, it will be a HUGE boon to amp builders.

You would only need this and a sheet metal brake and maybe a TIG welder to build your own chassis quickly.

https://www.youtube.com/watch?v=Xo0C...ature=youtu.be

[SoulFetish]

I'm in a similar situation with the amp I'm working on. At some point I plan to outsource my chassis to be laser cut and silk-screened, along with my cabs.
I figure, I like the artistry of the entire build process and am confident in my ability to do fine woodworking. I assumed that more I could build and fabricate myself, the more money I could save. So I talked my father into what a great idea it would be to split the cost of a beautiful new Japanese dovetail saw and a great dovetail guide for his woodshop (he's great. trying to convince him to invest in good tools is like the easiest conversations I've ever had in my life). But, at some point I realized that I want to spend my time designing circuits, trouble shooting, and building in the chassis. Spending the time I would need on the cabinetry, when I want to go into production seemed inefficient. In any case, I'm leaning in the same direction for my chassis as well. Having said that, I'm in total agreement with Juan with regard to the prototype build. With the proper few tools (which he mentions), and a well designed layout, you can get pretty close to precision. I would add that perhaps the most valuable tool I've used in the fabrication process is a center punch. I've been documenting the process so far and you can see some of the steps and results...

I started with mounting the layout cut from two 8.5X11 (I had to adjust and separate one side of the layout where they jointed to compensate for the chassis not being dead square. I didn't make the chassis )



scoring the center holes


center punching


pilot holes drilled and matched to double check


greenlee punch 13/16"

tube sockets done.

I was not looking forward to the IEC hole at all, but I came up with a technique which made such quick work of it using a drill bit, step drill, and file! (I remeasured the center punches to double check against the datasheet and realized I made an error in the drawing and re-punched the back panel. That's the row of marks just above the ones I drilled)




Oh, one thing I wanted to mention was in addition to what Juan said about using a step drill. I find that the while the drill de-burrs the top of the whole, the bottom often needs deburring. Supporting the chassis with wood to drill into helps a lot. But, a good de-burring tool makes for some nice finish work and easy install of panel mounted components.

[dchang0]

Would a square chassis punch have worked for your IEC hole? I have seen various sizes of square chassis/knockout punch--hopefully the size you need is one they sell.

I used a titanium-coated step drill for the 5F1 chromed steel chassis I added a one-tube reverb to. The step drill was worn dull by the steel chassis. It would have worked fine for aluminum. I wonder if the bit could be re-sharpened... Had I known I would ruin the step drill bit I would have spent the money on a proper chassis punch.

[SoulFetish]

Would a square chassis punch have worked for your IEC hole? I have seen various sizes of square chassis/knockout punch--hopefully the size you need is one they sell.

I used a titanium-coated step drill for the 5F1 chromed steel chassis I added a one-tube reverb to. The step drill was worn dull by the steel chassis. It would have worked fine for aluminum. I wonder if the bit could be re-sharpened... Had I known I would ruin the step drill bit I would have spent the money on a proper chassis punch.

If Greenlee had one close to the size hole I use for the IEC I use, I would probably drop the $400. But I checked out every rectangular punch dimensions and none of them get me as close as my cut. But if you come across one close to 28mmX32mm, let me know because I'll be in the market for one till I find it. The encouraging thing is everything is lining up within tight tolerances to how I designed the layout, which is a little surprising. These were a quick mockup to see how the actual parts would fit and make sure all is as it should be.

[hylaphone]

I've been scouring for a fused IEC sized punch as well.
There is one available for the standard, non-fused size. Requires a hydraulic punch.
Punch & Die for Control Panel : auberins.com, Temperature control solutions for home and industry

[J M Fahey]

Hey, itīs looking GOOD and very PRO