While waiting for appropriate temperatures to paint and apply oil finishes, I’ve been working on a simple preamp project. It’s only a handful of parts and to avoid complications with finishing a handmade chassis, I decided to use a preformed aluminum project box I had sitting on my shelf. I quickly regretted that decision.
I’ve gotten used to working with hand selected materials. For the metal plates in amplifiers I typically use an alloy of aluminum common in the aerospace industry, 6061-T6 in 0.080" (≈2mm) thickness. This alloy is strong yet highly machinable and tooling generally leaves a nice smooth finish. And because of the manner in which I build most of my wood chassis, I am normally working with flat sheets of aluminum and sometimes small angle stock in projects like the 6EM7 Vertical Amp or the Zebrawood amp.
The pre-formed project box I chose to use is one from a windfall I stumbled into about a decade ago. I have a sizable stack of these boxes. These project boxes are ubiquitous in the electronics industry; generally folded from relatively thin aluminum or steel and spot welded at the corners. The ones I have are made by Bud Industries, but there are numerous other manufacturers. They all look mostly the same. Here are a couple from my parts closet.
These boxes are formed from 0.040" aluminum. I don’t know what alloy it is but it’s kind of gummy and doesn’t take a finish particularly well.
After marking up the box I retired to my shop to center punch holes and do some drilling. This is when the problems started. The tooling was chattering and not cutting particularly well. Even when using my typical cutting fluid Relton A-9. The cutters were leaving nasty burrs on the back side of the holes and trying to drift while being drilled. Getting these burrs off the insides of holes inside the box was a particular difficult chore. In addition, due to the soft and thin material used, the box would distort when I started to drill so each hole had to be drilled very slowly and with a very light touch. I couldn’t believe that such a simple task could be giving me so much trouble.
I finally prevailed in getting the chassis drilled but it did take an exceptional amount of fussing with details to make things work out alright. Here’s how it turned out.
The plate in front of the chassis is a bottom cover I made for the project box out of a piece of my 6061-T6 80mil aluminum. It took surprisingly little time after fussing with the chassis all morning. I’ve taken to using the cast aluminum boxes like the BUD CU-476 for small projects. Compared to the sheet metal ones, these cast boxes are a joy with which to work.
So my question is how do people like using boxes like these sheet metal project boxes? I know that Hammond makes these types of boxes out of aluminum and of steel but I’ve never used one of theirs. Are there some on the market which are better than others?
I know that my recommendation is to build your own chassis if possible. Preferably out of the best quality wood and metal you can afford. Given the cost of building even simple tube projects, having a nice chassis doesn’t seem like too much to ask. What’s your opinion?