The first step in building the power supply was to get a box. According to the specs, it needed to be (9" x 9" x 3") or larger, and at least the bottom needed to be aluminum for heatsinking purposes. Turns out, while smaller aluminum boxes aren't too hard to come by, most project boxes of any size are plastic these days. Luckily, after asking around, it turned out that our Shop Coordinator Gary had some fully aluminum boxes around, and they were big enough for the project.

Unfortunately, they were a lot bigger too! The height left plenty of clearance, the width was about a foot, and the depth was even larger. I could have used one as-is and made a functional power supply, but a supply that huge would have been clumsy and unwieldy, especially considering that my electronics workspace is a converted closet. So instead, I opted to modify the box, relishing the chance to get some more machine shop experience.

The two halves of the box held together after cutting. They match pretty well, particularly along the sides. On Gary's advice, I decided to cut the back panel off, then slice off enough material to make the box a reasonable size. Since the width is longer than 9", I can afford to make the depth significantly shorter than 9", saving on desk space. To cut the box, I used a bandsaw, stacking spare planks of wood next to the guide until the thickness was about right. Afterwards, I smoothed the surfaces with a metal file. Since the cuts were guided, the two pieces fit together quite well, especially along the sides.

The box, prior to being assembled, along with the little brackets I made to rivet it together I also made some brackets out of a bar of scrap aluminum stock. I measured 8 one-inch intervals and cut them on the bandsaw. (Since the saw blade removes some material, they ended up being a little shorter than an inch apiece, but that doesn't matter within the accuracy I needed them for.) Then I smoothed the edges a bit on the sander, and stacked them all together. Using the drill press, I made two holes in each for the rivets to go through, so they were all the same length.

Here's where I learned a valuable shop lesson: never assume that the idiot who last used the drill bit put it back in the right place! I took my newly-created brackets upstairs to Gary's shop, and tried putting a rivet through one, only to have it get stuck on the obviously-too-small hole. Measuring with the calipers (as I should have done in the first place) confirmed that the bit was smaller than the slot where it was put away. I had to restack the brackets and drill the holes again. (When trying to line them up again, I noticed that the inside of an old pen could just barely be squeezed through the holes. I clipped it off at the edges and just drilled right through the plastic.)

Now that the brackets had big enough holes, it was time to put the box together! Well, almost. Turns out, it's a better idea to make any back-panel holes before assembling, since the back panel is more stable alone than together (due to its low depth). As for the rest of the box, having the back panel riveted on will add stability, so any other holes should be made after it's all assembled.

Shaping the hole for the power cord receptacle using the sheet metal nibbler The only hole the back panel needed was for the power cord receptacle. It's somewhat irregularly shaped, so a regular drill bit simply won't do here. What's needed is a special tool for sheet metal work called a 'sheet metal nibbler'. It chomps off small, rectangular bits of sheet metal. After making an initial hole with a drill bit, I could just nibble out the rest of the shape. After measuring and drawing the approximate shape, I went to work on it.

The power cord receptacle inside the newly-nibbled hole: it fits! As we can see from the front view, the lip covers up any parts where the hole was wider than it 'needed' to be. Finally, I had enough nibbled out so that the receptacle could fit inside. From the back view, you can see some areas where the hole is too big. However, the front view shows that the lip which runs around the receptacle is more than enough to cover these gaps. In order to make the holes in the case to screw it in, I just drilled right through the holes in the lip of the receptacle while it was wedged in the newly nibbled hole.

This is the way to clamp the workpiece to the table... if you're an idiot. Putting the clamp directly on the back -- on the visible side, no less! -- will leave a distinct ugly impression in the soft aluminum. A much better way to clamp the workpiece. The wood spreads out the force of the clamp, putting much less pressure on the aluminum surface. The visible face is also better protected. Now I was ready to put the rivets in the back piece. I measured four equally spaced spots along the bottom, and two on each side, and clamped my piece to the bench. Unfortunately, my lack of experience showed, and I put the clamp directly on the outer face of the back piece. This puts an enormous pressure on that small area and will leave an ugly indentation! I soon fixed it by turning it upside-down, and putting the wood block between the clamp and the workpiece, spreading out the force so as to put less pressure on the face.

Riveting the brackets to the newly-drilled holes, in the clamped workpiece. After grooving each marked spot, by placing an awl at the point and tapping it with a hammer, I drilled each of the holes around the perimeter, using a countersink to deburr by hand. Now I was ready to start riveting the brackets in place. Once each rivet breaks off in the bracket, it holds it steadily in place so that it won't easily rotate.

All the brackets are now in place for the back of the box! Eventually, all 8 brackets were in place around the perimeter, and it was time to place the back of the box in its proper place and start attaching the rivets. We could have drilled all 8 holes right away; however, aluminum tends to move and bend a fair bit. The better strategy was to drill a hole, deburr it, and rivet that hole straight away before going to the next one.

An outside view of the newly assembled box. Looks pretty good from this angle! The inside of the box: maybe a little rough-looking, but solidly put together. After all 8 holes were drilled and riveted in this way, the box was complete! It has the hole for the power cord receptacle in the back, but all the other holes still have to be made (that's the next step). I'm quite pleased with how it ended up looking, particularly from the outside. And the size is quite convenient too -- I'd much rather have it be 'overwide' compared to the specs, than to have a full 9 inches of depth!

A sneak preview of how a lot of the major components are likely to end up looking. Finally, I stuck most of the major components near their final spots to see how the layout is likely to look. Shown are the rubber feet (four corners), the power transformers (top left), the bridge rectifier (below the transformers), the capacitors (to the right of the rectifier), and the circuitboard (right side). I haven't soldered together the circuitboard yet, and I obviously didn't take the power transistors out of their protective bags -- why risk a static discharge for a photo op? I also didn't show the potentiometers/banana jacks for the front panel.

Now it's time to measure and drill the holes to begin laying out the components.