Wednesday, August 2, 2017

Discreet Transistor Keyer Part 4 - Building the "scrap metal" enclosure.

In my last post, I mentioned Master Homebrewer Pete, N6QW's recent blog showing how he builds beautiful enclosures using an inexpensive bending brake.  Pete, a true craftsman, did a marvelous job, as any craftsman who takes pride in his work would.

Now, I'm going to show you the other side - how to quickly bend up a simple enclosure from a piece of scrap 22 ga. aluminum.  Because for some projects, simply being good enough is good enough!

I started with a couple of scrap "rails" that I had left over from another project and the keyer's circuit board:
Laying the bits on the bench, I took a couple of measurements and determined that the box would be about 4 1/2 inches square by 1 1/2 inches high.  The easiest enclosure to make (in my opinion) is the simple "clam shell", where you have  top and bottom panels that slip over one another to form a box.  Since I already had the rails for the front and rear, this one will be easy because I only need two bends in each panel. 

For the bottom, I laid out the dimensions on the scrap aluminum sheet.  Since the dimensions are 4 1/2" square and I'll need about a 1/2" "lip" on the left and right sides, I cut the piece to 4 1/2 x 5 1/2" using a pair of shears.

In the last picture, you can see the lines drawn on the soon-to-be bottom panel that show where the bends will be, um, bent.  Now, it's off the the "back room" to do the bending!
Lined up and clamped in the brake.  For a small bit like this, a single vise-grip is enough to hold it in place.  I use multiple C-clamps when working with larger pieces.

One side bent - square bend in seconds, try doing that the way the old handbooks tell you to. 

And repeat for the other side...

The top is formed the same way, except that I left a full-height (1 1/2") "overhang" on each side instead of the 1/2" used on the bottom panel.
The components, ready for assembly.

When I'm in the mood, I've got a jig that I made to drill mounting holes in the corner of PCB with some degree of precision.  This isn't one of those times, so I laid the board where I wanted it to go, drilled the hole for one corner and fastened it with a screw and nut.
The single screw/nut hold the board in place while I drill the other three, and then all four corners get fastened.

Next, I fastened the front and rear panels to the bottom with pop-rivets.  Unfortunately, I didn't capture the excitement photographically, but trust me, it happened.

Now for the only "exotic" piece of hardware in this entire project: Rivnuts! 
Fastening the top of the enclosure to the box means that I'm not going to be able to use screws with nuts, and if I use rivets, then I'll invariably have to drill them out to fix something.  I could use sheet-metal screws, but they eventually get sloppy after being undone-redone a few times.  Rivnuts are cool; they're threaded inserts that attach like a rivet - the tool looks like a pop-rivet tool that, rather than having a hole for the rivet "lead", has a threaded stud.  Installation is a snap - drill the hole (for #6-32 inserts, drill a 9/16" hole), screw the Rivnut onto the tool, insert, squeeze the handle and bingo!

And that's it.  The finished product is certainly "good enough"; with a little body-work (filing the edges smooth and massaging out any dents) and paint, nobody will know that it was whipped together in about 45 minutes from a piece of scrap.


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