This is a practice box, so it's not very nice-looking. You can build it to get a feel for working with various sheet metal tools: metal shears, box brakes, pop-rivets, and so on. We're not going to touch upon bend radii or bend allowances, but these are important subjects if you want to get into anything more precise.
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Step 1: Tools and Materials
We will make the box out of 0.032" (1/32") aluminum sheet metal. You'll want to get a 12" x 12" sheet at least. Here I'm using 6061-T6 aluminum. Feel free to experiment with different alloys.
You will also need:
* Left and right sheet metal shears
* A spring-loaded punch
* Cleco pliers and at least 18 cleco fasteners, 3/32" diameter
* At least 24 steel pop rivets, 3/32" diameter, 0.225" length (for a grip range of 0.032 - 0.125" and a hole size of 0.097" - 0.100")
* An air-powered or manual pop riveter
* A thin permanent marker
* A small file
* A square with ruler
* A metal shear
* A box brake
* Two long-nose locking pliers
* At least a 2 3/4" length of 1" wide aluminum hinge, without holes
* A drill
* A 3/32" drill bit
* A 1/8" drill bit
* A #40 drill bit
* A drill bit somewhat larger than 1/8", it doesn't matter as long as it's larger. 1/4" would work.
* Preferably, calipers
* A vertical bandsaw or a hacksaw
Step 2: Making the Sides (part 1)
We start the box by making its sides. The sides will be 3" x 3", but we add 1/2" tabs on three sides. So, mark out two 4" x 3 1/2" sections of sheet metal, and cut it in the metal shear. It is easier to cut off a 4" x 12" strip (if you have a 12" x 12" sheet) first, then cut two 3 1/2" pieces from that strip.
With the marker, mark off a line 1/2" away from each short edge, and one line 1/2" away from one long edge. These are your bend lines.
Where the lines intersect, use the spring-loaded metal punch to put dimples in the metal. This is where you will drill, and the dimple helps to prevent the bit from wandering around.
Use a 1/8" drill to drill the two holes.
Use a larger drill bit, and gently twirl it in each hole once or twice, not pressing hard. This will deburr the holes.
Step 3: Making the Sides (part 2)
Next, use the left and right metal shears to cut out the small squares at the corners. These tools have a bottom blade and a top blade. The bottom blade supports the material you want to keep, because the cutting action will bend the metal on the opposite side. Thus, you'll need to use both left and right shears to cut away the little squares.
Clip off a tiny bit of each corner.
File all the edges so that when you rub your finger on them, you don't feel any sharp points. File the corners down so that they are round. You can use some abrasive non-woven hand pads to make quick work of the edges.
Step 4: Making the Sides (part 3)
Use the box brake to bend the tabs 90 degrees. First, set the nose back from the joint about 0.032" (1/32") -- the thickness of the sheet metal. Next, bend each tab, making sure that the nose of the brake is right up against the bend line. It's best to use one corner of the brake, bend one tab, turn the piece, bend the next tab, and so on.
Step 5: Make a Body to Fit the Sides
Because we haven't done anything very precisely, we need to measure the width of the sides in order to make the rest of the box's body. Use calipers to measure first the width of the side. It will, of course, end up being somewhat greater than 3". Measure both of the side pieces across two tabs, and take the maximum. Let's call this measurement W.
About the best we can do is measure this to the nearest 1/32".
Do the same for the height of the side pieces, that is, across one tab. Let's call this measurement H, also to the nearest 1/32".
In the images, I have measured the width in two different locations, and the maximum is 3.141", which is nearest to 3 5/32", so this is what I'll use for W. The maximum measurement in the other direction is 3.073", or about 3 1/16", and so this is H for me.
Now we need to figure out the measurement of the body that fits around the sides. To do this, we need to take into account bend allowance. The diagram shows what happens when you bend a piece of sheet metal. The bend allowance is the size of that messy bit in the middle which you need to know.
The next diagram shows how a side would unfold, including its bend allowance. So what we need is a piece of metal that is 2 x H, plus W, plus 2 x bend allowance, whatever that is. There are calculators on the web, but just use 1/32" for now, which worked for me. If it works for you, great, if not, you can cut another sheet and try again with a different allowance.
So, use the shear to cut off another 4" length, and mark it as shown in the diagram. From one edge, mark off a line at H plus 1/32", then another line W" from that, and another line H plus 1/32" from that. Use the shear to cut at that third line.
Run a line down each of the long edges, 1/4" away from the edge.
Make a paper template with three lines, each 1" away from each other. Use the template to mark rivet holes in each section along the long lines, so that the middle mark on the template is at the middle of each section.
Dimple the rivet marks, and drill with a 3/32" bit.
Cut off the corners as before, and file the edges smooth.
Now use the box brake to bend at the lines into a U-shape.
The result should fit together as shown. If not, you may have to adjust the bend allowance if the sides aren't high enough, or W if the sides just don't fit.
Step 6: Match-drill the Holes
Next, we're going to match-drill the holes. This involves putting the box together, drilling one hole through both pieces, fixing the two pieces through the hole with a cleco fastener, drilling the next hole, and so on until the whole box is held together with cleco fasteners.
First, use the locking pliers to hold down one of the sides in place.
Then, using a #40 drill and holding a piece of wood on the inside, drill the middle hole. Put a cleco fastener through the hole to hold the pieces in place, and work your way outwards, drilling each hole and fastening with a cleco.
Do the same for the other side.
Now before you do anything else, mark the inside of the box so you know which side goes on which side! You can do this either with a marker, or you can make matching dimples.
Now remove all the clecos, and use the large drill bit to deburr each side of all of the holes by gently twirling it once or twice in each hole. It doesn't take much.
Now put it back together with the clecos.
Step 7: Rivet the Box
Now it's just a matter of replacing each cleco, one by one, with a rivet. Again, start from the middle and work your way out.
Step 8: Cut a Hinge and Attach It to the Box
Cut a length of hinge so that it will fit inside the box between the tabs of the two sides. You will probably want to use a vertical bandsaw for this.
Draw a line on the outside of the box, 1/4" from the top edge. This is the rivet line for the hinge. Punch a dimple in the middle, and then symmetrically near the ends of where the hinge will go, and drill with the 3/32" bit. Deburr.
Attach the hinge on the inside with locking pliers, making sure that the hinge is straight with respect to the edge! Match-drill with the #40 bit, cleco, take apart, deburr, cleco together again, and rivet.
Step 9: Make the Lid
Measure the dimensions of the opening box. The long side will likely be 4", since that's how wide the original sheet was. The short side will be somewhat more than the W measurement you made before.
Now cut a sheet that is 4 9/16" x (W + 9/32"). Draw lines on three sides (both short sides and one long side) 1/4" away from the edge. Note that we added 1/32" bend allowance wherever there is going to be a 1/4" tab, which is why one dimension is 4" + 2 x 1/4" + 2 x 1/32", and the other is W + 1/4" + 1/32".
As before, make dimples at the intersections, drill with a 1/8" bit, snip out the corners, file the edges, and bend the tabs.
Step 10: Attach the Lid to the Hinge
The lid should fit on the box nicely, so that if you open the lid, it will open all the way and not get stuck. You can try it now, before you rivet the lid to the hinge, to see if it will work. If not, you'll have to redo the measurements for the lid.
As with the procedure before, draw a line 1/4" from the edge of the lid, use the punch to make three dimples, drill with the 3/32" bit, attach the lid to the hinge with locking pliers, match drill with the #40 bit, cleco, take apart, deburr, cleco together again, and rivet.
In the image, I've actually waited to rivet the hinge to the box, and did all six rivets at once. Either way will work.
Step 11: Done!
Put something in the box, thus proving the essential boxness of what you've made!
Look at the box and think about how you would make the lid fit better. Maybe attach a handle to the lid. Spray paint it.