(I have updated my methods since I published this walkthrough. This approach risks getting dust in the box while it's being assembled and sanded. Updated method is here.)
Here's a mini-walkthrough on building one of the boxed images.
First off, decide on the dimensions of the base. In this case, I happened to have some pre-cut 7x9" cover glass, which was about the right proportions for the plate I wanted to box.
The actual dimensions of the box will be 1/2" smaller than that (1/4"+a tiny bit deep all around) to make the groove that will hold the glass and the back. So in this case my box' inner dimensions are 6-1/2"x8-1/2"
I cut the side pieces using a "mitre-izer sled" that I made from a few scraps of wood, glued together. I think you can figure out everything you need to know to make your own just from looking at this picture:
Make sure your saw-blade is true vertical or you're going to waste a bunch of wood. My mitre-izer has been constructed to fit 3/4" stock (to make it fit, just glue the pieces up with a piece of 3/4" stock in it that has a piece of gaffer's tape stuck to the side to make it a little bit thicker than the stock will normally be!) You see that stick coming out of the bottom of the mitre-izer? That fits into the mitre-slot on the top deck of the table-saw. Wax it well so it slides easily.
I used to use a wedge-block clamped into the mitre-izer to make the alignment perfect, but then I realized that eyeballing it really well is good enough. We're making a crafted wood box, not a space shuttle! Also, notice that my ruler runs backwards. You need to count the correct distance in inches.
Make a cut, flip the stock around, make another cut, etc. If you are a finicky woodworker you'll want the same side facing out, in which case you can chop the pieces to approximate length and put the mitres on them with your mitre-izer.
Check the alignment and length before you proceed:
Want to know what "woodworker hell" is? It's when you have the side of a frame cut 1/2" too short and you're in the middle of trying to glue the whole thing together. It's a wee bit too late to run to the saw and cut new side-pieces...
Next you're going to cut the grooves that the glass and back will ride in. Since the sides are 1/2" smaller, your groove should be a bit more than 1/4" deep on each side. The reason you need 'a bit more' is because unless you're using a dado saw blade that makes a flat cut, you'll have a slight ridge formed in the center of the cut-slot; that would interfere dramatically if you make things too tight for the glass to fit - glass doesn't squeeze really well. If you don't have a fancy gauge use a ruler.
I have standard dimensions I use - I like the bottom of the box to be about 1/4" up from the edge, and the glass to be 3/4" in from the top. So set your rip-guide to 3/4" and make a slice down the inner side of all your pieces. If you want to think about which edge will be the "top" and "bottom" of the sides, now is the time to spare thought for that.
Those are the grooves that the glass will fit into. Now's a good time to make sure your glass fits, by the way! If you have thick glass or a thin-kerf saw blade you may have problems. ("kerf" is the cutting thickness of a saw blade)
Now set your rip fence to where you want the bottom of the back to be. In my case that's about 1/4" up. I should mention, if you're not familiar with table-saws, that ripping slots like this is a great way to lose a thumb if you're not careful. Always use a pair of push-sticks for this kind of thing - I use one stick in my left hand (you can see it lower left in the photo above) to push the stock against the rip fence from the left and another in my right hand to push the stock forward into the blade.
The bottom slot is cut, but it's too thin to fit the 1/4" hardwood plywood I plan to use for the bottom of the box. Fortunately, there's an easy answer for that problem: creep the rip guide over a bit and make another cut. I usually just eyeball it and aim for 'a hair more' than 1/4" at the opposite side:
There's a special kind of saw blade called a 'dado' that can make wider cuts and is intended for doing this kind of thing. But to mount the dado, you have to unscrew the current blade and mess with the alignment and - meh - it takes seconds to do it this way instead of minutes to do it the other way. Here you can see the thin bit of wood left between the twin cuts for the back.
Just stick a sharp chisel into the crack (on the thicker side!) and twist and snap that thin piece right off at the base. You can see the piece on the right has already been cleaned out. This takes a couple seconds.
Now it's time to cut the back:
I have a piece of beech-faced plywood on the sled and have carefully measured it with a ruler. OK, actually, I just held the glass for the front up and eyeballed it, if you want to know the truth.
A sled like the one I am using above is a life-saver. Basically, it lets the entire piece slide along with the sled, so there's less chance the stock will shift or snag as it moves. The piece on the other side supports the cut-off part and makes it less likely to bind, fly off, and kill something on the other side of the room. This sled is a fancy one from Rockler that I inherited but you can make your own with a piece of plywood and a square, some glue and a couple of pieces of oak for the runners.
Mock-fit the whole thing together before you even go into the same room as your glue! Trust me - I don't know how many times I have tried to shave a bit off a glue-covered mitred corner, or cut a tiny edge off a piece of gluey glass...
This part was not immediately obvious to me, rocket scientist that I am, until I'd completed my first box: the inner face has to be sanded and finished before you assemble it, because it's really hard to finish and sand through that sheet of glass covering the front of the box!
In this case, I was finishing the maple with a wax and oil finish. Basically, what I do is give it a good wipedown with paste-wax and then let it dry, and hit it with a mixture of linseed oil and a hint of turpentine. When I was a kid I used to use wax mixed with gasoline but my parents talked me out of that.
Butcher's wax, by the way, is just beeswax dissolved in turpentine. I used to make vats of the stuff but now I am lazy and buy it in cans, premade. Why? Heating wax and gasoline is kind of like making your own rocket fuel. (Hint: use a hot-plate on "low" and a lot of patience) (hint 2: buy it canned)
Keep the finish clear of the mitred edges; you'll want the glue to be able to adhere. Use your waxy cloth to get all the dust out of the grooves if you can; you don't want the dust to re-appear inside your box once the glue is all set up.
Cut a piece of matboard to fit the inner dimension of the box. This is what you're going to mount your plate (and whatever else you use to make it!) on. The way I have come around to mounting my plates is by taking a leatherworkers' punch - the round kind that you hammer - and making holes at the corner, then lacing a ribbon or twine around the corners of the plate. I like the look.
Since I have a bevel-cutter for my mat-cutter, I actually bevel the edges of the matboard so that if there's any question whether it'll fit in the box, the beveled edges might go into the slot cut for the back. I've never had any problem, actually, but it gives my bevel-cutter something to do and makes it feel important.
Now, go clean the hell out of your cover glass, wrap it in paper, and have it ready. If you're the white cotton gloves kind of person, now's a good time to put your gloves on. I have learned the hard way that the best way to handle the cover glass is to unwrap it bit by bit as you bring each edge into play.
Here's the artwork as I've decided to mount it. Everything has little daubs of glue on the back to keep the strings from coming loose. I use a hypodermic with glue to put tiny drops inside/under the back of my little bow-knots. It occurred to me one day that if one of them came loose there'd be a glass plate whanging around inside a glass box and that seemed like a bad idea. So I have adopted a policy that everything is glued or wired or wrapped down tightly and permanently.
Sometimes I fantasize about just hot-gluing my plate to a block of wood so it floats off the back, but the idea of actually compromising the plate gives me the eebie-jeebies.
Consider how the sides of the artwork are going to work against the sides of the box. On this one I rather deliberately planned that they'll get rumpled against it. The folds in the paper, however, are all carefully glued into place. I wrapped the plate, then tore the paper open, then went along and tacked all the folds in place with my hypodermic 'o glue.
This is the box all laid up. I don't have pictures of that process because my hands were busy. First, I glued the matboard to the back, then took one edge of the frame and ran a thin bead of glue down the slit for the glass. This glue is to seal the glass so dust won't infiltrate around the edges. For this one, I used white PVA "woodworker's" glue. I ran a thin bead of expanding polyurethane foam glue (AKA: "gorilla glue") down the slot for the back and the mitred edges. I like the void-filling properties of the urethane glue but if you're not careful it'll swell out of the slots and into your artwork and ruin it. For the back-slots, be sparing. For the corners, be sparing at the inner edges near the artwork and less so at the outer edges. If you look in the "decoupage" section of your craft store they may sell these long-nosed glue applicator bottles made of polypropylene - those are perfect for applying glue in the slots; make sure it's something foaming urethane won't stick to.
I apply the glue in the slots and edges of one of the long sides, then insert the glass edge into its slot, and the back into its slot, and stand it edge-up on the table. Now, glue the slots in the short side pieces and assemble them onto the long-side piece you've already glued up. At this point you should be able to carefully rotate the box face up onto the table, holding the 3 sides together. Take a look at it; this is your last chance to slip a paper towel or a piece of rolled-up tape onto a chopstick and reach inside the box to fish out any dust, loose hair, or bugs that you got in there. A fingerprint on the inside of the glass, after this point, is permanent.
Glue and press the remaining side into position, and clamp the box together.
These clamps that I am using are a really clever rig whose design I stole from a buddy of mine. It's just polypropylene blocks cut with a scrollsaw, threaded rod, a bit of epoxy, and some knurled nuts. (I can't believe I finally got to use the words "knurled nuts" in a sentence!) I like this clamp a lot because you can put the corners in place, apply a bit of pressure, then squish everything carefully into alignment, and really tighten it down.
I let the box cure on its back because I theorize that any glue drippage is likely to go down. But, seriously, at this point there's no point in worrying. You either got it right or you didn't.
The next day, undo the clamps and - Tada!
Now we cut the corners for the splines:
Above, you see my "spline-o-matic" jig that I made. It's just 2 pieces of wood in a perfect 90-degree angle, slightly wider than my side-pieces, sandwiched between 2 pieces of plywood. The "slightly wider" is so that the box can drop between the plywood sides into the corner and rest there. As you can see, I took advantage of the plywood to write instructions to myself recording the "settings" for this spline-o-matic. The settings are the distance the rip-fence should be, and the height of the saw blade where it hits the corner of the box.
This should make more sense:
Here the box is in the spline-o-matic and the blade is at the right height and the rip fence is set. All I need to do is turn the saw on, and slide the jig forward to cut the corner of the box. If I were making another spline-o-matic I'd mount it on a piece of plywood with its own guide instead of the rip fence; that way I wouldn't get near the saw at all. As it is, I just hold the corner of the box near me and push gently then pull it back. Do all 4 corners then turn the box over and do the other 4.
Take your time figuring out the settings for your spline cutter. You do not want to cut up into the frame so deeply that you hit the glass where it's inset into the corner. When a table-saw tooth hits that glass sheet going 2,000rpm it'll make a hell of a mess. Not like I'd know. I'm just assuming, see?
A little foaming urethane glue to lubricate them, then press the splines in with the butt of a screwdriver. They should not be tight; they should be "just right" - especially if you're using wood that's contrasty - for example maple will expand and contract with moisture at a different rate from the rosewood splines you see above. Rather than figure it out, I just make sure it's not too tight. The foaming urethane fills gaps nicely anyway and is insanely strong.
Since the splines protrude past the edges you need to eyeball the edge-line to cut them off. I use the table-saw and my sled and am careful. Leave plenty of spline sticking out - it would really suck to hit the edge of the box with the table-saw blade and ruin it now.
This is my "paddy o'spline maker" - it's hard to cut a thin slice of anything on a big saw, so I made this sled with a right-angle stop (at the right/top edge) that will hold a thin cut-off piece. The block of ebony in the middle will get sliced to make a spline like the one at the mid/left of the photo. The angle piece at the bottom is used to hold the stock without having to get your fingers near the saw blade. I faced the angle piece with gaffer's tape because it helps keep it from slipping.
Now, here's a Big Secret - the right-angle stop is set back from the edge of the cut-zone to hold the spline that's about to be cut - how do we make it adjustable? Easy! See the built-up gaffer's tape on the face of the right-angle stop? Each strip of gaffer's tape thins the spline down by a, uh, gaffer's tape thickness.
The cross-hatched area means "DO NOT put your hand here" because the saw-blade comes through that area. I mean to spraypaint it red. Real soon. There is no such thing as a "minor table saw accident" and any time spent trying to think of how to make a jig that keeps your hands away from the blade is time very well spent.
Last step: sand the box
Because I like to live dangerously, I use my 'godzilla' belt sander to dress the edges of my boxes. It's fast. On the other hand, if the box slips out of your hand, your artwork is going to hit the wall of the shop going about 25mph. I wonder how an ambrotype handles rapid deceleration? So far, I haven't found out.
I have a pair of leather shop gloves that I took silicone caulk and put it all over the fingers and palms. For $10, a pair of 'sticky gloves' is really useful for sanding things you don't want to lose a grip on.
From here on, you can fine-sand it with an orbital sander and a less aggressive grit, then wipe it down with whatver you're using to finish it - and you're done.