Read this from start to finish before you begin! Really! OK? OK!

First off, make sure that the pieces of acrylic you are using actually have square 90-degree corners. By following the order of assembly, as long as the corners of each of the pieces are a true 90 degrees, everything should line up pretty cleanly when you are done. There will be small errors that creep in, but these will mostly show up as the different panels turning out to be a different "height", and shouldn't affect the watertightness or usability of the unit. The one exception to this is that the partitions *have to match in length*. I'd had the shop where I bought the acrylic do the cuts for me ($1 per cut seemed cheap to save the cursing), but they didn't work to the most exacting dimensions, and I ended up having to sand everything to match.

To repeat: Make sure the partitions are identically matched and have true 90 degree corners!

For mine, I cleaned the partitions up by taping all three pieces into a sandwich, standing them up on edge, and sanding them with a stiff sanding block and coarser sandpaper until I was scuffing the edges of all 3 pieces uniformly. Remember to keep the sanding block perpendicular to the pieces as you do this, or you will sand in a bevel that will be annoying to deal with later. If you have a pad sander and a light enough touch with it to not worry about breaking the acrylic or sanding dips into the edges, by all means go for it. Either way, this will generate amazing amounts of acrylic dust, so be forewarned. Once the sandwich is nice and even and square-cornered all around, then go back and sand out the earlier sanding marks, this time using the 400 grit paper. You don't want to go any finer than 400 with the sanding on this, as I'm told it can cause cracking and crazing during glueup if the edges have a glossy finish. 400 makes a nice matte surface that should work fine. After cleaning up the partitions to match, clean up the cut edges of the pieces of 1/4" acrylic to have 90 degree corners, perpendicular edges, and a 400 grit surface too. The sides and ends can each be taped into sandwiches to make them match the way you did with the partitions to save time.

The next step is to groove the base and ends, so that the partitions will be easier to hold in place and glue up later. When you get to cutting each groove, you will want to cut the same groove on all 3 pieces before changing the adjustment to cut the next groove. If you make the mistake of cutting all 3 grooves in one piece, then cutting all 3 grooves in the next piece and so on, the chances of the grooves on all 3 pieces mating up perfectly once assembled are practically nil. Take the piece of 1/4" acrylic scrap, and make a couple test passes over the router table, adjusting the depth of cut until the bit is leaving a groove about 1/16-1/8" deep. I found that I could leave the protective paper on the acrylic and use the router at high speed and get away with it as long as I kept the plastic moving. No glazing of the bit, no melting of the plastic, and the paper kept the plastic from getting scratched by the table surface. Your mileage may vary. Once the depth of cut is adjusted, adjust the fence so that centerline of the cut will be about 1 2/3" from the edge of the piece. Once this is done, lock the settings in, and pass both of the end pieces down the table to make a longitudinal groove down the length of the piece, about 1/16-1/8" deep and set in about 1 2/3" from the edge. Then take the piece that is to be the bottom, and carefully but firmly place it down over the spinning bit such that the groove on this piece starts just a hair under 1/4" from the end, and pass it down, stopping just under 1/4" shy of breaking through the other end. (Note: If you accidentally just run it down and groove the whole length, it is recoverable, you'll simply have to glue up some holes at the end to make the unit watertight. If the finished slot isn't at least as long as the long side of one of your partitions, you won't be able to get it put together.). Once you've finished grooving both ends and the bottom as described, flip them around 180 degrees and repeat the process to end up now with 2 grooves, each set 1/4 of the way from the edge, running down the long dimension of each piece. Stop the router, pull out the scrap, and adjust the fence so that the last groove will be straight down the centerline of your workpieces. Cut the centerline groove from end to end on the two end pieces, and 1/4" shy of the ends of the bottom piece as you did before. Stop the router, take a break.

Check the fit of the partitions to the pieces you grooved in the last step. They should just barely fit into the stopped groove on the bottom piece, and should fit into the groove on the end pieces without a whole lot of play. Vacuum up all of the acrylic dust and shavings, peel the protective paper off of the acrylic, and wipe it all down with a slightly dampened chamois to get the last of the acrylic dust now when it is easier to reach than it will be after things are assembled.

Fill the solvent applicator about half full and make sure it is within reach, along with the masking tape, straightedge, and square before proceeding. Finding out you need something just out-of reach after you've started applying the glue is *no fun*. Take the partitions, stack them, make one last check to make sure they match perfectly, set them down in a stack, keeping track of the orientation. Tear off a half-dozen or more strips of masking tape about 8" long and hang them on the edge of the counter where they will be easy to reach when you need them. Place the base grooved-side up in front of you, then pick up one of the partitions, place it edgewise in the center groove of the base, and then use the masking tape to hold it perfectly perpendicular to the base, using the square to check for titlt one way or the other. I cheated in a sense, and taped the square to the base, then taped the partition to the other leg of the square. It worked, but I found out to my chagrin on the second attempt that the "rubber" leg of my square was susceptible to the adhesive/solvent, and had an interesting time trying to unglue my square from the thing. Once you have the partition squared up and taped up in the center groove, and placed within the groove such that you can later place the other two partition ends flush, then you can start the first glue-up. The "glue" you are using here should be amazingly thin and watery, like ether or alcohol, and works by dissolving a thin layer of each of the pieces, then evaporating, welding them together. Hold the applicator bottle upright, with the needle pointed away from your face, and squeeze gently to force a bit of the air out. Then turn the bottle over, the vaccuum should keep it from dripping as you bring the needletip to one end of the groove you are gluing. Slowly drag the needle along the groove, gently squeezing the bottle to allow the solvent to wick down the joint and through to the opposite side of the partition, dragging the needle slowly enough with enough flow that you don't get ahead of the line and leave bubbles which would cause leaks later. If the partition edge was straight, it should wick through surprisingly easily, painlessly, and bubble/gap-free. When you get to the end of the seam, relax your grip on the bottle as you pull it away to keep it from dripping on the piece. If it does drip a little, don't worry about it, it's simply cosmetic, but *don't* try to wipe the drip off, or you'll make things worse, just let it dry on its own. Also, once the solvent has been applied, *don't move the pieces*, or you may cause bubbles. This is why you so carefully checked the fit, placement, alignment before you started gluing.

After checking to make sure the partition is still stably taped upright, take a quick look at the seam. If there is a small bubble or gap, you can try adding a little more solvent to that spot now while things are wet and have a chance of it working. Then walk away and take a break. Not only will trying to go straight into the next glueup be hard to do without accidentally maladjusting this joint, but if you're at all like me, after gluing acrylic for the first time, it's time for a walk to let the head clear and nerves settle. Let it sit as-is for at *least* an hour so the joint truly sets up before proceeding to the next step.

Once the first joint is dry and stable, you can proceed to glue the next partition in. Take a look at the last glueup - if there are one or two tiny pinholes, wick a *small* amount of solvent in them to see if you get lucky. Then place the second partition in one of the two outer slots on the base, such that the orientation in coming off the stack matches up with the first piece (just in case one of the angles was a hair off). This time, in addition to being perpendicular to the base, you want to use the straightedge to make sure it is flush with the center partition. I simply placed the second partition such that it jutted out slightly, then held the straightedge perpendicular to the seam lien, and pressed gently to back it down until the straightedge met the edge of the center partition, making sure the two were flush. Tape the second partition in place as you did the center one before. If you've given the first glue-up several hours to dry, you may find you can tape the top edges of the two partitions to be just under 1 2/3" apart, parallel and flush. Wick the solvent in slowly and with patience. Again, you should be met with the pleasant sight of capillary action causing a fast wick, with no bubbles or gaps. Walk away again.

Third partition glueup is same as the second. Stressing again - make sure the ends of the 3 partitions are flush before the glueup! Two points make a line, two lines/edges make a plane, three edges can make a wobbly table, or, in this case, a leaky unit. Once you are conviced the three partition ends are flush, tape it up and glue as before. Now is also when you could try wicking a small amount of solvent into any pinholes in the last seam you did. After gluin this line, let everything dry overnight to make sure it is rigid and stable before moving on.

Once the bottom and partitions are thoroughly dry, we can glue on one of the ends. Start with the end of the assembly you were checking when you made sure the partitions were perfectly flush. Pick up one of the two end pieces, and try fitting it onto the end of the partitions. It should line up perfectly, with the edges flush with the base. If it doesn't turn it over and see which orientation is closest. Put a piece of masking tape on the ungroove side near the edge you decide is going to be "up", as a marker. Lay the end piece groove-side up in front of you on top of a few sheets of newspaper or a brown paper bag to raise it up off the counter a bit, with the "up" end farthest from the assembly. Then drizzle the acrylic solvent into each groove to fill the grooves without overflowing. Then tip the bottom and partitions into the end, so that the bottom of the endpiece butts up against the 1/4" of ungrooved end of the bottom piece, the partitions land in the grooves on the end piece, and the whole unit is standing on end. It may take a little fiddling with the partitions to get them to all rest in the grooves well. Rocking the edges in should help guide them while also minimizing the chanceof air getting trapped in the joints. Then hold onto the top of the end piece, and carefully rock the whole thing back to an upright position, keeping all the edges ans such together. Tape it up to keep the end piece itghtly butted againt the ends of the partitions, and the bottom edge of the end piece firm against the base piece. Wick solvent into the seam to attach the end piece to the bottom. If you can see any bubbles in any of these new seams, try dripping solvent down to them. If you aren't sure, go ahead and drizzle a few drops down each side of each of the new seams, as long as you don't go overboard or move the parts afterwards, it shouldn't do any harm. You want to end up with the end piece cleanly glued to the base w/o bubbles, and cleanly glued to the end of the partitions, again without bubbles. Ideally, this should also mean that all the edges and corners are 90 degrees, and that the end is perpendicular to the counter. If you grooved all 3 pieces of acrylic in the way described at the beginning, and kept track of which edge of the end was "up", the edges of the end piece and the bottom should be completely flush. Once everything looks right, leave it be for several hours or overnight to dry.

Time for the other end. Same as before, but first you should check to make sure that the entire length of the end edges of the partitions are straight and flush. If need be, touch up with a sanding block to make sure. After the glueup, let it dry 1-2 days to make sure the seams are rock-hard before the next step.

Place the asssembly on its side, and use the straightedge and sandpaper to make sure that all of the edges of the 1/4" acrylic are flush, smooth, free of nicks, chips, sanding scars, or stray weasels. Wipe up any acrylic dust or dirt you can see or find. It is about to get hard to reach. Place one of the sides over the asembly, make the edges line up, it should be pretty clean. make sure the bottom edge is flush, and that it overlaps the edges of the two end pieces well. If it doesn't match up quite right at the top, no worries - that's where we were letting the tolerances go, remember? Once you have it placed "just so", tape it down to keep it stable. Run around the edge with the solvent applicator, wicking it in along all 3 edges (side to end, side to other end, side to bottom), taking enough time. Now this may seem counterintuitive, but *don't* place weights on top of things, for the weight will make the side panel flex, pulling the edges up. If the fit-up was clean, it should dry-down nice and tight. Let it sit overnight.

Repeat for other side. Let it dry overnight.

Clean up any more acrylic dust you see, drizzle solvent into any pinholes left (if any). Once it is cured and clean, fill compartment 1 with water and let it sit for a few hours. If no sign of leakage, drain it, let it dry, then fill compartment 3 with water and wait. If still dry, then all the seams are likely to be plenty watertight and waterproof for use (The pedantic may notice that there is one untested seam this way, but it is clearly visible, and I make the assumption someone wouldn't try testing something that obviously leaks. If this seems unclear, let it dry, and fill compartment 4).

Congratulations! You now have a slot processor! To cut down on oxidation even further, consider rigging a sealing lid by cutting a rectangle out of a sheet of 3/4" closed-cell foam, similar to what is used for bleacher pads or swim toys, and use it to cover the slots between darkroom sessions.