Bill,
I have been doing a lot of work with this stuff lately (combo refugium/protein skimmer, some cuvets for the lab, and currently a light fixture for some 55watt cp flourescents) and I will share what little I know. Lexan, Lucite, Crystallite, Plexi,... Its all pretty much the same stuff. What you want to build your tank with will be called die cast acrylic (under any of the fore metioned brand names), as the dye cast has the greatest machineablity (I think all the thicker sheet stuff is dye cast anyway). I would go at least 1/4 inch, 3/8 will show much less warpping on large load bearing areas (like the bottom of the tank). The stuff is expensive- localy 1/4 runs about 4.00$ a square foot and almost 10.00$ a square foot for 3/8.
The glues are made by Weld On. There are two types commonly used and you will want both on hand. Weld On #16 is a thickend cement and it works well at filling any small gaps or sealling any mistakes (but it doesn't come out supper pretty). Weld On #4 (I belive thats the one) is a water thin cappilary glue that forms amazingly strong joints, but it requires very precise fits between pecies. However, when done right the piece appears seamless.
I found a table saw blade designed for finsh cuts on thin plywood to be perfect for cutting the stuff (I belive the one I used was made by Skill and cost about 12.00 at HD). Most router bits work well too. And a Dremel with a carbide cutter will be very helpful. If using a jig saw, go slow with the blade moving at about half speed. Otherwise, after finishing the cut you will find the two pecies fused back together.
Wait 24 hours after a glue up before polishing (this is the fun part). To polish it, sand the edges smooth and take a blow torch to it. I found that 1/4 inch was by far the easyist to polish. 3/8 cuaght fie much to easy for my taste. Anyway, play around on some scrap first to get the hang of flame polishing.
One other thing, if you use clamps to hold joints together when glueing with the cappilary glue don't clamp it very tight. If you do the glue want move into the joint at the clamp and you will get an un-fused area.
I hope this helps.
