There are many ways to glue acrylic. This is the method I use when I want strong, clear seams.
Required: Weldon #4 or McBond acrylic solvent, and sewing pins.
The acrylic solvent creates the joint by dissolving a little bit of each piece, then evaporating out and letting the two pieces co-mingle, creating a strong bond. Contrary to popular belief, the joints are not stronger than the sheet. See
Here:
Weldon #4 is fine for small tanks and sumps, as well as skimmers and similar. If you are building a large tank, I would consider Weldon #40 though, it is 3.5 times stronger.
This method only works with the water thin solvents, like Weldon #4 or McBond.
The key to good clean joints, is a good edge. This can be made with a jointer, or with a router in a router table. If you cant beg/borrow these tools, you may want to consider using the gap filling Weldon #16 instead (Weaker joints than #4).
The following is the best method that I have determined- Modify as needed to fit the tools you have on hand.
Start by rough cutting the material on a table saw to 1/4" larger than needed. Make another pass though the table saw, taking off a little less than 1/8" on each side. This should leave nice edges on the piece, but it will be about 1/16 oversize.
Left side- Saw cut, right side- Jointed.
Using a jointer, or router and a fence, take off 1/32 on each side leaving a clean, smooth edge.
Lay out the bottom sheet, and brace the vertical sheet above it. Slide in a pin on each end of the sheet, and about every 6" in between. Most pins will be too tight/too loose at this point. Don't worry yet, just get them in place.
For each pin, slide in a wedge of wood under the bottom sheet, to lift it up until the pin is snug. Repeat for all the pins. Check them all again, pushing in each wedge a little until every pin feels the same, neither loose or pinched. Check one more time because if you missed one, that is where the bad joint will appear.
It should look like this:
(cont)