There are a few ways to accomplish the top flange (the rim or one-piece euro-brace) of a sump. Originally, I would build the sump, squeeze in pieces of wood inside the upper edge of the sump, and use a router with a ball bearing guide to trace the lumber. This was tedious, and cutting wood for each sump would end up costing too much.
How would you like to route some teeth for a baffle of your sump? Here is one of the methods I've used.
You could create a "jig" that is re-useable, such as the thumbnail to the right. It provides me with a series of grooves for the router bit's shaft to trace, but over time it melts the material of the jig and has to be replaced. This is a good choice for a few uses, at most.
Due to the abundance of emails, it was time to put some pictures on the site. Here are a number of items I use to build the sumps and other acrylic wares I fabricate. While not everything is absolutely necessary, I find that if you have the right tools on hand, your end result will be better. Keeping track of all these items can be a task, since they scatter during the construction phase...