Flush trim router bit allows you to duplicate a master pattern or template. You can use it to create exactly the same shape multiple times over with similar pieces of timber.
How does it work?
First, take the template piece. Draw traces on your second piece of timber. Make a rough cut to this outline, making sure to cut outside the trace line, so it's slightly larger than your template.
Put the template underneath first, then clamp the larger roughly cut section on top. Clamp these parts to the workbench.
The bearing in the flush trim level is in contact with the reference piece throughout the process. The blade makes contact with your rough cut, giving you a perfect copy.
The result is smoother than what you get with a bandsaw and so simple to do, especially if you need to make a lot of pieces the same.