Because biscuit joints are easy to mark out and quick to cut, using one almost seems like cheating. The safest way to cut biscuit slots is with a biscuit joiner. The oversized slot lets the biscuit move slightly, enabling you to tweak parts into perfect alignment.
Properly-cut biscuit joints are strong and accurate, particularly when cutting slots with a woodworking tool called a biscuit joiner. When glued into slots precisely cut by the biscuit cutter, and the moisture from the glue causes the biscuit to swell and tighten the joint. As a general rule, try to use the largest size biscuit possible, as this will provide the greatest amount of strength to the joint.
“The slot for a #0 biscuit measures about 21⁄8” wide, so you can’t hide a biscuit joint in stock narrower than this. Even a well-tuned biscuit joiner can sometimes cut slots that result in a non-flush-fitting joint. Cutting the spline slots on your tablesaw requires a tall jig, but you can cut them easily and quickly with your biscuit joiner and the attached fence jig, see drawing below.
how to join boards with a biscuit joiner Related Question:
How many biscuits should I use to join wood?
Two biscuits per foot is a great rule of thumb, but the goal is just to make the alignment task easier. So, if you have a couple of edges that are 24″ in length and are dead straight & perhaps you would only need two biscuits to do the job.
Are biscuit joiners worth it?
Biscuits joints serve best as a quick and easy way to keep glue-up parts in alignment, and that they add appreciable pull-apart to strength joints that would be otherwise too weak to stand on their own – like butt joints and miter joints.