Using a biscuit joiner and biscuits is a great way to join multiple pieces of lumber so the boards are aligned during glue up…this is a big time saver. One issue that can arise if a biscuit isn’t placed properly is called “telegraphing”, which means that a biscuit can contract over time and pull the surface wood down with it creating a slight depression, or indent in the surface. Here are some simple tips on using a biscuit joiner and how to prevent telegraphing.
WRONG: In this example, the biscuit is placed too shallow in the board, which will promote telegraphing over time.
CORRECT: Set your biscuit joiner deeper to about 3/8″ from the top of the biscuit to the top of the board to prevent telegraphing. If telegraphing does happen, it will be on the underside or the surface and will not be visible. Another way to prevent telegraphing, especially when joining thinner boards is to NOT add any glue to the biscuit slot.
These clamps from Rockler come in really handy when joining the boards with biscuits after glue up.
I like to use a little sawdust and a wet rag to clean up the glue squeeze out. Cleaning both the top side and underside of the joined boards while the glue is still wet prevents a lot of extra sanding before finishing.