Building with MDF
MDF cores are not as strong as most lumber and plywood, but when joining together pieces of MDF, you can use just about any joint that you would use with plywood: butt joints with screws, biscuits, splines, fully rabbeted edges, and rabbeted tongues in dadoed grooves (see photos, right). You also can miter the edges if you want an invisible joint in a preveneered panel, but be sure to use plenty of glue on the mitered edges because they’re so porous.
You must drill properly sized pilot holes whenever you fasten a screw into an MDF edge; otherwise, it will split readily. For casework, I like to use a rabbeted tongue in a dadoed groove. This joint is not as important for the added glue surface and strength it may provide as it is for the assistance it renders when you’re assembling large cabinets. It makes the job a lot easier, especially when you’re working alone.
Deciding whether to use simple or complex joinery in cabinets is always a judgment call. Most casework is fairly simple, and it rarely has to be engineered to carry heavy loads, so butt joints with screws are sufficient. But when cabinets will be subjected to stress (a heavy television, a stone countertop) or abuse (young children who like to slam doors), don’t skimp on the glue and screws.
A Quick Tongue-And-Groove Joint on the Tablesaw
William Duckworth is a woodworker in Woodbury, Conn., and a former contributing editor to Fine Woodworking.