I am thinking of building some MDF build-in bookcases, dado joints are clearly stronger but creates lots of mess from a router and takes more time.
As the book case will be painted, I can hide any screw heads, so that is not an issue.
I see 4 options:
- Just screw and glue the shelves to both the sides and back.
- Dado, screw and glue the shelves to both the sides and back.
- Dado to side, screw to back.
- I could also make “cheat” Dados by gluing 6mm MDF onto 15mm MDF on make the sides
Dado at the back means I need a thicker back that will make then harder to build due to the mass. However I don’t know if screw joints into the end grain of MDF are strong enough, I am thinking of using 18mm MDF for the sites and 30mm MDF for the shelfs.
I am thinking of using spax MDF screws as they don't need predrilling etc.
(I am not asking this on a woodworking site as I do not have great woodworking stills and care more about the result then the process.)
Best Answer
I built a bookcase from 3/4" (19 mm) MDF back in 1985 to hold heavy, oversize college textbooks. It's three feet wide with two twelve inch deep, fourteen inch tall shelves. It has not bowed under the weight in 27 years. The shelves are are attached to the side uprights with four screws on each end. The back is 1/8" masonite, well secured with screws. 1.5 inch rails attach the end boards at the bottom also at the back of the top.
Judging from the stability of the bookcase under heavy load for a quarter century, I'd say that dados are not necessary.