I have been building some shop cabinets using MDF. I am partial to drywall and deck screws, but I have noticed a tendency for the MDF to split apart even though I drill pilot holes for the threads and clearance for the screw body. What am I doing wrong? Any advice that you can give me to solve this problem will be greatly appreciated. – James Duermeier
Tim Inman: MDF is not very tough; stable, yes, but tough, no. Give your screw a meatier perimeter around the pilot hole, if it is splitting near the edge of the board. If the screw is “exploding” the MDF and swelling it as it goes into the hole, then your pilot hole isn’t large enough; use a bigger drill. Some drywall screws use a “double”-pitch (which is actually two unique threads wrapped around the screw shank) which makes them go in twice as fast – but with one-half the holding pressure. Others use a conventional single-pitch thread (one thread wrapped around the shank). See if you have both, and try them in a test. Does one type do better than the other? Sometimes the double twist pushes out less, so will hold better in MDF or strand board.
Chris Marshall: Along with Tim’s good suggestions, I would try to avoid getting to within a couple inches of the corner of MDF when driving screws into an edge. The material may still split some when the screw penetrates it, but the crack usually won’t migrate all the way to the corner. Tim refers to a double-pitch screw intended for melamine, particleboard and MDF: some manufacturers call this style Hi-Lo, and an image of it is shown here. When building with MDF, Ian Kirby actually won’t drive screws into the edge of MDF. He glues solid-wood corner blocks at these intersections and drives screws into wood instead. I’ve had mixed degrees of success when fastening MDF edges with screws. I tend to use glue and long brad nails rather than screws to help avoid these problems.