Q: I recently had to repair an exterior wood storm door and thought it was a perfect excuse to try a biscuit joiner. I disassembled the door and found that it was held together with hardwood dowels. After replacing the dowels, I was wondering if there is any rule of thumb as to when to use dowels or biscuits.
A: I’d look at a couple of things. Are you trying to reinforce the joint or simply align the parts? Because of the deep penetration you can get by inserting long dowels, they’ll provide more joint shear strength than biscuits. My primary application for biscuits is as alignment aids. However, dowels can be much fussier to work with. You can’t beat the side-to-side adjustability and ease of installation with biscuits.
A second consideration is the size of the parts you’re assembling. Even the #0 biscuit — the smallest conventional size — needs a slot about 2" long. This won’t work on a face frame with 1-1⁄2"-wide rails. The more recent face frame biscuits, and other specialty sizes, can help solve this problem, provided you’ve got a machine that can cut the smaller slots they require.