Dado Versus Dowel Joinery in Furniture
From contributor J:
I use biscuits for my casework, but I think the dado method would be stronger at supporting heavy loads. The dowels will work fine also, it just depends on the piece itself.
If you need more evidence, then build two identical units, one with dadoes and the other with dowels. Now try to make them fail by placing heavier than normal loads and racking them. That's how you will know for sure.
I think contributor T is thinking about actual furniture, not the stuff you find in dorms.
From contributor W:
If you can take the time, I would use shelves with two 2" wide tenons on each end put into corresponding mortises in the sides. A 3/8" deep dado would help also. I am assuming using 3/4" stock (birch ply or solid).
From contributor B:
Mortise and tenon construction provides a large long grain to long grain glue joint. The grain is going in opposite directions, but it is still a large glue face. This makes for a strong glue.
Dowell construction gives very little long grain to long grain mating in the joint. Just look down a cross-grain drilled hole and you'll see there is only long grain on two opposite sides. Since there is little or no strength in butt joint gluing, you end up with a weak glue joint.
That doesn't necessarily mean that dowels make weak joints, though. Whereas you may have a weak glue surface, you still have a joint with a lot of rigidity and shear strength. Plus, you can add as many dowels as wood size reasonably allows.
Bottom line is that your choice will depend upon the end value of your product. A mass produced inexpensive item easily justifies doweled construction. On the other end of the scale, a museum quality piece deserves the extra time and attention required to produce mortise and tenon joints.
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