The historical record is pretty clear. When it comes to chair joinery in vernacular furniture, most of the tenons and mortises are cylindrical. The most likely reason for this is you need only simple tools: a brace and bit to make the mortise, and a handplane to make the tenon. (You could also use a hollow auger, a lathe or several other methods to make the tenon. But using a plane is the simplest approach.)
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To make a tapered joint, you need a reamer to enlarge the mortise to the correct shape. The tenon can be made simply with a plane. (Or you can speed up the process with a specialty tenon cutter, a lathe or other gizmos.)
Reamers show up in the historical record as a shop-made tool or something manufactured by a blacksmith or other metalworker. But they aren’t terribly common.
When I first started making chairs about 2003, I didn’t own a reamer. So I made all my tenons cylindrical. It’s fast. And when done properly, the joint is strong.
Chris Williams and I have long debated the merits of tapered joints vs. cylindrical ones. In the end, the reason I used the tapered joint in “The Anarchist’s Design Book” (and teach the method) is because it is more forgiving.
When you bore a cylindrical mortise, there is no way to fix an error in your angle. You are stuck with the result, like it or not.
When you ream a mortise, you can adjust a mortise that’s even 10° off (I’ve done it). That is reason enough to ream for me. And the extra expense of the reamer is more than justified.
We could spill endless pixels comparing cylindrical or tapered joints, pros and cons, strengths and weaknesses. But in the end, I ream for forgiveness.
— Christopher Schwarz
Source: lostartpress.com