Is there a list of tried-and-true doweling rules?

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Q:

Is there a list of tried-and-true doweling rules? I want to edge-join a pair of 34 ×7×48" ash boards for rocking horse rockers. How close to the ends can I place dowels, and how far apart can I space them?
—Charlie Stopcynski, Lawrenceville, Ga.

A:

We recommend making that first hole about 34 " from the end, as shown above, to avoid breaking out the end grain while muscling loose a dry-assembled joint in preparation for a glue-up.

For edge-gluing, the dowels align the pieces and keep their surfaces flush more than reinforce the joint. So space the dowel holes just close enough to correct any minor warping of the parts. For most edge joints, space the dowels roughly 10" apart, advises Jim Lindsay of O.M.S. Tool Co., maker of the Dowelmax doweling jig. Because you're cutting rockers from your glue-up, you'll also need to position the dowels away from your cutlines.

As for dowel diameters, use dowels half the thickness of the stock you're joining. For example, use 38 " dowels for 34 " stock, and 14 " dowels for 12 " stock. Drill each dowel hole 116 " longer than half the dowel's length —usually 112 " or 2" for precut dowels—to ensure a tight fit and allow space for trapped glue.