If you do any amount of repair work you will find that one of the most common repairs involves removing broken dowels. More properly removing a broken round tenon from a round mortise. You might think, that’s easy, just drill it out, the problem is it’s almost impossible to get the drill bit centered on the end of the broken dowel and if you drill off center you will damage the mortise. This is a simple method that is almost foolproof. This whole post may be to simple for some readers, but it may help some.
Here are the tools I use, a small saw, a bird cage awl [ a bird cage awl has a square profile at the tip, when rotated the square edges cut the wood fibers almost like a drill ], assorted drill bits and an incannel gouge [ an incannel gouge has the bevel on the inside of the gouge radius ].
This is, on the right, a broken tenon on a chair rung. On the left a mortise with a piece of a broken tenon glued in, the broken end has been trimmed flush with the small saw.
Here is the mortise alone. Trimming the ragged end off makes it easier to work on the repair. I have used the bird cage awl to start a hole in the approximate center of the piece of tenon. If the tenon had broken off below the surface of the mortise I would just use the awl to start the hole without trimming.
I next start to drill out the waste. I start with a small drill bit to establish a pilot hole for the rest of the bits to follow. In many cases there is a void in the bottom of the mortise and you can feel when the drill bit penetrates into the void, or you can watch for the bit to evacuate dried glue to keep from drilling to deep. You don’t want to drill through the piece.
Continue to drill with larger and larger bits until most of the waste is removed but you do not damage the mortise.
Pare away the final waste with an incannel gouge. At this point the waste will usually separate easily because the grain is running at 90 degrees to the mortise.
I show how I repair the tenons in this post.