This excellent and thorough article from 1980 was linked in a recent FWW post: https://www.finewoodworking.com/1980/04/01/the-dowel-joint
Well worth a read as I have no doubt that the principles have not changed in that time.
In summary it points out that dowel joints fail all the time due to moisture related changes in the wood. Expansion and contraction loosens the joints, with severe 6% to 24% to 6% cycling causing failure in just one cycle!
It would be interesting to see if this also happens with tenons. Has anyone done similar work on the best way to create a lasting tenon?
Does anyone know if there is a follow-up article to this one? Certainly there have been developments in adhesive technology in the last 40 years.
@Mike Pekovitch has more than once stated that chairs are items with a limited life. Perhaps this is due to a degree to the tenon structure and the way they are constructed.
ALSO the article suggests that a dowel joint should be about 1.5 times as deep as it is wide, but once it gets to 2 times as deep as it is wide, you get other problems, which are darkly hinted at, but not further explained. I can see there being little benefit in the deeper hole, but wonder if anyone knows what the problems are?
Perhaps FWW might consider a well-researched series of articles on why joints fail and how to prevent it…
Replies
Mike Pekovich recently did a video on the draw-bored mortise and tenon, and there are numerous FWW articles. IMO that is the best way to use a dowel. Two other ways are decorative purposes or to help align pieces being glued together. I don't believe they are strong enough to reinforce a butt joint, even though much furniture is factory mass produced that way.
There is a large camp of folks who use dowels and believe them to be a reliable long term joint. Those of use that have repaired about a zillion failed dowel joints have empirical data to the contrary. I use dowels, just not at stress joints.
Like biscuits, floating tenons, dominoes, etc., we choose our joinery methods for the purpose at hand. Choosing the same method for every purpose is where things start to break down. To each their own.
I rarely used dowel joints in my furniture building days, but when I did, I used dowels that had been kiln-dried, then machined slightly oversized, then had spiral grooves pressed, not cut, along their full length. I always used water-based glue to re-expand the dowels. Cutting across trial joints once they had cured showed that the contact between dowel and workpiece was perfect. I have never had a problem (or a callback) with such a joint.
-- Mac
When glueing edge to edge or edge to face dowels work fine, not my preferred method but it works. Once you drill a hole perpendicular to the grain, that portion of the joint is 50% or more end grain and with time it will fail. If you’ve ever seen a chair that fell apart the dowels are usually still sound in the apron and have pulled loose from the leg. ( in my humble opinion) hope this helps
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