Loose Tenons
I have long been of the opinion that flat tenons are stronger than dowels, but I have forgotten why. I assume that the answer lies in the amount of long grain to long grain that each allows. Anyone care to discuss?
Thanks,  Curt
"Life can only be understood backwards; but it must be lived forwards."
      -- Soren Kierkegaard
  Re: Loose Tenons by cputnam (I have long been of ...)
I don't think there is much to discuss.  As you pointed out,  dowels have very little long grain to long grain.  They can also swell and shrink differentially.  The main advantage is that it is much easier and cheaper to drill a hole than to chop a square mortise
  Re: Loose Tenons by cputnam (I have long been of ...)
I recently  had an interesting experience with doweled joints. About 40 years ago, I started a project using dowels instead of tenons and mortises (not sure why). We sold the house and moved across country to CA, than, eventually to Canada. The project (along with my woodworking tools) were packed away. Recently, we cleaned out the storage area and I found these oak pieces. Many had mold on them, so I decided to turn them into firewood. I had to hammer those dowel joints apart!  Never thought dowel joints could be so strong!

Demonstrating every day that enthusiasm cannot overcome a lack of talent!
  Re: Loose Tenons by cputnam (I have long been of ...)
R. Bruce Hoadley (RIP) wrote an article in FWW years ago about weaknesses in dowel joints.   As said above, minimal long grain to long grain surface and differential seasonal expansion were the main reasons, IIRC.    https://www.finewoodworking.com/1980/04/...owel-joint
  Re: Loose Tenons by cputnam (I have long been of ...)
Less surface area for glue contact as well. Let's say you're making a door frame, and the stock is 3/4" x 2" wide. A typical mortise and tenon would be 1/4" x 1" w x 1" d. So, total glue area would be 1/4 + 1/4 + 1 + 1 = 2.5 sq in for a classical integral tenon, or 5.0 sq in for a loose tenon. If you used two 1/4" dowels and put them in 1" deep, you'd have 1.67 sq in of area per dowel, or 3-1/3 sq in for two dowels. So, a loose tenon gives you 50% more glue area compared to dowels.
Still Learning,

Allan Hill
  Re: Loose Tenons by cputnam (I have long been of ...)
Curt, I think it’s not so much the surface area but the section. Mortise and tenon joinery is well suited to in-plane loads seeking to alter the angle of the joint (moment). Engineers might call the reaction, heel-toe or maybe socket action. If you made mini tenons, they would be just as crappy as dowels. It’s the distance over which the moment is reacted.

I think one advantage dowels offer is that, if you have the right drill bits and dowels, you can get a tight fit, which helps.

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