{"id":2634,"date":"2013-10-17T02:30:51","date_gmt":"2013-10-17T07:30:51","guid":{"rendered":"http:\/\/www.rpwoodwork.com\/blog\/?p=2634"},"modified":"2013-10-17T02:32:42","modified_gmt":"2013-10-17T07:32:42","slug":"thinking-about-the-mortise-and-tenon-joint","status":"publish","type":"post","link":"https:\/\/www.rpwoodwork.com\/blog\/2013\/10\/17\/thinking-about-the-mortise-and-tenon-joint\/","title":{"rendered":"Thinking about the mortise and tenon joint"},"content":{"rendered":"

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This will start a few posts here on sawing tenons by hand<\/strong>, but first let’s first ponder the mortise and tenon joint<\/strong> in general. A joint that has been used successfully for thousands of years certainly deserves some thought.<\/p>\n

What accounts for the joint’s legendary strength?<\/strong> Imagine trying to snap an “L”-shaped M&T construction. The mechanical lock<\/strong> of the tenon shoulders meeting the wood surface around the mouth of the mortise effectively transfers the imposed stress<\/strong> to the glued surfaces of the tenon cheeks against the mortise walls.<\/p>\n

The stress on the glued surfaces, in turn, is a shear stress<\/strong> – and we know how wonderfully glued wood surfaces resist shear stress. Voila: a strong joint!<\/p>\n

In fact, rarely will a reasonably made M&T joint itself fail. Rather, it is the wood around the joint<\/strong> that is more likely to give way.<\/p>\n

Looking at the mortise and tenon strength tests<\/strong> detailed in Fine Woodworking magazine issue#203 (February 2009)<\/a>, we can see that it is almost always the wood around the mortise<\/strong> that failed, even when the tenon itself was too weak to hold up. In the real world,<\/strong> I cannot recall seeing any decently made tenon break, but I have seen the wood around the mortise fail.<\/p>\n

I also observe that the only real danger to a tenon pulling out<\/strong> in a properly made joint is from the all-powerful forces of hygroscopic wood movement conflict.<\/strong> This may produce some gapping at the shoulder line, especially in injudiciously designed joints.<\/p>\n

In most woodworking instruction, much attention is paid to proportioning the thickness of the tenon<\/strong> with respect to the thickness of the rail. Recommendations are typically that the tenon should be 1\/3 – 1\/2 as thick as the rail itself.<\/p>\n

Yet, knowing from where the M&T derives its strength and how it is capable of failing, it behooves us to look at the proportions of the joint as a whole:<\/strong><\/em><\/p>\n