Tenon Fabrication

What is a tenon as it applies to timber framing? By definition, a tenon is a projection on the end of a timber used for joining multiple members together.  Timber frames receive a multitude of handcrafted tenons and each tenon is created with great care and will end up joined inside a mortise.  A tenon starts life as a set of lines on the side of a timber post, beam, or knee brace.  Each line is drafted using the timber frame shop documents as a guide for length, width, and placement.  This is referred to as ‘laying out’.  Every member of a timber frame is laid out and checked before it is fabricated. 

Once the tenon is laid out it is time to double-check the work, grab a saw, and start cutting.  Our crew uses different sizes of circular saws to make the various cuts required in fabrication.  Once the saw is set to the correct depth the cutting can begin.  Depending on the tenon length this is usually a series of four cuts.  One cut on each side defining the position of the tenon and two additional cuts to remove the waste material.  At this point, we have the basic shape of a tenon.

The tenon is then evaluated for consistency and accuracy.  Any imperfections are worked away with a chisel.  Using a mallet and chisel, the joiner takes care to skim off waste material and leave behind a work of art that is ultimately hidden within its respective mortise.  Although never seen again, accurate tenon fabrication is crucial for a tight-fitting timber frame.  The more accurately the tenon is cut is directly related to how well the members of the frame fit together.  Too short and you end up with a sloppy joint, too long and the tenon sticks out of the mortise.  Our shop crew creates tenons so accurately that they receive a bevel at the end for easier fitment. 

Once a series of mortises and tenons are cut, it is on to pre-fitting the frame in sections.  During the pre-fit of the timber frame, the peg holes are drilled through the assembled mortise and tenon joints so that once raised, this geometry translates to the assembled frame and is truly a hidden work of art.  The frame seemingly squeezes itself together along with the raising crew to perfect fitment but in reality, it is the skill of the joiner that creates this illusion.