A Woodworker’s Notebook
Jeff Gorman
Twin, Housed Mortise and Tenon Joints

A no-compromise joint for a fixed shelf that will help to tie together the sides of a bookcase or other carcase.

As well as restraining warping the housing covers the effects of long-term shrinkage in the thickness of the sides.

Twin tenons offer greater gluing area and when made as 'through' joints are, to some people, visually attractive. When wedged, the wedges can increase further the attraction.

Long-term shrinkage can cause the tenon ends very slightly to project. To allow for this shrinkage, leave a space between the floor of the housing and the shelf end.

The reach of most marking gauges is too short to enable you to follow the usual practice of working only from the face edge. Since you will have to gauge from each edge, you will need to ensure that the shelf is exactly the same width as the sides.

The care required to produce a good joint is suggested by the coding of the various dimensions.

If the wedges grip more tightly towards the outer face of the job, long-term shrinkage can cause the shoulders to open.

When driving in the wedges, take care to drive them at the same rate or you will find one sawcut irrevocably closed.

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