Mortise & Tenon Joint Basics

Mortise & Tenon Dimensions:

  1. If your constructing your mortise with a chisel, then make mortise thickness 1/3 the thickness of the mortise board.
  2. If your constructing your mortise with power tools, then making mortise thickness up to 1/2 the thickness of the mortise board is acceptable.
  3. For tenon length, the rule of thumb is as follows:Tenon Length = 5 x Tenon Thickness
    Regarding the tenon length formula, this is a minimum value, longer is better (if feasible).
  4. For tenon width, the rule of thumb is as follows:
    Tenon Width = 1/2 x Tenon Board Width
  5. Tenon Length > Tenon Width, is desirable (However as a side note, biscuit joints do not comply with this requirement).

The Sketch below shows the tenon parts, regarding Length, Width, & Thickness.

Regarding the mortise & tenon joint, its best to construct the mortise first, and then cut (& trim as req’d, if need be) the tenon to match the mortise.

The Mortise & Tenon joint is used for the following:

  1. Panel & Frame construction (e.g. Cabinet Doors)
  2. Chairs
  3. Tables

Methods of making Mortise & Tenon joints:

  1. Mortise by chisel & Tenon by handsaw.
  2. Mortise by powered hand drill (square up corners with a chisel) & Tenon by Table Saw.
  3. Mortise using a dedicated powered mortiser & Tenon by Table Saw (or Tenon jig used in conjunction with your Table Saw).

To get Mortise centered exactly when using a Dedicated Power Mortiser, after drilling mortise, rotate wood to put opposite face of wood against fence of dedicated power mortiser, and drill again. The mortise should now be perfectly centered.

The two Sketches below show two frame boards for a frame & panel setup. The two frame boards are grooved as shown to accept a panel that would be inserted into the groove on the frame boards. The notched tenon closes the groove in the framing boards as shown. The longer portion of the tenon shown fits inside a mortise in the adjacent framing board.

The first Sketch below shows how the notch (shown enclosed by a circle & pointed to by “A”) closes the groove in the vertical frame board (the location circled & pointed to by “B”).

The next Sketch shown below, shows the tenon (circled & pointed to by “A”). The vertical framing board shows the location of the mortise (circled & pointed to by “B”).

If you have not used the mortise & tenon joint, try it out. You’ll find it to be a surprisingly strong joint.

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Until Next Time, Take Care


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