Juji Mechiire (a Japanese Splice Joint)

Here's how to prepare a juji mechiire (cross-shaped mortise and tenon splice)

Useful to extend upright posts, etc.

Videos in both English and German are available too

Although you can make this joint on round poles and non-square section posts, it's most simple to demonstrate with a square post. This should be squared all round with squared ends

The tools I'll use will be:

Steel ruler

Steel square

Marking knife

Pencil

Ryoba Japanese saw

Bevel edge chisel (approximately 1/3 width of stock)

Chisel hammer

The mortise depth is up to you. However, for this three inch post, I made the mortise an inch deep

Lightly knife the mortise shoulder around the stock

The mortise thickness should also be approximately one third the width of the stock, (but at least as wide as the chisel you'll use to make the mortise)

Mark the mortise position on two adjacent sides of the stock, and mark in the sides with a knife

Square the knife lines across the end of the stock, giving the cross shape

Clearly mark in the waste areas, to prevent mistakes

Saw the plumb cuts of the mortise, down to the shoulder lines

Now angle the saw and cut away as much waste as possible

Finish removing the waste material, by chopping and paring

Knife in the shoulders and sides of the tenon, using the same dimensions as the mortise

Mark in the waste areas

Saw the diagonals around the waste areas, to remove as much waste as possible

Chop and pare away the remaining waste material

To avoid splits on assembly, the parts should go together with nothing tighter than a sliding fit

Relieve any tightness with judicial paring of the joint surfaces, if necessary

If the two parts don't alight exactly, then plane them flush

That's all there is to it!

Thanks for reading my instructable.

Cheers,

Mitch