Introduction: 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
Step 1: What You Need
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:
Ryoba Japanese saw
Bevel edge chisel (approximately 1/3 width of stock)
Step 2: Mortise Part 1
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
Step 3: Mortise Part 2
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
Step 4: Tenon Part 1
Knife in the shoulders and sides of the tenon, using the same dimensions as the mortise
Mark in the waste areas
Step 5: Tenon Part2
Saw the diagonals around the waste areas, to remove as much waste as possible
Chop and pare away the remaining waste material
Step 6: Test the Fit
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!
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