Steve Stevens

The body mortise is begun by making the two angled side cuts.

Here a Japanese pull saw is being used.  Any fine toothed saw will work.  Since the grain on the neck block runs in the same direction as the grain on the sides, a saw with cross cut teeth is the saw of choice.   Hold the saw cut inside the layout lines to be safe.

I like to stop the mortise about 1/2" to 5/8" from the back.   Every guitar will be a little different, so make the mortise fit the guitar you are working on.

Once the saw cuts have established the edges of the mortise, the remaining wood is removed with chisels and knives.  The neck block on this guitar is 1 1/2" thick.   That means the 3/4" deep mortise in the body will only be cut half way through the block, leaving a good safety margin.  The cut across the spruce has been made taking several shallow cuts and the mahogany neck block wood has been chipped away.

As the cut continues, the side angle of the mortise is maintained by shallow tapping cuts along the sides.  Easy does it.  Use many cuts with a sharp 3/8" to 1/2" chisel.

Resist the urge to use a wider tool as the wider the cutting edge is the greater the force needed to complete the many cuts needed.  Keep the mallet blows light to avoid splitting the neck block.

After the mortise is completed, use a very sharp 1/2" to 3/4" chisel to shave the walls and bottom of the mortise into nice continuous clean lines.