Through Mortise and Tenon

The through mortise and tenon has a parallel mortise that extends right through one member, and a tenon that extends at least the whole way through the mortise.
The two components are first prepared true and square.

A mortise chisel is selected with a width approximately one third the width of the connecting edge, and the pins of a mortise gauge set to this width too. The stock of the gauge is set to centre the pins within the width of the work.

The shoulders of the tenon are knifed around, using a try-square. The distance from the end being slightly longer than the final length, to allow for cleanup after the joint is made.

The length of the mortise is defined, by placing the components in the desired position and allowing for a shoulder at each end.

The sides of the mortise are marked with the gauge, working from the face side, between the two length marks.

The ends of the mortise are now knifed between the gauge lines.

The mortise is chopped a little inside the end lines, to preserve these lines intact until the last moment (chopping at the line to begin with will push the line away from the mortise due to the chisel's bevel).

Hold the chisel perpendicular to the work, so that the mortise does not end up angled.
After a light chop inside the line, the chisel is backed up a bit,

and another chop made, leaving the chisel in place.

Pushing the top of the chisel forward,

and then pulling it backwards,

levers out a chip.

Continue along the mortise, removing chips of a size that don't require a huge effort.
At all times, keep the sides of the chisel in line with the mortise, to produce clean sides and a consistent width.

For the last chop along the mortise, which is also held back from the end, reverse the chisel such that the bevel faces the other end.
Chop, but this time..

..remove the chisel, reverse it again, and replace it in the cut that it just made. You should find it automatically leans forwards, and can be pulled backwards to lever out the chip.

Continue to take passes along the mortise, until you reach the desired depth.

To finish off each mortise end, use a try-square to set the chisel at ninety degrees, with it's edge set in the knifed line, and chop down to depth.
Clean out all the waste, and scrape the base flat.

Pare from the waste into the knifed shoulder lines of the tenon, to create a knife wall guide for sawing against.

Use the mortise gauge to set in the tenon cheeks.

Saw the shoulders, using the knife wall to keep within the waste.

Make the cheek cuts by aligning the saw with the gauged lines on the end and one side first..

..and then following through to the other side.
Be careful to stay on the waste side of the lines.

Staying on the waste side allows for cleaning up the sawn surface, down to the knifed lines, with a wide chisel, router plane..

..shoulder plane, etc.

Use the finished mortise to align and mark the size of the tenon..

..and extend these marks to the length of the tenon.

Saw the tenon to size.
I make my tenons long, which allows me to cut a short section to size..

..dialing it in by test fitting..

..before sawing the section that will end up in the joint.

Once the tenon is fitted, and the glue cured..

..the majority of the excess length is sawn off..

..and then flushed with a plane.