Stoping the groooove

Was reading yesterday Popular Woodworking's article on how to make a Kumiko lamp, and the guy says somewhere: "I know of no good way to cut these grooves by hand, or I would. Routers where made for this."

In my mind, I tried to imagine a japanese dude from the olden times with a router, plastic handles, and lots of noise, and decided that it has to be easy to make them by hand.

First, I tried the azebiki approach:

But I always have problems cutting beyond my line.  The other side was better:

The inside of the groove looks a bit messy though:

Then I remembered that the old man like to use a cutting gauge to define the lines, and then chisel away the rest:

4:50 is the mark you want to look closely at.

Then I had a second shot at it.

 The sides are way more defined than with the saw, and it's faster.  Another reason to not buy a router.