I first learned of this technique from another reader of this website. Don H. wrote to me & sent hand drawings about some of the techniques that he uses. (Don's instructions) I decided to give this a try & see how I like it. The answer is: I LIKE IT. I will probably Couch all my square cornered chairs from now on. It just gives the chair a more finished look.
Begin by whittling dowels down to about 3/8"-1/2" long & 1/4" diameter. Make these pointed so they will go into the hole & small enough that they will fit along with two ends of binder cane. The golf tee is presented to give you an idea of size. The smaller ones pictured were actually a little too small, the larger peg was perfect.
I started with the front rail of the chair & completed the binder as normal with the 7 step caning process. I cut the binder to fit from corner hole to corner hole & about 3/4" into each hole. I then cut to size the binders for the side rails, again about 3/4" extra for each hole. Insert the side rail binder into the front corner hole, along with a wood peg that has been dipped in glue. The wood peg should be sized to make a tight fit & use your thumb to press fully into the hole. A light tap with a rubber mallet can also drive the peg down.
Now bend the binder over the peg & form a neat 90degree fold. Work the binder up the sides as per normal 7 step process. Repeat on the other side rail.
Notice the neat corner that couching creates.
On the final (back) rail, leave a little extra binder cane on the end, perhaps an inch or 2. Couch the corner to begin the rail. As you work your way to the last corner, keep the binder ends in the last hole. When 2 or 3 holes from the last corner, create the final loops over the binder, but leave them loose to allow play in the binder. Insert a wooden peg under the last binder into the hole. Push down with your thumb, but it may also be necessary to pull the binder from underneath the rail, to tighten the last couch. Then finish up the loops. Tie off any remaining ends & snip off the excess binder cane under the rails.
This completes the nice 90 degree fold to give the corners a finished look, while also tightening & securing the binder cane.