A fresh 10lb spool arrived at the end of last week, and I got started making good use of it.   I  wrap the spool in stretch wrap and pull the loose end from the center.   This keeps the spool from turning into a snarled mess, but does result in the cord getting wound-up as it's de-spooled.   It requires an extra step of unwinding after a length is cut.  After doing this numerous times for one backrest, I'm going switch to a lazy-susan approach and allow the coil to rotate as it's being de-spooled.  This should allow me to avoid the unwinding step.

There are a few ways to approach the weaving.   I'll be doing the wraps on one rail all the way across, jumping to the opposite rail, and doing both the rail wraps and the pairs of warp cords back to the starting rail.  Before starting, I marked the positions for the warp pairs on both rails.

Moving left to right, the near rail is wrapped, avoiding the areas that will later be filled by the warp cords.  I ran out of cord before even filling the rail - fortunately, doing this in segments is expected and knotted joins will be hidden since the backrest will be woven front and back.

At this point, I had completed the wrap on the one rail and am working back the other direction on the opposite rail, both wrapping the rail and adding the warp cord pairs.

The weaving slot is genius.  It provides an alternative path for the cord, allowing the front facing side of the rail to have normal rail wraps between warp cord pairs, but on the back there can be a wide swath of warp cords.   That wide band of cords gives knots someplace to hide when weaving the weft behind it.

The completed warp and wrapped rails.

Getting started on the weaving.    All of the free cord has to travel over and under all of the warp cords to weave a row, so to keep things manageable, this is done with segments of 80-90ft lengths of cord at a time.

Here, a new length of cord needed to be added.  You can see that there's an alternate weaving pattern on the wide band periodically.  This is needed because the 9 cords begin to bunch up.  To remedy that, the wide band is woven as if it were three bands of 3 for two rows, and then the normal pattern resumes.

It's easiest to form the knot on the outside to get it positioned just right, and then continue the weaving.

The knot hidden behind.

After a few evenings after work, I had one backrest complete.