Just to offer some other options: You can cut the rabbet using just your tablesaw using two cuts. With the plywood lying flat, cut the width of the rabbet. Then turn the plywood on edge and cut the depth. Use featherboards to hold everything snug so your fingers don't need to come anywhere near the blade.

A dado blade is the easiest option, followed by a rabbet bit for your router. The router will be easiest to control if it is mounted in a table. Again feather boards are called for however you choose to do it.

: I've decided to go for the ply strongback (for the ES); 16 feet is a *long*
: bit of 4x2 especially if I expect it to remain straightish for 6 months in
: a garage of fluctuatinng humidity.

: 1. I buy a full sheet of half inch thick plywood (8 feet by 4 feet)
: 2. I cut it on a sawbench into strips 8 feet long and either 2 or 4 inches
: wide.
: 3. Here's the problem: I need to cut 'corner off' along the long side of some
: of the strips. The pic below attempts to illustrate: +++++++++++++++++
: +
: ++++ P L Y W O O D : 0.5"
: ###+
: ###+++++++++++++++

: The bits marked # have to be removed. How? Is that what a router is for? Is a
: hand router good enough? etc etc.

: 4. Then I go on to glue it together into a v. long box; a sort of coffin for
: a boa constrictor.

: Regards,

: Francis.