I just made a hand-power one. .750" plywood base about 16" x 16", .& 250"
plywood screwed to it, shy ~2" on either side. A precision 1.25"x.75" strip
screwd along top @ far edge from legs, and a strip on the underside for
clamping to a bench vice. Then a 3x3 drill pattern through both plys for a
mitre strip of .750" x 1.000" x ~13" long, attached with a wing nut into
bolt held in grooves cut in bottom of .750" ply. A std. planer (whole
thing, not-attached, arm operated) rides flat on the .750" ply, up against
the .250" ply, on either side. The far edge strip is at 90 degrees, but
also micro-adjustable with a flat bottomed hole, and lat bottoming screw in
oversized C'Bored hole.
BTW, why is my No.4 Stanley plane flat (i.e right angled via. plane blade
plane) on one side, but not on the other!?