Start by making an exact width dado jig. Pretty simple to make if you look it up on YouTube.
Assuming you're using pre cut material, you'll line up 6 pieces. Find the center of the length. and then center a cross piece on that and mark the width. You'll use this marked piece to guide the dado jig to cut the center groove in all the rest of the pieces at one time. Clamp all six pieces together carefully and using an accurate square, align the jig 90 to the six pieces. Add a sacrifical piece to each side of the bundle to prevent chip out. Set the bit to cut to an appropriate dept, probably no more than 1/3rd the thickness of the work pieces.
Clamp everything up carefully while checking that everything is square and aligned. Clamp the jig in place and adjust it to exact width of the work pieces.
Make passes with a Mortising bit with a bearing.
Remove one piece from the pack which will become your vertical center piece. Position the remaining fice cross pieces on the center stick, moving them until you have the spacing you want. Mark their position, then set up the exact fit router jig (already pre-set for width. You will want to put in some mdf on each side of the center stick to present tearout, but also to add width to attach the jig. I would consider setting up an outrigger pair of sticks near the ends of the jig for added stabillity. Clamp down, rout the groove (2-3 passes) about 1/3rd the thickness of the piece.
I notice the 5 sticks stand proud a little bit, thus you won't cut to half the thickness.
Unclamp the jig, but not the workpiece, reposition to your marks, clamp, cut. and repeat for the remaining cross pieces.
If you've done this right, you will have a tight fitting, flat bottomed grove you can glue up, then use a decorative tie.
Another method using a pull saw, chisel and rabbit plane
Mark pretty much as discussed but also mark your desired depth as well. Being careful, use the pull saw across the workpiece and cut to just shy of the depth mark. I'd use an engineer's square to guide the saw. Cut carefully to the depth mark. Cut both edges of the groove (probably 10-12 pulls each cut), then make a number of cuts in between. Use a chisel to roughly clean out the cut, then a rabbit plane to flatten the bottom. I'd use a much wider piece of material to cut grooves, then rip the five cross pieces from that. The cross pieces only have one groove, the other, center piece has five grooves, but one is centered so you can cut it with the rest.
If this is being made of pine, I'd consider taking a good, 5 foot long 1x5.5, cutting it in half and gluing it into a panel wide enough to cut 6 pieces from. If you have the plane, a decent pull saw and sharp chisels, I'd probably just do it by hand. You'll also need a marking gauge to have a uniform depth mark. the pine will be easy to work with and you can generally find a decent 5 ft length of 3/4 pine.
You could also use a router plane to flatten the bottom, if you have one. It will give you greater accuracy on the depth of the groove.
OK, that's my take.
The more I do, the less I accomplish.
Last edited by DesertRatTom; 01-01-2017 at 01:25 AM.