Turn it on edge and hog it out with a dado stack on the table saw.

 

Do two saw kerf, whack the bulk of the waste in between with a chisel, pare to final depth.

Or use a plunge router to smooth the bottom to final depth. (the router on the edge, not on the face to avoid rounding in the corner)

 

Instead of cutting pieces away from the board. Glue the smaller sections to the edge of the boards spacing them where you want.
A small spacer block to keep the exactly the same.
Good Luck

 

I use a jig saw just outside of line, then clean to line with spindle sander, making sure the table is square to spindle .

 

I've used:

1. Shaper Origin
2. Milescraft circle cutting jig and palm router
3. Hole saw and hand saw
4. Chisel and mallet

EDIT Sorted by quality of results

 

Turn it on edge and hog it out with a dado stack on the table saw.

- bondogaposis

^Like this^
It also depends on: how long of pieces, how many pieces, how many cuts in each piece, what the size of the "U" is, it all goes into the decision making.

I have stacked 20 pieces together and used a straight edge and a router before. But like I say, it just depends.

 

Not sure how people are making round corners of the U with a dado stack.

 

Not sure how people are making round corners of the U with a dado stack.

- SMP

They're not. Us people, looked at his picture. What he is calling a "U" is actually a square cut out.

 

sigh

 

Not sure how people are making round corners of the U with a dado stack.

- SMP

They re not. Us people, looked at his picture. What he is calling a "U" is actually a square cut out.

- LeeRoyMan

Oh I thought his problem was that he wanted to turn his notches in the picture into U's. Oh then yeah, for notches a "good" dado stack.

 

The question has me confused. Is it a round U shape he is looking for or a square U (box) as pictured shape? Semantics can be so troublesome sometimes.

 

When I hear "U" I think opening for a router table fence, though not sure if OP meant Dado, Groove, or Notch

 

A lot of people have different terminology for things, but a picture is worth a 1000 words.
Since he posted a picture I'm 99.9% sure that's what he is after.

Then there is also this:
"1. Router - Kind of forces me to use a template, which is a pain to setup and of course leaves a tiny curve where the router can't get to the corners of the U."

But I could be wrong…
I guess we'll just have to wait for clarification. :>0

 

Well, I think you are correct LeeRoy. I must have missed that part where he mentioned the corner fillet as the particular issue he is having.

I guess in a strange sense, the fillets do make it a "U" and it's not that he wants help in creating a "U" but in notching a shape without the fillets.

 

Guess I learned how to write U's incorrectly all through school. I blame the p I_I blic school system