I have ordered flush wood vents with a frame dimension of 13" X 6 3/4". I set up my router table with a 1/4" carbide end cutter to cut the grooves in the planks for splines. But I am not sure of the best way to cut the 3/4 X 3 1/4 planks that join the vent. The vent supplier suggested to cut each plank so that it ends in the middle of the long side of the vent and then make a L shaped cut in each plank with a Scroll Saw. This way doesn't seem very precise and I think it would look neater without a seam at each vent. How do you experts install these vents?
All help and suggestions are greatly appreciated.
Thanks,
Luther

I try to have one long side tie neatly to the edge of a floor board without cutting, then just cut the next course around the register. I'll use a table saw for ripping boards length wise and a powered miter saw to make cross cuts. Very neat that way with no chipping of the wood. You can spline into the wood register but it isn't mandatory. Another option is to cut down the width of your register by 1/8" on each side to make it 6.5" instead of 6.75". That way, two courses of your 3.25" flooring will fit neatly to the ends of the register and you won't need to make any rips. Keep in mind you can off set the wood register by a 1/2" or so over the opening to allow it to fit the flooring better if needed.

since you have that router handy you could make a plywood template and just route them out as well. I would make up a dummy to test on the first time if your not comfortable, you will have to make three or four passes to cut through 3/4 flooring. try not to nail in the path of the cutter head nails will ruin your bit in a hurry. Good luck..

Thanks for your input guys.
I need to give you some additional information. My starting wall has two floor vents 2 1/2" form the wall. So if I subtract the 3/4" expansion gap and 1 1/8" for the vent frame that leaves only 5/8". In addition, I will eventually come to three more vents. Two of them will be 2 1/2" from the wall and the third will be 4" from the wall. There two ajoining rooms and the total width of the flooring will be 37', so I don't want to reduce the 3/4" expansion gap. In fact, should I allow a slight gap in the planks every 3' or 4' since the total span in so large?
My Router needs 2 3/4" from the edge of the base plate. Should I cut the first plank before nailing it down and then route the remaing planks in place to fit the vent frame?

Luther

Honestly if this is an unfinished floor then I would just use the miter saw for the parallel cuts and rip the long side on the table saw, if you dont feel comfortable with that a jig saw and a steady hand will do just fine as well. On the expansion, 3/4 expansion in my humble opinion is overkill, a floor that is subject to that much movement would have to be flooded, and the expansion would be the least of your worries. imo 1/2" from the sheetrock is adequate for most floors.

I only use my router to cut register openings when doing a retrofit of flush mount registers in existing floors. Routers are great but they are slow and make a mess. And the bits are expensive. Kev's right about the expansion space and I've said the same thing myself before. The table saw and powered miter saw work much better than a jig saw for making straight, even cuts. Take it from someone who tried both ways. Just cut the flooring around your register. What choice do you have unless you want to relocate the HVAC openings?

The flooring is Bruce prefinished. thats why I am concerned about what I use to make the cuts. I have a powered Miter Saw and a radial Arm Saw.
Do you tape before cutting to reduce the possibility splintering the finished surface?
Thanks,
Luther

Only when using my circular saw, which cuts up into the work piece. I do not like using a radial arm saw for ripping. It can be done but I think it's not that safe or accurite. By using fine tooth saw blades and going slow, you minimize the possibility of splintering the cut. A table saw and miter saw are still you best bet, IMO.

Thanks to everyone for your valuable help. You got me going in the right direction and now I am going to get busy laying floor planks.

Best regards,
Luther