This is how I get my groove on the belly of a Recurve
I put some masking tape on the belly and use some 120 grit sandpaper wrapped around a straight edge to cut the tape.
I use a 1/8" round rasp and a 5/32" chainsaw rasp
Just barely start a groove with the 1/8 and measure for center, I use the 3" line on the scale in the center of the groove and I can see it's off center a bit, I file again pushing to one side to get it centered.
I use the 5/32 just a little, not deep at all
I skip down a bit and do it again with the 1/8 and the 5/32
I connect the lines (still not to deep) and I have measured many times to make sure I going down the center.
The string groove is still to short to make it to the Y
I round over the tips <---> because they will be in the way when I bring my 2 string grooves together.
I put my string on there a mark with a pencil how far my grooves need to go. I needed a picture for that
I file with the 1/8 rasp, up the nock groove and round it over to the belly.
I also extend the belly groove to the Y
NOW I file all the groves deeper, I like mine down into the glass some, some people say not to do it but there are many 50/60 year old bows out there still working.