So, I am ok with establishing a good starting thickness. When I rough out a bow, I do just that. I make some sort of thicknessing device (could be calipers, could be vice grips, could be a board with a rectangular notch in it. I rough out to a consistent thickness for drying, say, 3/4" for most flatbows, mollies, and recurves, and 1.5x1.5 for an ELB or whatever. I touch it up when I start working the bow, and then I commit to a front profile and shape it to pretty close, except with wide tips. I have no luck at all marking a consistent thickness line and working down to it. We'll get back to that.
The trouble is, that everyone is right about the rest. From that point on, you just have to listen to the bow. BUT, I have to confess, I suck at floor tillering. I just can't see it, and I can't tell how hard I am pushing on it. Build yourself a tilering tree, or at least a cradle to hold the bow. Now, with a long string on, pull the string with the same force as the draw weight will be. Either use a spring scale and pulley, or hang a weight from the string with a hook.
If ABSOLUTELY NOTHING HAPPENS, you know the bow is too heavy. So remove wood evenly. You can either rasp the belly evenly to rough it up, then scrap[e it smooth, OR, if you are timid, color the whole thing with a dark crayon, and then scrape/rasp/spokeshave, it off. If the bow is way stiff, make 3-4 passes, and put it on the tree.
Now, for the faceted tillering thing. This is correct methid, but not exactly as you applied it. You DON'T do it all in one big step. Take your crayon, mark up the belly, and then get your rasp out. Use that faceted tillering technique to remove wood by removing your crayon marks. At a SLIGHT angle, rasp down one side of the belly, then the other side of the belly, then rasp down the high spot you left in the middle. This is MUCH easier and faster than trying to remove the wood all at once across a flat surface. Each time you do this you will remove 1/64"-1/100" or so, unless you are really horsing on the rasp.
Work this all the way to the fades, leaving them crowned or rounded in the middle, just a bit. At some point, the limbs will bend when you put the 50 lb weight on them (or pull), mostly close to the fades. The tips will move 2", or maybe 3". Are they even ? Does it bend the same? If not, do the limb that is bending less. Since the thickness is the same for the whole limb, the bend should concentrate near the handle. Once you have that even, just chase that bend from the middle out along the limbs, keeping it even.
Get out the crayon. Color the whole belly EXCEPT right near the fades. Mentally divide the limb into 4ths, say. Color the outer 3/4ths, and not the inner 1/4th. Then rasp and scrape that off. Then color the outer half, and rasp and scrape that, both limbs the same. Hang the bow on the tree and puill it with 50 lbs of force (or whatever) Does each limb bend the same amount? In the same places. Mark out any weak spots or hinges using the crayon on the BACK of the bow, and stay away from there for a pass or two. It will be bending a few inches now.
From here on, tree the bow, mark stiff spots with crayon, and then make the marks disappear. After a couple bows, you'll just stop using the marks because you'll get it visually, and can go right to the rasp.
Since I started doing this, the hardest part of the bow is roughing them out without gouging them, or heat treating without getting distracted and burning them.
