Dude, ADB did a post the other day called "tillering tree". Copy it and mount it on your wall. It is a very simple jig that you can build with a 4' 2x4, a few screws, and a little pulley. I got my pulley at a marine supply and it cost 30 bucks, no problem. Be sure to attach it strongly to a wall stud, because if you build bows you are going to be constantly exerting pressure on this jig.
Man i have made a fair few bows, always in the mirror. With the tiller tree you can exercise the bow (to its desired draw weight) very easily and safely and thoroughly: you need all these qualities in your tillering. If it is hard, you'll hate it. If it breaks and hits you in the head, you could lose an eye. And if you do not exercise the stave completely while it is becoming a bow, it could fail sometime later...which i think Mullet was just talking about with his yew.
I just made a tiller tree and in only a few days i see a huge difference.
Here's the process of using it and what you need.
a bathroom scale
a tiller stick (like the tree, marked with increments beginning at 12" and going through to 30") ... the tiller stick has a groove near the front to hold the string, and the bow is pressed downwards toward the face of the scale. I want a 40# bow. So i press it down til it reads 40#. If it says 12" on the tiller stick, then i know what to do on the tree.
a tiller tree (see adb's thread)...AFTER checking the weight and draw length on the stick and scale, move the bow to the tiller tree, centered upon it. Mine actually has a lip on it so the bow can't fall down ever. You hook the tiller tree hook onto the bowstring and pull the bow 30 to 50 times. Me, i don't watch much what it does...i let my eyes go out of focus, kind of, and see if anything jumps out at me...
After exercising the stave on the tree, i check it again on the scale. If it hasn't changed through exercising, then i go BACK to the tree with it and hook it at the proper draw length...in that case, 12". The i quickly use a tillering gizmo a la Eric Krewson (search it) to find the spots that need work. The gizmo marks them for you.
You then take the stave to the vise and remove the pencil marks left by the gizmo. Repeat this, and you will get a bow.
Breaking em sucks, i know. You just gotta pick up the next one.