TILLERING YOUR BOW
Now that your bow is completely shaped and able to be strung, the next step (after you've shot it a time or two of course) is tillering the limbs. First lets take a look at the definitions of tiller and tillering.
Tiller is the difference between the upper limb and lower limbs measurements from the bowstring to the belly at the fadeouts. Bows are traditionally tillered to produce a stiffer lower limb; ie, the bowstring to belly measurement on the lower limb is less than the same measurement on the upper limb.
Tillering is the adjustment of tiller by removing material from a bow limb or limbs. Most bows are tillered to approximately 1/8" - 1/4" positive measurement on the upper limb, when the bow is to be shot split fingered. I tiller my bows even for a 3-under shooter. The following picture shows two methods of measuring, one using a bow square and the other a clear plastic ruler. Make sure that you always measure perpendicular to the string for the greatest accuracy.
The methods used to tiller a bow are quite simple. One method to use is to slightly narrow the strong limb. Another method is rounding the edges of the limb and the 3rd method used is to flat sand the fiberglass, thereby reducing the thickness of the limbs. Remember to go slow here, since removing material is easy but putting it back is impossible.
Once I get a bow to where I think it is close, I will then string it, put a nockset on and go outside with nockset pliers in my back pocket, and fling some arrows. I then tune the bow by adjusting the nocksets location until I don't see any porpoising of the arrow. If the nock set is unusually high I then take the bow back in and readjust the tiller.
Bows will vary on the amount of necessary tiller depending on design