This is a GREAT video series. This is the one on tillering. It really helped me as a beginner to get whole picture.
https://www.youtube.com/watch?v=UXrcV4iVq74My take and I am a newbie. Sometimes I think the masters just don't explain the obvious to them things. Masters, PLEASE correct me, if I am wrong!
You have a stick.
You shape the stick to your bow type that you have chosen but it is too thick to bend.
You thin it to the point that you can bent it a little bit.
You put it on a rack and pull down on the string with the number of lbs that you want your bow to have. It will not bend much and it will not bend in a nice curve like you want so ..
You remove wood from the belly until both sides bend the same way but don't increase the amount they bend, just make them the same.
Now you start removing wood. As you do so it will bend more and more. Make sure that it bends the way you want by removing wood from the right places. Keep it symmetrical (unless that is not your goal tiller)!
NEVER pull with more lbs than you want you bow to be! This will over stress the wood resulting in all sorts of different problems.
Once it bends as many inches as your desired draw length, you are done.
I think a pyramid bow is a good place to start but that might be wrong.
Read the the bowyer's bibles, all four, cover to cover before you start!
What is the rule? Double the width and you increase the bows power 2 times. Increase the thickness and you increase the bows power 8 times?
There seem to be two basic tiller types, D and circle.
Forget recurves and such until you have done a few bows.
English longbows have a special shape that is not like the rest of the world's bow because they had special needs at the time it was invented.
Hope this helps.
Douglas E Knapp