measuring from the crown of a stave

[walkabout]

i am working on my hickory staves, and in doing so ran into a snag. if given dimensions are for the overall intended stave, then one should measure from the crown of the belly right? i dont have calipers or any other way to do this, so i set my stave straight on its side, then placed a block of wood against the crown. i then took measurements from there. would these measurements be close to right as long as i was measuring from the block square to the front center of the back/crown?

[Osagetree]

Yes, as long as the bock is level with the back of the bow.

[walkabout]

thanks for the reply. i figured it would work, not very diferent from clamping it back down to a bench and measuring from there. i figured the most important thing is that the bow is set so whatever you are measuring from is truly square to the center of the back of the bow, which i made sure they were. i double checked with a clamp as a caliper to see and it was within 1/16" give or take.

[Loren Holland]

I am trying to figure out how to deal with this issue also.  I am learning how to scribe a thickness to work around knots. i use calipers, and have even used dutchwarbows trick of using a monkey wrench tightened to  one point and then slide down to the measure the next point.

so far i have only worked with very slightly crowned backs, but from reading TBB I understand that the more crowned the back is (works differently with different woods, because one wood over another might take the tension better) the more that only the crowned area does the work, and the lower portions of the back now do less work, which adds limb mass but no return of cast for the additional wood. Also the limb is not as strong because not all of the limb is distributing the tension.
 now for the other side of the limb, i usually try to  work bellys flat dsitrubute the compression evely and lessen set. i only round the edges enough to smooth them down and prevent splitting or breaking points. but on staves i will admit that i have worked down edges of the belly while tillering to produce a crown.
given this, i am asking those who work staves and have much more experiance than me...how do you judge proportions as you deal with more crowned backs.  how much wider do you have to make a limb, is there a ratio? coversely is there a ratio for the belly also, to prevent set.

[walkabout]

i believe much of that would depend on the profile of the limbs, the type of bow youre building etc. with hickory the flatbow seems to take advantage of hickorys properties, wide limbs doing most of the work and narrowing to tips to help keep mass down where it counts. the stave im working on has a pretty undulating crown on the back as it grew, so i simply started with given dimensions measured from the side square to the cut limb profile, not including the crown. i figure that during tillering ill be able to see the areas that the crown is causing it to be stiff and work those accordingly. i believe tbb4 had a great deal of explanation on the ratio to which certain areas of limbs take stress, and some thoughts as to what designs would allow the maker to produce bows which make the best use of this.  tbb vol4, pages116 on go into detail as to the layout of bows to best deal with stresses, it also speaks of bows which the authors made to test the theories and how they performed.

[Osagetree]

A scribe measure that I use for marking facet lines. Running the flat edge along the backing the point on the post leaves a nice mark the desired depth along the side of the stave