One thing about making an elb is that you are locked into certain parameters of a ratio width to thickness. If you want the bow 72" long just make it 1 1/8 wide. If it has too much mass at that length jst make the tiller more elyptical, f it is a very light wood like say cherry make the tiller rounder or full circle tiller. You can rough the bow out till it is bending pretty good but still heavy and then decide on the tiller you need based on the mass weight of the bow. for 72" long and 45#@28 you should use a full circle tiller between about 12 to 14 oz mass weight, a slightly elyptical tiller betwen 14 and 17 and very elyptical 17 to 19 oz.