by Rizzar on Sat Aug 11, 2012 9:08 am
So, to be absolutely clear: the distance between the prod and the nut fingers is 12inch not 9 inch??
After re-reading the post I´m quite sure about this
(all calcs consider ~8mm on each end for string accomodation)
In this case with a brace height (included in 12") of 3 inch there would be a draw weight at about 270-280 lbs.
The steel (depends on exact type) would be near maximum suspense (safety included) if correctly handeled.
The calculation depends on a triangular shaped leaf-spring, but I dont think the measurements of your prod are all correct for an even distribution since the ends are going to be a bit thin. Some sources would say 16mm (40% of the middle) were optimum for even distribution in the whole prod. (Considering this aspect the formulas I use can not be 100% correct)
In your case I wouldn´t go to complete maximum tension for the prod. The thinner limbs should benefit in a greater speed (lower mass weight) a disadvantage of durability and a reduction of draw weight (edited) , so think about safety.
If you don´t make a deflex into the prod, the maximum draw would be ~24cm (9,45") at ~290#, if you exeed this (12" would be what I call exeeding) you´re going to get into trouble and I would prefer not to be in reach when you span it.
Another point is the string would be unter a certain tension the whole time and sring mounting would be quite hard, too.
Another interesting question, what kind of spanning device are you going to use?
Btw I like your tiller, but I would have preferred to glue the deck on the tiller, so you don´t have these screws all over.
Rizzar
Last edited by Rizzar on Sat Aug 11, 2012 10:09 am; edited 1 time in total