Ah well, my calculations/estimates seem to be a bit too pessimistic, but better too strong than too weak! It's too stiff even after reducing the Ipe a little and rounding the belly. It was about 50# at 12" unbraced.
It was also trying to flip over sideways as it was rather thick compared to its width, also being unbraced and only pulling a few inches doesn't help.
I don't want to make the Ipe too thin, so I've carefully run it through the bandsaw down the middle of the thickest lamination and re-glues it. That takes about 1.5mm from the thickness.
Hopefully once it's finished I'll be able to work out some sort of fiddle factor for boo/Yew/Ipe.
I bought this from a "Fine English Sporting Guns and Rifles" auction. The attached label doesn't give much info, and the string is broken. I'm hoping to figure out how it works and get it going. It should provide many hours of fun. The trigger mechanism has virtually no wear on it, so I'm assuming it was made for the fun of it or as a demonstration of the workers skill. Probably Victorian?
The arms that the string attaches to look rather short to me and there is no obvious way to pre tension the skeins of sinew. The 'wings' can fold back or forth and this may provide a way of stringing and pre tensioning.
Here's a transcript of the info that came with it written on 2 tiny labels.
Text broken int 4 sections corresponding to the 4 sides
sides of the two labels. My comments in italics
Ballista/
Steel with folding “wings” :-
Origin and age not known, but animal-like sight looks oriental as does
decoration:-
Fitted with 14th century European pattern revolving nut; but the
groove in the stock is flat, not curved as in medieval bows to cut down
friction; if the bolt was flighted it would have to be less than ¾” across to
clear the columns in the central window (to be in scale the flights would be
about 5/8”
----
across, with 3 flights) ; Winding handle may be in Ivory but more likely in
Ivorine an early plastic;
Ones first impression is that it is French, the steel ‘stem of the handle’? is
half-heart shaped, elegant and ‘resolved’? ; Fixing wedge is oddly short and
undecorated; See ballistas on stands in Payne-Gallwey’s book “The Crossbow”;
bought from Terry Sovine (French name?) (address given but not shown here).
----
David Martin wonders whether the bow has been put on back to front; there are
two holes in the side of the frame towards the back which may be to fix the
crossbow to a stand. (I disagree); when strung the string slopes
downward from the centre; the screw thread on the screw holding the trigger
spring is approximately
----
1BA and the thread on the animal-like sight is 2BA- both are a bit sloppy so I
have locked them with Araldite; the barrel wobbles up and down a little; the
sight centres ones aim but is no help for trajectory; there are file marks
inside the outer wings and the centre ‘window’; catgut loose on right hand
claw.
This is my first successful bow of the year, 50# @28"
(an earlier Wych Elm primitive exploded after about a dozen shots! I shall be doing a "repair" and destruction test later, just to see how well linen binding supports a break).
The Yew was local to me, it had been felled by the council following some storm damage, and just left to rot.
The bow has some nice character is 66" from nock to nock, and the limbs are 2" wide at their widest.
Playlist for the entire build here:-
https://www.youtube.com/playlist?list=PLBz2tD9476KSe_bzPG5ZZRhW5_lEGsUWq
