Hickory Kid's Longbow (aide memoire)

 I recently got some nice rough sawn Hickory from an old mate of mine (he'd bought up a load from someone who was shutting up shop many years ago), I hadn't done anything with it yet, then my mate JT asked if I had a light weight bow to suit an 11yr old lad (about 20-25# and 25"draw).
It seemed like a good opportunity to saw out a slat of Hickory and give it a try.
Unfortunately I didn't take any pics as I was in a rush to hand it over to JT who was going to finish sanding it and fit a leather grip.
I took it to the club and actually roved with it! I had to treat most marks as a par 2! But I was happy to be shooting something light as my left elbow has been giving me gyp (tennis elbow), I even tried it shooting one of JT's warbow arrows which flew surprisingly far!
Anyhow I got JT to take some measurements for future reference as I'm thinking of maybe trying a 35# Hickory flight bow.

Length 55" nock to nock, 25# @ 24" 
Bow width and thickness at; Nock: width: 10.5mm, depth 9.0mm Mid: width 20.3mm, depth11.2mm Ctr-width: 22.3mm, depth 17.3mm

Good Day at the Club

 I went to our Sunday rove, despite a stinking cold. I had a Yew stick bow to hand over, to replace a smashed 35# Yew primitive. I also collected the smashed one for a post mortem (I couldn't see any problem, other than it being in two pieces!). The stick bow, performed beautifully with arrows flying out with not even a hint of waggle.
I was given a couple of bottles of wine by another guy as a thank you for making him the "Robust Yew Primitive" with which he won his last 3D field shoot.
I wasn't up to shooting having had a flu jab and covid jab in my upper arms the day before, but I had a good natter with the guys, a tot of medicinal rum and I walked out to the first mark with them.
The weather was lovely and a breath of fresh air did me a power of good, knackered by the time I got home though!

Out of interest, I sawed a cross section of the failed bow, near where it broke. It shows rather nicely how deep the heat treating penetrates, how I'd maintained a fairly even thickness of sapwood, despite the heart/sap boundary not following a ring.

Arrow Speed Testing

 I finally got round to testing the reworked shoot through flight bow, (a Hickory Mollegabet, with heat treated Yew belly). It did 216 fps, but jarred my hand and elbow terribly. Investigation confirmed my theory that most hand shock is caused by an uncomfortable grip. Obviously the light flight arrow and high speed is a big factor too.
I've done some reshaping of the grip and ordered some 3mm neoprene foam sheet to pad out the grip, before re-testing. I think there is still a good 2 inches of draw to be had, so I'm optimistic about its performance.
Video of the speed testing here:-
https://www.youtube.com/watch?v=uICsUspyvO0
Video of the bow here:-
https://www.youtube.com/watch?v=tlnfIAbGhH0

More Boo Yew Ipe

 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.

Boo Yew Ipe Flight ELB draw weight estimation

I'm trying to build a flight bow, but the belly lamination will be an Ipe slat which is 4.5 mm thick and this doesn't leave a lot of material for tillering. 
So I'm tillering it as Boo Yew stave and trying to estimate how the extra 4.5 mm of Ipe will increase the draw weight. Just for ease of calculation I'm assuming the Ipe will be the same as the Yew (it is stronger in compression, but I'm just trying to get an estimate.

Currently the bow is 40# @ 17.5" which correlates to 61.7 @ 27" draw (short draw flight bow).
Mid limb thickness is 16mm. 16 cubed is 4096 (stiffness being proportional to the cube of the thickness)

If I add 4.5mm to the thickness this gives 20.5 which when cubed is 8615.
8615/4096 = 2.1 so adding 4.5mm would give 2.1 times the draw weight! 129#
Hmm, looks like I need to take more off the belly before glue up.
Trying to calculate an appropriate draw weight and length without the Ipe to give the desired final result with the Ipe is beyond me, so it's down to the old successive approximation. Keep doing a bit and re-calculating.
BTW. Target draw weight is somewhere between 60 and 80#, so I have some margin to play with.

I've done some more work, but this is all rather guesswork. Adding 4.5 mm (I'm calling it 4 to allow for finishing) won't give the same effect at the tips as at mid limb. Say the tip is 12mm thick an extra 4mm is making it 33% thicker whereas near the grip where it is say 20mm thick it's only adding 20%. I s'pose taking the mid limb thickness isn't too bad.
I've currently got it drawing 19" at 35# with a 15mm thickness mid limb, which is giving a finished estimate of 101# . Still a bit high, if I can get the estimate down to below 90, I think I'll go for glue up.

Test Shot with Miniature Ballista

 It was a pig to bind the string onto the stubby arms of the ballista, and having tied one end on, that arm had to be held under tension by wedging it against the frame with a screw driver. I managed to get it done and it works! I'm using temporary skeins of braided nylon cord, as the cat gut was too powerful.
Getting it working has revealed several design flaws, and I firmly believe that is is an apprentice piece* to demonstrate the metal working skills of it's maker, rather than being an exercise in building a working miniature ballista.
* Possibly by a gunmaker or crossbow maker.
https://www.youtube.com/watch?v=Jqg6Qp7p2ok

Miniature Ballista

 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 14^th 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
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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.