Yew Prod Finished

 I went back and forth doing steam corrects, first adding deflex,  removing some of it, removing twist and generally trying to make it as symmetrical as possible so that I could judge the shape on the tiller. It's much harder to judge the curve on a short bow than a long one...obviously if you peer down an arrow shaft you can see if it's straight, but you see so well if it 's only 6" long!
I haven't had it back on the tiller yet since the last correction, but I'll add a pic and some figures for draw length and weight later. I have had it to 100# @16" before that. But with a crossbow you have to make allowance for an inch or so to actually cock the latch/trigger mechanism. So a 14" draw would probably be safe.
Here are some dimensions for reference.
Yew Prod, 39 1/2" nock to nock
Dimensions in mm, to 1 decimal place
Centre      37.6 x 14.5
4" along   35.1 x 21.0
8"             34.2 x 20.7
12"           31.6 x 17.3
16"           26.8 x 15.7
18"           24.1 x 14.5 :- note this measurement is only 2" from previous not 4" like the others.
The second pic shows the slight upsweep in the prod, this helps to lift the string line up level with the top of the track/stock/deck (whatever you like to call it), to minimise friction and string wear. It shows the nock overlay and stringer grooves nicely too.

  

It's finished now... here it is full draw 100# @ 15"

Yew Crossbow Prod

I had a guy from Holland contact me interested in a Yew crossbow prod so I've been looking at my Yew and I have several staves/billets that might be suitable.

I'm thinking a reasonable starting point might be about 36-40" long 12-13" draw length 100-120 pound draw weight ? 
I've started roughing one out to get an idea of what is required. It's rather an undulating stave and has a couple of knots on the belly that will need filling, but it's fine for a try out. I'll steam in some deflex, that will allow a longer draw length.
Wooden crossbow prods are a bit problematic as to get a decent high poundage and draw length you end up needing a rather long and unwieldy prod. Adding in deflex allows some extra draw length from a shorther prod. Without that you can end up with a very short power stroke and disappointing performance. The slight upward curve in the prod is to help get the tips up level with the track on which the bolt runs, this avoids too much downward string pressure and friction which looses power and wears the string.

There are several other posts on this blog about crossbows which go into some depth.
https://bowyersdiary.blogspot.com/2011/10/graingram-scales.html

https://bowyersdiary.blogspot.com/2011/10/detail-pics.html

Flight Bow Explosion and Flight Arrows

 Had a great time shooting on Sunday with JT and the Boyton cross chaps.
Testing a flight bow and a new arrow. The first couple of shots went well, and the new arrow was good (more about that later).
Next shot BANG and the bow disintegrated spectacularly. The entire flight bow build is on my Youtube channel and this first video shows the defect in the otherwise gorgeous log
Inspecting the debris and sawing through where the belly defect had been filled with a V shaped patch, showed a bit of a cavity at one end of the patch. Maybe that was the weakpoint where the break initiated. Studying the grain pattern in that cross section picture it looks as if the trunk may have originally been two limbs that grew together, it couldn't be seen from the outside. We never did find the nocks!

Back to the flight arrow!
This was the first flight arrow I'd made with the balance point slightly behind the geometric centre. Turkish flight arrows are like that and other accounts say it's a good thing. However I'd been put off trying it as I'd seen a wild arrow with the balance point behind centre fly extremely eratically, turning at right angles, diving and climbing and finally settling as it lost speed.
The new arrow had the balance point about 5mm behind centre and it flew fine. I think the difference between this and the wild arrow was the taper in the shaft (the wild one being virtually parallel).
My arrows are much thinner for about 1/3 of the length from the front. There are several ways of viewing what this does aerodynamically for stability. You can say the extra width at the back end is effectively like extra fletching, or the extra diameter increases drag at the back. Either way it helps stop the back end trying to go sideways. My thoughts about flight arrows are more qualitative that quantitative and are just my attempt to explain what and why makes a good arrow... you may dissagree and I'm not going to argue or attempt to defend my views. BUT, if someone finds them useful or though provoking, that's good.
I think the first 1/3 of a flight arrow (at the pointy end) is mostly there to stop the arrow falling off your hand or arrow shelf! Obviously that's a slight over simplification, but the bending forces early in the loose are relatively small as the arrow path is still fairly straight. The arrow only needs to bend round the bow as the string starts to get closer to the belly. You can test this youself by watching the sideways movement of the poit as you slowly let the arrow down from full draw. Or you can draw it out to scale and see how the angle of the arrow changes (All this assumes a bow that has the arrow pass about 1/2" off centre, ELBs etc).
Anyhow, the result of this is that you can have a nice stiff back end, a thin front end footed with a stiff heavy wood, a tiny point, small fletchings (say 2mm long 6mm high) and a balance point just behind centre. It should still fly well. It is virtually impossible to make an arrow that is sufficiently stiff but is too light. People will shout "Heresy", but you'll struggle to get below about 400 grains. People go on about 10 grains per pound (gpp) but that's nonsense other than for hunting arrows. 5gpp is no problem and I've gone much lower. Note bow poundage is no reliable indicator of accelleration on the arrow of launch speed. A 50# flight bow can out perform a 100# warbow and enven with "normal" bows a 70# doesn't shoot twice as fast as a 35#

Wonky Yew ELB virtually Finished

I've had it back to almost 28" on the tiller at
full brace, drawing 75#.
I took some pics to try and show a before and after shot. You can see there is a lot more deflex in the original stave. It needs a whisker mor work to get the right tip moving some more and maybejust left of mid limb (on the right).
It took several sessions of steam bending and dry heat treatment/bending to remove the excess deflex from the lower limb and make it relatively symmetrical.