questions about yew

[stuckinthemud]

OK, so, I have roughed out a yew crossbow, based on proportions of a surviving heavy crossbow from the 13th century.  It has 2 inches of reflex, and is 2 1/4" (55mm) wide, 1.5" (40mm) thick.  Tapers are roughed in with width and thickness reducing at 1mm per inch.   If I could do anything with this, draw-weight would be somewhere above 800# draw weight at 10"draw.  I have removed most of the sapwood as I plan on using a layer or two of sinew.

First question, do I need to remove/reduce the reflex?

If yes, then should I boil it, steam it or use dry heat - it is fully seasoned being cut 4 years ago.

My feeling is that this is more bow than I can tiller, the most heavy bow I have done is about 130.  Would you run with it, or, take it down to a more manageable 250 to 300lb?

[DC]

How long is it? I'm having a tough time imagining even bending it. Bending it would be like lifting an engine. You could spend hours exercising it using a block and tackle

[stuckinthemud]

Really short, 34 inches, much shorter than other known examples which are between 40 and 50 inches long.  I'm thinking a car jack would be helpful, but realistically  I think I need to reduce thickness by 1/3

[Del the cat]

Dunno... but if it's going to be sinewed you are probably ok with the reflex.
I think the only way you'll find out is to build it, taking care to measure and document everything for the mk2
My guess is the thickness is way to much and could be reduced by 1/3 or maybe even 1/2.
I'd say you are better off building something much thinner and more manageable and then scaling up the results by the appropriate factors as you will get some good data, rather than building something that either breaks or can't be braced/drawn
Del

[stuckinthemud]

I pretty much agree, these crossbows are very very addictive.  The last one I built yielded a lot of really useful data and maybe I'll be more comfortable to go full fat with the next one. Taking 1/3 off seems a sensible way forward

[DC]

How about making a pyramid bow with a flat belly that you can bend and then just keep gluing on 1/8" laminations until you can't bend it, then back off one lam. If nothing else you could use up all your scrap yew

[Ringeck85]

I don't know if self yew crossbows ever got much above 300# range (but I am not a crossbow expert, so if anyone knows bettter feel free to chime in), but if you can get it heavier than that, by all means give it a go!  Sinew will help, too, at the very least for safety sake if that thing (the wood gods forbid) blows up!   

[stuckinthemud]

I'm not sure anyone knows what the medieval wood bows could do, thats what makes this so interesting.   

[bownarra]

Wood can take the same strain now as it could then. You only need to make a working model to find out. I personally wouldn't go much above say 200 - 250# with wood alone.
surely if you like making crossbows a composite would be in the works I'm contemplating making one myself, as heavy as I dare go, just for fun If properly made you won't have to worry about a composite breaking.

[Markus]

Perhaps something here.
https://m.youtube.com/watch?v=gaGCrv4LyUQ&feature=youtu.be

[stuckinthemud]

Thanks for the link Markus, it is one Ive seen before, I reckon the bow needs a bit of tuning, 150 yards of 386lbs seems a bit on the.low side.

A composite is in the works, nearly finished prepping all the horn plates, but the type I'm most interested in is the yew and sinew, its been almost totally ignored as a type by researchers and writers but certainly did exist, though maybe not as a munition grade weapon

[Badger]

With a 10-inch draw it would take about 600-lb to give you the power of a 50 lb bow I would go for about 200 pounds and maybe a 15-inch draw