Draw length VS. prod length on wood prods

Hello y'all !

Quick question here for those used to wood prods. I tried to search the forum for an answer but couldn't quite find it so here goes. 

What would you guys consider to be a good (safe) proportion of draw length (counting brace + power stroke) vs. length of a wood prod NtN (hickory recurve style with a good sinew backing) ? 

I usually work in a 3 to 1 basis (prod being 3 times the draw length distance).

What do you guys thinks ?

3:1 seems about right to me, I like to keep the centre stiff for an inch or two each side of the stock, and I would also suggest that deflex is pretty much essential if you are going for a short prod and a high draw weight

An old medieval french manuscrit say that bows must be 2 times longer than the arrow + the handle... but they speak about bows and not crossbows.
that's the minimum for a correct draw weight (50-60lbs) and good wood - longbow style. If you want stronger bow, or less good wood, that's better you have longer bow. Also with english style longbow (D cross section) there is more stress on wood than flatbows (which can be shorter than 2x arrow/ draw length).

But I speak about selfbows, made by wood only. If you put sinew backing, you can clearly be shorter than 2x the draw length... it also depends of the thickness of the backing (generally 1/10 - 1/7  of bow thickness is good... more, you add weight without performance).

I don't know about how works hichory (I think it's good in tension, not sure in compression); but if your backing is much stronger on tension than the wood on compression, it can create compression lines which reduice bow preformances generally. 

A lot to say about this and no absolute reply, except : longer bow, less stress on wood, less risk to break.... better wood is the same... also flatter limbs... lighter bow... less stress if the bow is deflex than reflex...

Attention, with sinew, you'll certainly add a reflex to you bow. That's better you add this reflex to draw length for better consideration about bow length.

Thanks a lot for the explanation, I'll try to find some better wood for compression (since I don't have access to horn easily), I'll probably laminate with the hickory being the core, sinew backing and belly with ?? I don't know yet.

If you aren't going to use horn on the belly, just stick with the hickory.  Better yet, use maple for the core like many Asian bowyers did and do.  From a couple thousand years of R&D, there is simply NO wood that can come close to horn for compression, and you'd be wasting money to try.  Better to stick to simply sinew backed wood if you don't want to go with horn.

Ok thanks for the advice... I did see some nice gemsbock horns that are pretty affordable on ebay though... would a hickory or maple core, horn for belly and sinew backing sound good ?

Nothing wrong with sinew on hickory, makes a wicked fast bow
I strongly recommend spending a long while on the Primitive Archer forum

I don't know Hickory enough. it doesn't grow here in Belgium so I never use it. But it's considered as a good wood for bows. My thought was just that I only see hickory for backing (on laminated bows), so it generally means it's good on traction; but it doesn't mean it's bad on compression. Osage Orange is on of the best for belly side, but yew can be used too, black locust is generally good too.
But it's sure horn will always be better, but if you make your first test, better use wood.

It depends of the draw weight you desire, but if you make flat limbs, you'll have more chance to succeed, also make it a bit longer than 2X the draw length (less risk)... I advise you flax backing, because that's 5x faster to make even if that's a bit different. You just have to buy good flax string. you can also glue it with white wood glue (with sinew, you need collagen glue even if Titebond can works too). Plumbing hemp can be used too (I have less experience with that)... Dacron can be used as backing too.
the difference is more because you don't have the reflex effect of the sinew that contract itself. So when you glue other materials, that's better you bend your futur bow on reflex form during the gluing and let it come straight when glu is dry.

A 3/1 ratio is about right...I like a few inches of deflex, too. A longer prod (relatively) can handle higher draw weights, but will also need to be thicker, and physically heavier. Something between 30-36" long seems to work well; I'd wager a 300# draw is achievable on the long end.

Hickory is a bit weak in compression, prone to take a set; I'd design the prod a little wider with this wood than I might with say, Osage. No wood is going to handle anything like the forces that horn can, though...

Sinew will work better than plant fiber in this application, IMO; it will reduce stress on the belly compared to less-stretchy backings like linen. You'll also need to know how to deal with sinew if you end up making a horn/sinew prod.

Yes, if you want to make a 300lbs bow, I suppose you have to reduice risks with deflex and longer bow. that's logic even if it means loosing speed... hard to find the good solution between high risk to break - very efficent bow  and the less risk - stronger bow... for classical bows, draw weight is very important as that's the limits archer can use which determinate the bow. For crossbow, when you have something to help bending, the draw weight is maybe a bit less important.

Sinew is always better, sure... but I've already spent 5 hours hamerring sinew to make 1 chinese bow, and I know this isn't the most intereting thing to do, that's why flax is very faster.
Also I've always glued sinew with hide glue and the problem it doesn't resist to wet weather (it rains very often here). But I think some people use Titebond II to glue sinew.

Almost no one, who wants a bow to stay together, used Titebond on sinew.  It's just not elastic enough!! Almost all of the two dozen or more Asian Traditional bowyers I know do not use hide glue for sinew either.  Almost everyone uses what was traditionally used -- fish bladder glue for sinew to wood.  Hide glue works best for wood to wood joints, done with many thin layers to soak in and build up before finally binding two pieces together,

Flax is fine for backing and does give at least some increase in draw weight; and it is much cleaner to work with.  But it's no real substitute for sinew.

Flax is more for reinforcement, you can have shorter bows. Not sure it really add draw weight or just a few.

I remember an american bowyer who use Titebond with sinew, but I don't remember his name. For horn to wood/bamboo glue, Titebond III works very well. I've already tested.

I don't really see a difference between hide glue, fish or sinew glue. I mean they are all collagen, but certainly with different other composition. Both can glue sinew (which is made of a big part of collagen too). but the different composition can certainly have different effects.

I normally use Knox glue (basically the same as hide glue but made with little packs of knox gelatin...just less smelly) to apply sinew. So far, it has never let me down.

The only problem I get with my prods is that the bellies have a bad tendency to break. I know I used to try to get the highest possible draw weight but to be honest, although my prods were the good size (3:1), they were too thick and couldn't hold the compression (and hickory is not that good compression-wise).

Anyway, thanks guys for all of your comments !!

Dan -- you said "The only problem I get with my prods is that the bellies have a bad tendency to break.".  That's what horn does better than anything in the universe  -- work in compression to keep things from breaking.  Second best is regular bowyer's fiberglass strips.  I've seen  a couple sinew-backed, glass-bellied bows that worked really well.

I don't know how to apply horn for a crossbow prod to be honest. Do you know where I can look this up ? I did make some reserch to find horn and I found some Gemsbok horns on ebay that weren't too expensive.

I also try to stay "historical" as much as possible but maybe I could try fiberglass as well. What would you use for that, I mean, what kind of product ?

And thank you for your time Kenh ! Much appreciated !

Although the chances are the prods were too thick, you could also try hollowing them, or 'trapping' them - reducing the width of the belly so it is narrower than the back. As far as applying horn, it needs to be smoothed, reduced in thickness to one third of the total thickness of the bow and toothed like a saw blade (and so must the wood of the core). This produces a bow in the style of a horn and sinew archery bow. For a crossbow prod, search this site as there are several threads on the subject including one that is live at the moment

Historically, no bows were made with matching grooves in the wood and horn.  Absolutely none.  Look at the archeological record.  That concept is a product of post-1930s attempts to replicate bows. 

The thing is people think a wood-horn-sinew bow is made from wood and horn and sinew.  It's not!  It is really made of lots and lots and lots of natural glue with some wood and horn and sinew to give it a shape.  I have a friend who has been replicating composite bows for close to 30 years, and after some years of grooving wood & horn, abandoned the concept and just uses 'roughed up' flat surfaces with 10 or 20 or more primer coats of thinned glue on each piece before joining the pieces with a coat of thicker 'adhesive' glue that sticks the pieces together.

What kind of fiberglass strips?  Those made specifically for wood-fiberglass bow building -- a matrix of fiberglass strands covered with layers of epoxy resin.  You can buy individual strips from a number of archery supply places.

To stick to the topic of sinewed wood prods, I think there is a lot to be learned by building a few in this style before tackling a horn/sinew prod. While the draw weights can't be as powerful in wood (or the belly will be crushed, as you've found), the proportions and geometry will mostly carry over. Wood/sinew prods can be pretty fast-shooting, as well.

My most recent build pretty well maxes out the weight I can pull using a rope cocker, around 200#. If I do eventually try to build a horn/sinew prod, I figure I'll also need a spanning bench or crannequin to bend it.

I think Daniel, that's better to succeed in wood/sinew bows before trying composite. Also, traditional backed bows are straight or with recurve or little reflex... composite bows are interesting if you use a very high deflex or high draw weight, if not, backed bows will be more efficent than composite ones (because horn is denser than wood).

What are the draw weights of your bows that break on belly? Have you tried different wood species?  Do you cut trees or buy planks? We learn bow making by breaking bows... so if it doesn't work, it just means you have to find the good way to make them.
How does them break on belly? I mean bows rarelly break on belly, generally they have compression lines and then break on back.

Thought I'd post a pic of my most recent wood/sinew prod, since I had one handy (this bow is shooting now! I badly need to take final pics, but I keep fooling with various details, lol).

The prod itself is sinew-backed osage orange, 31" nock to nock, deflexed by about 2 1/2", and pulls about 200# at 10" (4" brace/6" power stroke), just a little under a 3/1 ratio. I suspect this is about the limit of draw weight for this size and style (although a longer prod might deal with a bit more, as I mentioned above). The prod developed one small compression fracture in the belly, near a knot, but it hasn't gotten worse, or caused any problems in use.

Oh ... great crossbow. what is the length of the tiller? 
I like the snake skin (even if I'm not sure that's really european medieval)

compression fractures are generally not a problem except if it create a hinge (local deflex). When wood "break" in compression, fibers compressed themselves which create a consolidation (reinforcement) of the belly at this part of the bow but it can take a set and the back can have more stress.

Thanks! The tiller is around the same length as the prod, about 32". I harvested many of the materials for this locally, including all the wood, and the bone for inlays. The rattlesnake was killed by my dad last summer; it's definitely not very medieval-authentic as a backing, but looks neat (IMO) and works great.

Actually, my prods were breaking beacause they were too thick, I see that now. The compression was just too much for the hickory to handle. I did make a pretty decent shooter that is about 160 lbs, 37,5" ntn, braced at about 3,5 inches with a power stroke of 9 inches (12,5 inches total draw length). It's a bit on the big size overall though. I think I've been obsessed with achieving high draw weight but not so anymore... I think it will solve my problem.  

To answer your question now, the prods I made were board prods (I selected the hickory plank at a store but it's straight grained, very beautiful). I only tries hickory so far. I'd love to try Osage but it's not available where I live and I don't wanna pay too much shipping rates since I live in Canada).I think I'll try some more wood prods backed with sinew then I'll try to add horn.

That's generally better to cut wood by yourself because you know where it grows (on shadow or not, near a river...). Trees that grow too fast (sun and water) have larger rings and are less good to make bows (except if you make them large and flat).
Also the position of the wood on the tree is important. that's better to choose wood that hasn't been stressed on compression during its growing (down side of a branch for example or part on compression because of wind). That's true especially for D cross sections and high weight bows.
That's why buying wood isn't the perfect solution except if you live in a land with a few available wood around.

In Canada, you can maybe find yew, but taxus canadesis stay very small I think, more like a bush than a tree, so not sure you'll find the good one. Maple can be used. But I don't know your trees at all.

Weaker compression wood can also be strengthen with heat treatment, even if it's long and I've only tried once (no real experience).

But, yes, wood have more limits than horn and steel for bows. but that's lighter, so you have better performances as other materials. I mean steel is so heavy (10x denser than wood) that you loose more energy to make move the mass of the bow limbs when you shoot than the mass of the bolt. With wood you loose a lot less of energy, so you can have the same performances with a lighter draw weight bow. Horn is twice denser than wood so that's a bit less good.

but yes, make your bow flat and you'll have less problems.
If you make a first bow and the second twice larger, the second will be twice stronger (draw weight) but there will have as much stress on both bows. If you make the second bow twice thicker, the second bow will be 8x stronger and the stress inside will be 8x stronger too... so flatter, better but you'll need more wood to make a strong bow if flat.

I know Canadian yew and you're right, it stays small and very curvy. Not a good candidate BUT, or maple trees are majestic beasts... I might be able to get some decent bows out of them (I heard birch is pretty good too). Next summer, I'll definetely go take a walk and get myself some staves to make bows and prods (maybe some tobacco pipes as well)  .

Thank you again for the good advices, I can see you're an experienced bowyer.