Wood Prods

First topic message reminder :

Hi All,
I "carved" the beechwood down to about veneer thickness and it's still 'stiff as a board'.  That's okay because I've set it aside and a hazel stave is coming along nicely . . . I think; I'm nearly at the point of needing a tillering stick (has to be a milestone in the life of a crossbow builder).  I'm going to try, if it doesn't become too time consuming, to work in a wippe-like addition to it.  It will provide some measurements for when the time comes to make the one for the finished crossbow. 

Anyway, Mac, I'm looking forward to what you have to say about prod width vs. thickness; I think it will be an issue very soon - if not already. 

If anyone has experience with cutting new wood in the forest any thoughts would be much appreciated.
Godwin

Although I have posted them before, I will post here again what I have on the Berkhamsted bow.



Mac

mac wrote:brings us three more  wooden African crossbows.  The first one has more deflex than I think is good for it, and this may be the result of it having been left strung in some collection. 

This design is optimized to shoot light poison darts.
Ridiculously high brace height and almost non existent power stroke can in theory result up to 3 times the projectile speed of a low braced long drawn bow.

I remember seeing a TV-documentary about Cameroon hunters years ago. Their bolts looked really tiny and light, about pencil size.

Thank you!  That makes good sense.

As I collected more pics of the fang crossbows from Cameroon, it was becoming clear that the one was not an anomaly, and they pretty much all had that crazy amount of deflex.  

It's great to see how different Peoples have optimizes their bows for different things.

I think we can put the Cameroon crossbows and the Vietnamese crossbows at nearly opposite ends of the spectrum of how to make a wooden prod. 

Mac

epic!

This thread might be the most valuable on wood prods ever!

Here's another example, but it has been sadly chopped down.  The tiller is Quite long, and it must have been the sort of weapon that is used in a siege, rather than the open field.  The bow is very thick and deflexed.  From what is left,it looks like the limbs recurved a bit.  That is certainly a shape we sometimes see in contemporary illustrations. Unfortunately, we have no way of knowing how long the bow was in its working life.

It is also notable for having one of those push pin locks, rather than the more typical nut.  I am surprised to see that in what must have been a rather powerful weapon.



Mac

I have wondered about this bow... If we got a close-enough photo, do you suppose the front of the string-notch is reinforced with bone?  That's how I would do it.
Also, I believe the famous "Dresden" bow (mid 14th century?) which probably appears in Richter's book, maybe Alm's, apparently has a longish wooden prod, not reinforced with sinew or horn (an incidentally, the prod has been put in upside down and backwards and the nut is missing along with part of the left lockplate.  I wonder-does anybody have a pic they could share here online?  Geezer.

This is the best pic I could find of the lock.  It does not seem to be reenforced at all, but it's really hard to be sure.



Mac

Geezer wrote:
Also, I believe the famous "Dresden" bow (mid 14th century?) which probably appears in Richter's book, maybe Alm's, apparently has a longish wooden prod, not reinforced with sinew or horn (an incidentally, the prod has been put in upside down and backwards and the nut is missing along with part of the left lockplate.  I wonder-does anybody have a pic they could share here online?  Geezer.

Geezer,

Are you thinking of the bow in the City Museum in Cologne?  That one is definitely a horn bow, although it fits your description otherwise.

This pic from Harmuth shows it before restoration.



Mac

Yeah, that's the bow I was thinking of Koln, not Dresden.  But I seem to recall Holger Richter making some comment about a similar bow whose prod was really just wood.. maybe with a bit of sinew backing.  I'll take a look at my Hornbogen Armbrust book, no doubt it's in there somewhere... but such a booger to translate the German text to English.  Yeah, I know there are 'translation' programs available, but for this sort of technical jargon, they aren't always useful.
Geezer.

Ya' know...  If you have the computer wherewithal to get the text into a translation program, I would be delighted to collaborate on a project to make it be real English.

Mac

When I first became interested in crossbows I thought the only wood used for crossbow prods (and bows) are/were yew – but here in central Europe yew has been used to such an extent that it is now considered an endangered specie and illegal to cut.  With additional reading on the internet it seemed to me orange Osage and hickory are the American favorites.  Because of their popularity I suspect they are the best and at first I had the idea of importing one of them but the shipping costs alone would make me have to go back to work.  With yew, Osage and hickory being out of the picture I decided to look into what other woods are traditionally used and on the internet found a Czech bowyer whom I visited.
 
Mainly through him and some further study I have found the following woods are used – at least as hand bows: elm, hazel, ash, locust, black elder, hornbeam, yellow plum, and hawthorn and a couple more I can’t remember.  He had finished bows, some being worked, and some staves drying of several of the woods.  He gave me a couple pieces of hazel and a very short piece of yew.  (I’m working on the hazel now.)
 
Yesterday, despite his telling me winter is the best time to cut, I went into the forest a ways from where I live because I don’t want to wait ‘til winter.  But because spring is just beginning it was difficult to identify other species but with the help of my brother-in-law I was able to cut several pieces of hazel and one of hornbeam.  Closer to where I live I have spotted elm, black elder, and yellow plum; well, I have enough wood for now – but some dark winter night . . .
 
If anyone has worked with any of these woods, or has seasoned them I would really like to hear how you went about it!

I've worked several of those woods into bows, but from planks, not staves -- elm, ash, locust, and hornbeam -- from my experience all make really nice 'long' bows, and should make good prods as well.

Thanks, Kenh, that's really good to hear.  I'm always a little cautious with what I get off the internet and because of language problems I wasn't able to question the bowyer a lot about details.
Were the planks (commercially) kiln dried?

Godric,

It's never too soon to split your logs into staves.  The bigger the diameter of a piece of wood, the more it wants to check as it dries.  You want to get the wood down to sizes that can dry without checking.

Wood looses moisture fastest through its end grain. If left to its own devises, it will dry too fast at the ends and they will check almost without regard to how small the piece is.  Once a check starts, is will try to propagate into sound wood, so you need to do all you can to slow down loss of moisture through the cut ends.  Everyone agrees that they should be coated with something to seal them, but no two bowyers can agree on what's best.   Some say wax, some say pitch or tar, and others hold with glue or even paint.    I am willing to bet that within limits anything will do.  I have used wood glue, and I have used latex paint.  All things considered, paint is cheaper if you have some laying around anyway.  Slather it on well, and come back every now and again to put more on if checks are forming.

It's all about how the wood will shrink as it dries.


A log will try to split into wedges...  so you might as well start with wedges.  If they are small enough, and you keep the ends sealed, the stresses will not cause them to split any further.



Mac

I have seasoned rock elm and purple leaf plum. In fact I have a bunch of purple leaf plum seasoning in my shop right now. For the wood I have drying right now I just sealed the ends because I did not have time to work it down. This means it will take longer to dry out so it should be ready in a a year or two depending on the size of the branches. These were for hand bows. With the elm I debarked it, reduced it to a basic stave ready for floor tillering while still green, then I coated all of the cut surfaces with wood glue to slow drying and prevent checking. I did the same a purple leaf plum branch bow except I kept the bark on to serve as the back. Unfortunately it didn't make it through tillering (I had a new band saw and was too eager to try tillering with it, bad things happened to the poor plum stave). The elm took heat treating a little too well. I inadvertently made a really powerful recurve with it that I need to retiller to a lower weight bow. Elm is surprisingly robust wood to work with.

On the subject of bow woods, almost any hardwood and many softwoods can make a bow if you know how to handle them properly. Even non bow woods like pine and cedar can make a bow if you make them absurdly wide and or long. The Traditional Bowyers Bible series is a goldmine of information on this topic I would recommend volumes 1 and 4 for good information on both bow woods and (hand) bow design. They even have sections dealing with drying staves and lumberyard wood for bows. Most of my background has been making hand bows, I have little experience making wood prods so this thread has a ton of good info. I would love to see that Harmuth bow braced properly and at full draw. I was wondering if siyahs on a crossbow would work or be a hindrance.

Twedzel,

It sounds like you have a lot more wood bow experience than I do, so I am pleased to hear your contributions. 

That bow from Harmuth's book looks like this now....


....  It's a horn/wood/sinew composite with a very serious reflex.  It's had a hard life.  The sinew has almost all fallen off, and for years the bow had been mounted wrong way around.  If you look back to the Harmuth pic, you can see where some fool apparently tried to draw it that way, and one of the limbs was badly damaged where the "ear" starts.  

This is my "Dream Bow" and I count wooden prods as a stepping stone to get there. 

Andreas Bichler has made a very creditable crossbow based on it.  



...but we should try not to let this thread get derailed by composites.  They are a breed apart.  The rules that govern bows of homogeneous material like steel and wood just don't apply to them the same way.

Mac

This is all good stuff!  I’ve been reading on the internet and found what looks like a pretty good site by someone who shows and talks about the steps he’s taking (probably long ago as the thread was ’08, I think) with working with plum.
http://paleoplanet69529.yuku.com/topic/16421/Tutorial-On-Plum-Sapling-Bow#.VSaxCpM5tSp
 
After reading you folks on The Guild, looking thru’ internet sources including YouTube, I’ve come up with a plan (I’ll call it “Plan 1”).
 
One piece of hazel is large enough to split into two staves.  I will do that, chop out some of the wood on the belly side to get a basic prod shape, leave the bark on the back, paint the ends with latex, and where the wood was cut from the belly I will put on oil – probably just a vegetable oil or lard - to slow the bare wood side from drying so much faster than the bark side.  I will also put clamps on the center and the ends.  I read about that on the internet (maybe the above site) in an effort to prevent the ends from twisting.  I think it might be a good idea because the hazel I got from the Czech bowyer (cut this winter) had been bandsawed to the basic shape and worked on a little.  The end he had started had a slight twist.  I tho’t I had got rid of it with dry heat but it has returned and the end I worked on has developed one also.  I don’t know if it will prevent twist but someone said it helps?  I’ll let it sit for a few weeks with the other pieces (ends painted) while I finish the stave I’m working on.  Well, anyway that’s Plan 1 – if temptation doesn’t get me and I work on the new wood maybe just a little . . .
 
I’ll have the T. B. Bible tomorrow.
 
Please! - any ideas, comments would be greatly appreciated!
Godric

Its hard not to get sucked into composite bows when talking about all wood heavy weights. They are stellar in this category. I would love to make one as well but have no frugal access to the materials. It's on my bucket list as well. I hear they are very challenging to construct. But that bow is beautiful. I notice most modern fiberglass bows have much much less reflex than that one does. I wonder why?

I have tied both wood and bamboo down to a flat 2x4 while drying, I don't know how much it actually helped. They still needed a degree of straitening afterwards.

Solid fiberglass bows have a lot in common with wood bows in that the gross structure is the same from belly to back.   In both cases, we are using the same material in both the compression and the tension sides of the bow (as well as everything in between).  That material is fibers in a matrix, so strictly speaking it's a composite... but then again so is wood.

In a sense, we can think of "composite materials" and "composite structures".  The hornbow is a composite structure, one of the components of which is a composite material in the form of sinew in a glue matrix.

I think the reason we see more reflex on horn bows than fiberglass bows is that sinew can stand up to tremendous percents of elongation and still return elastically.  Glass just can't compare. 

If we think about solid fiberglass as a homogenous structure like wood, it's worth mentioning the the old Barnett prods are tillered very badly.  They work too much in the middle and not much at all in the outer limbs.  The result is that they always fail in the middle.  I have seen a couple of their 175#s go that way after only a few hundred cycles.  Their engineers aught to attend some remedial bowmaking classes.

Mac

Godric,

I'm not at all sure about the idea of putting oil on the stave to slow the drying.  I fear the the oil may soak in and alter the wood.  If I were going to put anything on I would want it to be something I could scrape off later. 

Anybody else have ideas on that?

The thing I see in the PaleoPlanet build along that frets me some is the amount of material the guy leaves for the string nocks.  Those pin nocks look just a bit undersized to me, and I think I would have gone a bit heavier there.  Also....  He has that bow bending a too much in the middle.  A bit more off of the limbs woudl have lowered the draw weight, but the result would have been more efficient and perhaps longer lived as well.

As to those limb twists.  I think you told me in a PM that they twisted in the same direction.  Is that right?  Small twists can probably be ignored in a relatively light bow, and twists in the same direction are better than a "propeller twist" for a crossbow.   Can you shoot some pics?

Mac

I didn't get that far along today due to spending most of the time trying to find pulleys.  I did get the ends painted with latex.  Tomorrow I'll do the splitting. Yes, the oil might not be a good idea - I haven't read anything about it yet in the TB Bible.  I'm just concerned about not being able to get to the new wood soon.
The clamping I will do - just small pieces of hard wood lath screwed to hold the stave at the center and ends to a plank.  Yes, the twists are in the same direction; I'll try to get some photos. It will be interesting to see if it helps prevent the twisting.  In the meantime, guys, back to the Bible . . .

Hi I'm new here and in need of some wisdom if you would be so kind, a friend has asked me to make a yew prod 26" wide with a 6-7" power stroke  and 180lb draw weight. I make a lot of yew longbows and understand the stresses and strains in making heavy war bows but then the draw length is considerably longer having done some maths I can't see how this prod idea can work at all let alone efficiently I know from research that wooden prods were used but perhaps I'm looking at this problem the wrong way? any help gratefully received

Hello and welcome to the forum, im curious about the math you did on such a small prod, could you explain it?, also, i think your friend is asking way to much from you, generally speaking wood is not a good prod material unless you make it pretty big and or wide, the way your friend seems to want the prod is like if it were a steel one and that doesn"t work, but if you want to force it, try to make it as wide as possible wich might be a bit hard since its yew, and does your friend want a selfprod? because i would definitely back it with something, also, you might try to make it a slacked braced bow in wich the string is not tense or tout until you draw the bow but you or your friend would need a special rail or stock to shoot it. If its going to be braced normally i would not brace it less than 2.75" or more than 3.5" but a wooden bow this size will take a big set.

26" prod of Yew or even Osage Orange, with that kind of draw weight and power stroke is pretty unreasonable.  Maybe a 36" or 38" prod...  maybe.  Wood-glass composite, sure, but not a self bow.

Thanks so much for your warm welcome and sound advice. you have pretty much confirmed my own thoughts on this.  my instinct tells me that it won't work and if you look at the math for a beam supported at both ends with a force applied in the centre for the given dimensions the maximum deflection likely is only just over 0.65 of an inch which makes sense after that you go beyond the tensile strength of the yew given as 11000kgf/m3. thanks again for your help. 

Tom