What advantage is there in multiple laminations?

[markinengland]

I just got back from the Batsford shoot. Brilliant event and amzing to see a longbow shot of 450 yards! I wasn't feeling too well and missed out on the opportunity for some good bow making talk in the beer tent. While I can make a bow, it seems I can't cook without poisoning myself! I thought I would try and have a discussion here that I missed out on the other night.
While at Batsford I saw some nice war bows. Some lovely self bows, some laminated bows. As access to good wood for self bows is limited for many bowyers and customers laminated bows are becoming increasingly popular. Some of these laminated bows had five or more laminations, some three, some just a belly and backing.
I wonder what the performance advantages of any more than two laminations are?
Thoughts?
Mark in England

[grantmac]

From my somewhat limited knowledge: the idea is to have the backing being very tension strong, the core(s) as light and strong in shear as possible and the belly very compression strong. Usually compression strong wood is very heavy, so you want to have as little of it as possible to keep the bow light. The core just acts as a shear-web to space the belly away from the back.
That said I might be totally off, I also don't see the point of more than 3 laminations except for a different look.
      Cheers,
             Grant

[stevesjem]

I just got back from the Batsford shoot. Brilliant event and amzing to see a longbow shot of 450 yards! I wasn't feeling too well and missed out on the opportunity for some good bow making talk in the beer tent. While I can make a bow, it seems I can't cook without poisoning myself! I thought I would try and have a discussion here that I missed out on the other night.
While at Batsford I saw some nice war bows. Some lovely self bows, some laminated bows. As access to good wood for self bows is limited for many bowyers and customers laminated bows are becoming increasingly popular. Some of these laminated bows had five or more laminations, some three, some just a belly and backing.
I wonder what the performance advantages of any more than two laminations are?
Thoughts?
Mark in England

That was Jeremy Spencer' s flight shot of 432yds

Cheers

Steve

[markinengland]

Thanks Steve, I only added 18 yards!
Grant.
I think very much as you do. Tension work is largely done at the surface of the back, compression largely at the surfce of the belly. The middle or core of the bow essentially is non working and simply connects the working surfaces of front and back.
What I cannot understand is why some people put heavy timbers into the core.
Mark

[grantmac]

Mark:

I can't seem to understand the heavy core theory either. I just got my hands on some ERC and I think it will make a nearly ideal core wood. I can forsee a Hickory, ERC, Ipe ELB in my near future; not a warbow but something light and accurate for the backyard. The only way a heavy core would work is if it is very rigid wood, but even then it doesn't make sense. To me it seems like the core is mearly a shear-web which spaces the backing from the belly. A 5-lamination bow just seems to have a lot of glue, which doesn't really do any work and just adds weight.
I wonder what sort of lamination are setting these flight records?
    Cheers,
           Grant

[markinengland]

Grant,
Interestingly the longbow that recently set a new 432 yard distance was bamboo backed, Iroko core and Ipe belly. Iroko because it is failry light and stiff.
Mark in England

[backgardenbowyer]

My triple laminate field bow has hickory back (for tension) lemonwood belly (for compression) and the core is balau which I cut from a decking plank and is relatively light for a hard wood.  It's mass is 22ozs.  I'm just finishing a bow of very dense ipe backed with bamboo and at a similar length (though higher draw weight) it has a mass of 24ozs, and that's without the nocks and handle binding.  I'm thinking that yew would be a great core because of its light weight, whereas osage which I've seen used in the core of triple laminate bows would be poor because of its density.  Cedar sounds an interesting idea and they have some at our local wood yard, I did wonder about meranti - which is plentiful, sold as the generic light red coloured "hard wood" here and is really very low density for a hard wood its pinkinsh in colour and would look stunning with ipe.....maybe next time.

Does it matter if the grain of a core is flat ringed, edge ringed or bias ringed - anyone know?

Stan

[grantmac]

I'm not sure about most Cedars. I think the only one that is recommended for bows is Eastern Red, which is really a Juniper. I think Douglas Fir might be worth a try as well, I've got acess to tonnes of it so why not?
Aso for grain I think that it most likely doesn't matter, but it maybe more stiff with the rings in a vertical orientation.
     Cheers,
           Grant

[markinengland]

The intelligent use of a degree of Perry Reflex will reduce the mass of a bow for its draw weight quite considerably. This can be done with a bow with more than three toral lams, but apparently usually isn't. In my opinion, if all the thin lams are glued together all at once with no induced tension a massive performance advantage is lost, even if glued into reflex. If some of the lams are glued together into a whole belly and then forced into reflex when glued to the backing lams then Perry Reflex tensions will be built in and performance increased.
Stan,
Have you got TBB4 and read Steve Gardners chapter on bow mass? A hickory backed Ipe bow can outperform and weigh less than a self yew bow of the same draw weight.
Mark in England

[grantmac]

So your suggesting glueing up the belly and core then pulling them both into some reflex with the backing? You could go one further and glue-up the core and belly in a small amount of deflex, which is rather common with R/D designs. Then your added reflex would give you just enough tension for a small amount of resting reflex. I'm going to have to play around with this. I have a 66" 40-45lbs ELB in my mind, I want speed and stability. Of course this isn't the forum for that kind of girly stuff, so I'll set-about an 80lber at the same time.
       Cheers,
             Grant

[markinengland]

Grant,
I wouldn't want to give any secrets away but a naturally deflexed stave may give a real hooter of a bow if backed into reflex! I have that from a top nothc guy who is very well know in high performance wooden bows. Pleas wait until I have had a chance to try a delfexed backing and core pulled into slight relfex though!
Mark

[markinengland]

sorry, may have unintentionally misdirected you there. meant to say a relfexed belly/core glued into reflex wth a backing.
Mark

[grantmac]

So your saying a reflexed stave pulled into even more reflex with a backing?

[markinengland]

Grant,
No, a delfexed stave pulled straight or into a little reflex. By the time it is pulled back to it's original deflex a fair amount of work has been done, but the surface of the belly is completely unworked. This means the interior is working, perhaps largely at the glue line. A natrually deflexed stave pulled straight with a backing should act like a perry Reflexed bow. Small amount of reflex should make it still stable but act like a bow with a lot of reflex.
Makes sense to me.
This is the only way that mutliple laminations make sense to me.
Mark in England

[grantmac]

I think I'm gonna give that a try with a tri-lam. Laminate up the belly and core in deflex then reflex it slightly with the backing. If nothing else at least it shouldn't take much set and will look pretty.
     Cheers,
         Grant