Primitive Archer
Main Discussion Area => English Warbow => Topic started by: markinengland on May 26, 2008, 07:28:11 am
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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sorry, may have unintentionally misdirected you there. meant to say a relfexed belly/core glued into reflex wth a backing.
Mark
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So your saying a reflexed stave pulled into even more reflex with a backing?
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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
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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
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Mark, how about pulling the backing and core into reflex while glueing the two together. Then heating the belly and bending that to shape and finaly glueing them all together? I would think that would producs a bow with pre-stressed backing and core with a zero stressed belly. What do you think?
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Hang on Mark you were there? Now I hoped you would be did we meet? Userames are always confusing in the flesh as no one uses them!
For all those that weren't there the shoot was pretty special. Some bloody good shooting, good distances set and a very relawed atmosphere, even better than last year.
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Mark, how about pulling the backing and core into reflex while glueing the two together. Then heating the belly and bending that to shape and finaly glueing them all together? I would think that would producs a bow with pre-stressed backing and core with a zero stressed belly. What do you think?
I don't think that would work because the point is that the belly is under tension when the bow is resting and under virtually no stress when braced. I think that if you laminated the core and belly into what braced profile you wanted (and tillered it before glue-up), then pulled it into reflex you would end-up with a very low-stress design.
This gives me much to think on and I'm probably not a good enough boyer to properly execute any of it.
Cheers,
Grant
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i've been playing around alot with laminations the last couple months. .. One thing I have recently started to do, is glue up trilams this way:
First, the backing and the core together. When that has cured, I shape a riser to the curve of the stave and glue it in. When that has cured, I cut and sand in some fades, then glue a belly strip over that.
I wonder, if you were to glue the belly and core together, and then the backing to those like you have said in this post...would you omit the riser altogether?
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No riser on a warbow or elb, so it's a moot point.
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right, of course....
have you tried any douglas fir at all? I wonder how it'd go...god knows we have enough of it...as a carpenter, I know it as a very dense wood, but often full of hard knots and huge pitch pockets..at the Finishing Store around Topaz (off Blanshard) they sell 3/4" thick vertical grain douglas fir. might be worth a try...
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I don't cut to shape until everything is glued up. What I was attempting is that the backing and core would be pre-stressed into tension backwards on a perry reflex form when glued together while the belly would be heat shaped regularly into a perry reflex but make sure none of it is cut to shape before doing this, its all rectangular in shape from top to bottom. Then glue the core to the belly. The backing and core then cut to shape after its dried. The core and the backing will be pre-stressed in tension while the belly would would not. This way as you pull back on the bow your increasing the tension stresses and shifting the sheer points more into the belly (?) wood. Or is it that you would be making the core work for you instead of being just neutral? I would think the belly wood would take more compresion then if its not being made to take any tension but a full load of compresion.
What do you all think?
I have a couple lam ELB's going right now that I make by just gluing on a backing strip of hick to a thick peice of hardwood. Then I just cut out the shape and round over the corners and I'm about done. Power tools sure would make this go faster!
David T
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right, of course....
have you tried any douglas fir at all? I wonder how it'd go...god knows we have enough of it...as a carpenter, I know it as a very dense wood, but often full of hard knots and huge pitch pockets..at the Finishing Store around Topaz (off Blanshard) they sell 3/4" thick vertical grain douglas fir. might be worth a try...
I really want to try Fir. It seems like it would make a pretty awesome core to me. I've been playing with this Eastern Red Cedar lately, it's very nice but a real pain to find any without masssive knots. I'll be going back to Westwind to get another board in the next month I think. A local solution (fir) would be great.
Cheers,
Grant
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i have a bunch of maple lams and yew lams...but when the maple runs out (i have way more yew than maple) i will pick up some clear d-fir and i will let you know...
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David,
Pre-stressing the backing works. I know a respected bowyer who glues two thin hickory lams into a circle and then pulls them down onto the belly. This induces relfex in the glued together bow, though I am not sure there is any advantage compaired to just glueing a thick backing onto a thick belly and pulling it into Perry Reflex to dry. Different method, same effect.
I think you would get a better performance pulling the belly into reflex rather than heating it. The whole idea is to induce reverse stress into the bow. Heating gives shape but not stress.
Imagine this wince inducing experiments. Glue together and pull a two or three lam bow into reverse full draw shape and let it set. When it comes out the form it will look like a reverse bow. If it were possible to pull this reverse bow on a long string to straight you would have something like full draw poundage, when the bow is straight. Because the bow was pulled into relfex the surfaces of the belly and back are at zero stress as they ae now back in their original positions, but we have full draw strength locked into the glue lines. Of course this is a silly example but it illustrates the point. I once had a skinny Ipe bow with hickory backing made with too much reflex of 5 or 7 inches or so. It was pulling 120lbs to get the tips three inches behind the handle!
This kind of Perry Reflex increases the power of the bow compared against mass whle actually decreasing the stress at belly and back that usually cause failure. Taken to extremes you can see that failure could now be moved to where the stress has gone, which is the glue line. Some light wood may tear apart if used as a core, but only experimentation will tell you where the limits are.
Oddly, Perry Reflex works best on thicker lams and very little on a bow made of many thin lams. This is why I question the point of many thin lams unless the thin lams are glued up to make thick ones before inducing Pery effects (but why bother if two simple lams works so well anyway?).
According to Dan Perry, the best possible effect is to pre shape, round etc the belly and pretiller it to partial draw a little over brace height. Now glue on a backing and pull into reflex. You should get about 10lbs added strength for the backing and about 10lbs added strength per inch of relfex. This allow you to make a bow that at brace height pulls the same as a bow 30lbs lighter than you want, put the backing on, glue in two inches of reflex and come out the form bang on the weight you want. Ideally you should not have to cut any wood off after the glue up. Cutting wood off is cutting valuable pre-stressed wood off. You only have to see how reflex increases when you take wood off the belly and how quickly reflex drops with a light sanding or rounding off the corners of the backing so see that wood removal is changing the stresses. I match the back to the belly as much as possible, round the corners etc so all I have to do is lightly sand the joints at the sides. This has given me the best bows I have made so far.
Birch should make a good core. It is quite light for it's stiffness.
Nick, I was lurking at Batsford. I have a strange ability to hide in the foreground! Trouble with these forums is that even after you have met people in the flesh you don't know you have.
Mark in England
Mark in England