Tri-Lam Bow. Why?

[adb]

Of course it can!
You can't really compare a self bow with a laminate using boo and exotics, but, at the end of the day, it's the skill of the bowyer that counts.
It's just that a warbow is relatively more efficient when throwing heavy arrows than it is when throwing target ones.
I think you need to spell out what the 'myth' is, else I can't debate it... mind... I'm not sure I want to anyway, the history speaks for itself.

IMO The biggest Myth is that Warbows have a D profile... I don't think any of the MR Bows have what most people would think of as a D section.
Next!
Del

@ Toomany... nice post

The majority of the MR bows I saw had a D xsection.  Certainly, some of the heavier bows where a bit more square in xsection (or slab sided, as some people refer to them as), but certainly a rounded high crowned belly, with a flatter back.

[Del the cat]

They are more round in section or like an inflated square some are a bit like the letter "D" in this font (but with the sharp corners heavilly rounded so as to be almost circular) None are like the "high arched" D of a Victorian bow.
I've handled them and studied the cross section illustrations in Weapons of Warre.
If you disagree, we'll just have to differ on the point.
Which of the ones in the attachment do you call D section?
Del

[adb]

All the ones on the right appear as a D xsection to my eyes. Certainly round, but the back appears plainly in all the images, and can be determined by the fact that it's flatter.

[adb]

One thing I don't understand... how does all this advocating for a 'lighter' core wood apply to the mass principle??

I follow the mass principal, more or less. It makes sense. It takes less of a more dense material to make the same bow... design accordingly. So, if I'm making ELBs, regardless of material (including the core), and all else is equal, I want the bows to weigh the same when they're finished. Someone please explain. Marc?

[vinemaplebows]

The only reason I make a tri-lam is to use less belly wood - good clean yew slats are hard to come by.

Yep, or wanting to make a PERRY.

[toomanyknots]

One thing I don't understand... how does all this advocating for a 'lighter' core wood apply to the mass principle??

I follow the mass principal, more or less. It makes sense. It takes less of a more dense material to make the same bow... design accordingly. So, if I'm making ELBs, regardless of material (including the core), and all else is equal, I want the bows to weigh the same when they're finished. Someone please explain. Marc?

I remember reading somewhere I think where Steve said something along the lines of the mass theory needing to be tweeked a bit for longbows. Please don't quote me on that, if anyone knows what I am talking about or if I am wrong please correct me. Edit: Wait a min, I found it:

"ADB, the mass theory was more based on hunting weight bows, I have found on circular tillered bows it starts to wander off to the high side after about 70#, also as discussed in the book certain woods will tend to come in lighter, yew and cherry for instance. Your bow comes in at around 829 grams not allowing for yew wood if it is circular tillered. If I were to rewrite that chapter for heavier bows it would come in about 10% lighter. Tillering the bow for low set as you achieved will always overide predicted mass which is more of an estimated mass to arrive at close dementions anyway."

I think the woods that come in lighter would probably have better performance. I know using dense cores with dense bellys and dense backings does not give me the best performance, no matter how much glued in reflex they have or how careful I tiller them. And then there is beam theory, where by the result of having one tensile strain, and one compressive strain, there has to exist a neutral axis by default that is under no strain. If you taper your cores to reflect this neutral axis, in theory (which yes is incredibley different when comparing a steel beam to a bamboo/osage etc bow!, ) but still, in "theory" you should be able to fill this neutral axis with anything you want, given that it can take the sheer. So, in theroy, why not fill it with the least dense material that can take it? Although tapering does take a while on my end, I am using a 4 x 36 belt sander, which takes a while. I cut my lams 1/4 or more and taper the tips on the sander to less than 1/8", maybe 3/32". It is nice to just be able to glue up a bow with a 1/8" core without having to taper. If I was gluing up like 10 in a session, I would want to do 1/8" cores probably.

[Del the cat]

All the ones on the right appear as a D xsection to my eyes. Certainly round, but the back appears plainly in all the images, and can be determined by the fact that it's flatter.

Oh? Well there you go.
Yeah, the back can be "determined" but it is not glaringly obvious in any of 'em, as to my eye they are all fairly symmetrical about a horizontal axis, with the back being only very slightly flatter than the belly.
In fact the one lower right is flatter on it's right side than the back.
I'd have described them as being more like an inflated square or having slightly rounded bellies not at all like the Victorian D.
Obviously we have a different interpretation of the term and concept of D shaped.
I think I'll quit and go hide in my secret cat nest
Del

[PatM]

The bow on the right could be have the profile flipped the other way and be perfectly feasible as a crowned back and flatter belly.

[adb]

One thing I don't understand... how does all this advocating for a 'lighter' core wood apply to the mass principle??

I follow the mass principal, more or less. It makes sense. It takes less of a more dense material to make the same bow... design accordingly. So, if I'm making ELBs, regardless of material (including the core), and all else is equal, I want the bows to weigh the same when they're finished. Someone please explain. Marc?

I remember reading somewhere I think where Steve said something along the lines of the mass theory needing to be tweeked a bit for longbows. Please don't quote me on that, if anyone knows what I am talking about or if I am wrong please correct me. Edit: Wait a min, I found it:

"ADB, the mass theory was more based on hunting weight bows, I have found on circular tillered bows it starts to wander off to the high side after about 70#, also as discussed in the book certain woods will tend to come in lighter, yew and cherry for instance. Your bow comes in at around 829 grams not allowing for yew wood if it is circular tillered. If I were to rewrite that chapter for heavier bows it would come in about 10% lighter. Tillering the bow for low set as you achieved will always overide predicted mass which is more of an estimated mass to arrive at close dementions anyway."

I think the woods that come in lighter would probably have better performance. I know using dense cores with dense bellys and dense backings does not give me the best performance, no matter how much glued in reflex they have or how careful I tiller them. And then there is beam theory, where by the result of having one tensile strain, and one compressive strain, there has to exist a neutral axis by default that is under no strain. If you taper your cores to reflect this neutral axis, in theory (which yes is incredibley different when comparing a steel beam to a bamboo/osage etc bow!, ) but still, in "theory" you should be able to fill this neutral axis with anything you want, given that it can take the sheer. So, in theroy, why not fill it with the least dense material that can take it? Although tapering does take a while on my end, I am using a 4 x 36 belt sander, which takes a while. I cut my lams 1/4 or more and taper the tips on the sander to less than 1/8", maybe 3/32". It is nice to just be able to glue up a bow with a 1/8" core without having to taper. If I was gluing up like 10 in a session, I would want to do 1/8" cores probably.

I remember Steve talking about this before, and him mentioning it needing tweaking for warbow weight (70+#) ELB type bows. But, I'm talking target/hunting weight at around 50#. I just don't think that the core matters as much as some people think it does, especially if bows of different material are designed and tillered to have the same limb mass (in other words, following the mass principle). I think I'll continue to make tri-lam ELBs with compression strong core wood, and be very happy with them, and you'll likely continue to use maple as your favourite, and we'll both be very happy bow makers!

I think the only way to truly test this, and reveal any meaningful result, would be to make 2 ELBs... similar design, similar draw weight, same tiller and set, both with identical mass, and one made with a lighter tension strong core (like maple) and the other with a compression strong core like osage or ipe, and then wring them out for performance... cast, arrow speed at various arrow weights. I don't know, but I would guess their performance would be so close, you couldn't tell any difference.

[adb]

The bow on the right could be have the profile flipped the other way and be perfectly feasible as a crowned back and flatter belly.

Sure, it could be... but it's not.

[cdpbrewer]

Going back to arachnid’s questions on why to make a tri-lam since I have no experience with ELBs 
….
>  1) What are the pros and cons of a tri-lam vs. a double lam bow?

Gordon nailed the prime advantage of tri-lams over backed bows- they use much less expensive (or difficult to obtain) belly wood.  Some other advantages:

1.  The performance advantage is debatable, but I tend to think a tri-lam yields a faster bow than a backed bow.   Methinks this is due to a lighter bow when lighter core wood is used and, it’s said…. there’s another glue line for prestressing.  Whether a tri-lam is worth the additional effort in construction is even more debatable. 

2.  One can use the same form for glueing and the same bow profile and length and get wildly different bows by changing the taper and/or thickness  of the lams, changing the length of the power lam or tip wedges.   One can in theory get a bow that needs no or very little tillering- something I’ve not accomplished 

3.  A minor point but, compared with plain backed bows, they have less spring-back (or reflex loss) once removed from the form after glueing- especially if the belly of a backed bow isn’t pre-tillered.

4.  Some think they look cooler or whatever than a backed bow.   

Cons:  More labor intensive.  A thickness sander is just about a necessity.  Less belly wood for tillering,  More glue lines to fail if your glueing is sub-par (use Urac or it's replacement). 

2) Assuming I do want a tri-lam- are there any major design differences?

The major design difference is the core.   Of lessor import- tip wedges and the power lam.   

>  3) What are the  characteristics of a good core wood?

Lots of folks suggest maple as a core wood.  I agree.  I’ve not used it but elm is probably good also.   Elm and maple are what are used for inner lams in lots of bows surfaced with that unprimitive stuff we aren't supposed to mention herein.  Heck, foam is even being used  (albeit expensive hi-tech foam).   Which brings up a SWAG:  Methinks the core should be light and shear strong.   I tend to view a bow limb as a beam wherein most of the stresses are in the extreme fibers- i.e. the surfaces of the back and belly.  The catches are that a tri-lam’s limb is a composite beam and is prestressed when there’s reflex glued in or is otherwise “Perryed”.   www.bio.vu.nl/thb/users/kooi/#pijl  has some interesting but mind-numbing stuff on bow mechanics and composite bows.

c.d.

[toomanyknots]

3.  A minor point but, compared with plain backed bows, they have less spring-back (or reflex loss) once removed from the form after glueing- especially if the belly of a backed bow isn’t pre-tillered.

This is a good point too. Perhaps they tend to hold reflex better after being tillered and shot as well? Never actually thought about that myself. Now that I think about it, it seems to be true on my end.

[adb]

This is just my opinion, and I have no evidence to back it up, but... if done correctly (with good glue joints), I believe 3 laminations are stronger than 2. Much the same way plywood is stronger than lumber (I know it's a different process with plywood). I think whatever shape you glue into a multi-lam bow, the more likely it is to maintain that shape, even after being stressed. 

[Marc St Louis]

One would think that a multi-lam (complex composite) bow would have better performance but the flight shooting records don't support this theory.  The 50# simple composite record, a simple backed bow, stands at 326 yards.  The record for a complex composite (multi-lam bow) stands at 321 yards. 

[adb]

Interesting. Any details on the construction and materials of these bows?