question for glass bowyers

[don s]

i know with all wood laminated bows the back and belly choices can make a difference in performance. back you want tension strong wood and belly you want compression strong. BUT, with a glass bow. how critical is this? also, is there really a difference on what your core wood is? wouldn't the glass on both back and belly  cancel out the back or belly wood choice and it would be purely esthetics(with clear glass). when i say cancel, i mean for tension and compression. as far as core wood goes. what is the difference in performance between, lets say maple and boo. i picked those two because maple is sometimes a choice for an inexpensive bare bones get it done hunting bow and boo is usually offered for higher performance. is the difference really noticeable to an average joe? last question. if you built two identical bows. except that one had a core wood that was more dense than the other. would the dense wood bow turn out with a heavier draw weight? everyone is welcome to share their opinions. thats what trad gang is about. i would really like to hear from the guys who make or have made enough to have compared.
         don

[K30bowfisher]

You can use almost any wood as a thin veneer under glass and over stronger cores. From what I understand, Maple, Boo, Walnut are some of the best core woods. Other woods with mechanical properties similar to these make suitable core materials as well. Lots of great bows are built with maple cores, and lots of bows are still alive 50 years later with maple cores too. It is hard to argue with success.

Kenny M has a fantastic post on here somewhere where he built 4 identical bows with different cores to test for differences in performance. That post is a very good read and the tests were conducted very scientifically and repeatably. The long and short of it was there wasn't much diffference.

[don s]

thanks. i'll look for kenny Ms post.
                                    don

[don s]

i just read kennyms test bow post. very interesting. all bows were pretty close. if i ever make a glass bow again. i think i'll just stick with maple for the core wood and the back and belly wood choice will purely be for esthetics.
          don

[Dick in Seattle]

Kind of a chuckle here on the subject of core woods.  You can outsmart yourself trying to outguess the wood!  I decided to try something different on my current project (now under first coat of finish).  I decided to go for all walnut cores (3 lams) behind a thin bacote back.  The design was my "classic" with a lot of string follow and no shelf.  I "knew" the string follow usually costs a few pounds so I allowed a little extra stack for that.  Someone said walnut is liable to come in a little light, so I allowed a little extra stack for that.  I also wanted a bit more weight than my last one of this design, Bamboozle, so I allowed a little extra stack for that.  Now, we're not talking much extra... "jest a tech..." However, they all ganged up on me and went the same way, nothing actually would have come out light.  I was shooting for 35 and came up with 53!  Still came out a nice bow, just nothing near what I wanted.   Certainly nothing wrong with walnut cores, though!  Plus, they're beautiful... I'm used to the appearance of boo and maple.  The dark walnut is really different.  That's one of the nice thing about glass, you can play with all kinds of woods.

[JamesV]

I think the limb design is more important than the choice of limb material. Using the same form I have built glass bows with limb cores of, bamboo, maple, walnut, purpleheart, yellowheart and Ipe with very little difference in performance. The Ipe & purpleheart did come in a little heavy.

James...............

[ChristopherO]

This is a link to a thread I just posted last night concerning this subject.  I thought the same as you but was proven mistaken.

 http://tradgang.com/noncgi/ultimatebb.php?ubb=get_topic;f=125;t=005268

[Lee Robinson .]

Wood cores do matter...as does the material used in the fadeouts of the riser.

If I make two bows that have an identical stack total thickness, but

1. one with 0.030" carbon on the back side but not the very back as it is under a 0.030" glass backing
2. the other with 0.050 glass on the back and 0.010 more natural core

The carbon bow will come in WAY heavier. I have to reduce the core by 0.030-0.040" (depending upon pull weight and bow length) to get the same poundage as a non-carbon bow.

Additionally, I have seen some deep cored glass longbows take a set after many years of use. That wouldn't happen if the glass did all the work.

So, what this means to me is the core does matter.

Randy from Saxon Archery told me about 15 years ago that even though bamboo was so light, he had to use more core to get the same pull weight than if a limb had osage in it (which is heavy). Somewhat of a "rob Petter to pay Paul" situation in his opinion. Me personally...I have never had an laminated osage bow that I liked as they all had some degree of handshock...but I don't recall EVER handling an osage limbed bow that 1. was of a good design and 2. used the osage the way it should be used (not too much of it and putting it only on the belly). So I will have to try this one myself out some day in a well designed bow to see how it works when used properly (no more than 0.050" MAX and only on the belly).

Currently, I only offer bamboo and edge grain red elm as my cores (I do have some flat grain red elm as well) as both are PROVEN limb materials. I can use all one material or all the other, but many times I use a combo of them putting the bamboo on the back and the elm on the belly.

Maple and osage both are also proven limb materials with good compression, but they are heavier than bamboo and red elm. Of course maple is not a heavy wood, so I have no significant concerns about it and will in fact be making a maple "test" bow soon. I do however have some concerns on osage on the other hand as it is a considerably heavier wood...but I have to test it in a good design to see how it works when one uses it compression strength PROPERLY (not too much and only on the belly). Why someone would use osage in the shear or on the back is beyond me...as there are certainly better choices to use there.

This summer I am going to make up some "test bows" to check on variations in a final product that result from using different materials. The bows will all have bubinga selected in the longer fadeout section of my riser. They will be made to the same draw weight and the same riser and bow length. The CENTER (shear section) of the core does very little work and will be the same material as the lighter material that is used on the back-tension side). To prevent excess limb mass, when I use the maple it will be limited to no more than 0.060" (probably 0.050") while the osage will be limited to no more than 0.050" (probably 0.040").

The test will include 4 bows...

1. Bamboo back & core w/ edge grain red elm belly
2. Bamboo back & core w/ edge grain maple belly
3. Edge grain red elm back / edge grain maple belly
4. Bamboo back & core w/ osage belly

My hesitation is time. I won't have the time to do that until this summer. As a bowyer that has a scientific way of doing things and that seeks performance first...these are questions that I will not have satisfactory answers for unless I myself make these bows and do my own testing with them.

[highplains55]

protege has the right idea,glass thickness is the key and then core,my best longbows for less shock had yew cores with the glass belly trapped tillered,have had many hard rock maple cored bows work excl,i had a purpleheart cored bow that
was slow with avg. handshock, had a .030 glass back yew bow that would take a set if i left it strung overnight,so i trapped tillered it took off 5 lbs,and it shot better with less handshock.

[fujimo]

get hold of kennym
he built a bunch of identically designed bows, from different woods- he found no conclusive differences. it is an awesome thread- just search on kennym.

[**DONOTDELETE**]

This is a subject a guy could do R/D on till the cows come home on, and write a series of books while you are at it.

I've done extensive testing myself with different core materials, glass, and carbon backings. Not really all that much carbon though... The stuff is too spendy and dosen't burn well in the wood stove.

I agree that the core DOES matter.... but...unless you start thinning down your glass or carbon on deep core long bow limbs, it doesn't show up on testing as making much difference in performance.

For example: if you were building 60 pound deep core long bows using .030 glass belly and back, you would see a significant difference between an Action boo core, and hickory cores. If you build the same identical bow using .050 glass in the same weight, the difference would hardly noticeable.

i have found that keeping the "core to glass ratio" the same, helps in building the same length bow at different draw weights and still get the same performance level. For example, a 35 pound bow i use .030 glass. on a 60 pound bow i use .043-.045 glass and get very similar results.

getting back to core material.... in recurve bows with wider width profiles i think having a homogeneous core like bamboo is excellent. you are going to get more longevity out of this grass than you would using a dense hardwood too....

The total mass weight of the core stock used without using tomuch glass thickness or carbon, is where the biggest gains in performance are seen.

They use foam for core stock too and get away with it, but you won't see any deep foam long bows out there.... for good reason.... try putting belly carbon over foam some time and see what happens.     yup... the core DOES matter.... sometimes

[GREG IN MALAD]

Kirk,
How much velocity difference is there between bamboo and osage cores? I can feel the difference when shooting, but without a shooting machine I cant see or chronograph any. I like to keep things simple so I use maple for cores.

[Dmaxshawn]

Originally posted by GREG IN MALAD:
Kirk,
How much velocity difference is there between bamboo and osage cores? I can feel the difference when shooting, but without a shooting machine I cant see or chronograph any. I like to keep things simple so I use maple for cores.

Kenny did all these test last summer with 5 or 6 different core woods and all the same weights as close as possible to 50 pounds.  Let me see if I can dig it up.  

Shawn

[**DONOTDELETE**]

Originally posted by Dmaxshawn:
 

Originally posted by GREG IN MALAD:
Kirk,
How much velocity difference is there between bamboo and osage cores? I can feel the difference when shooting, but without a shooting machine I cant see or chronograph any. I like to keep things simple so I use maple for cores.

Kenny did all these test last summer with 5 or 6 different core woods and all the same weights as close as possible to 50 pounds.  Let me see if I can dig it up.  


Shawn [/b]

The actual Velocity is going to change depending on many things. the thickness of the core lams using osage vs bamboo, the location of said lams in the stack, and the thickness of the glass, or Glass to core ratio, location of working limb, all makes a difference.  the shear mass weight is going to be heavier using osage i would think.... osage wouldn't be a good choice for a glass bow IMO unless they were thin skins under clear glass for looks.

[**DONOTDELETE**]

btw.... Hey Dick... that walnut makes great core wood. espeacially the lighter colored sap wood. it's light weight and stiff properties make a great core wood.... the thickness of the stack pretty much determines the actual draw weight, but every time you change different core stock completely, you are rolling the dice on weight....    

[don s]

hey guys here is the test by kennym. if you read the second post this was suggested then by k30bowfisher. it's what i was looking for when i posted this topic.
                  don  http://tradgang.com/noncgi/ultimatebb.php?ubb=get_topic;f=125;t=001491;p=1

[7 Lakes]

I hate to commit blasphamy right here on my favorite website but one day I'm going to build two bows:
1st.  Red Elm (a proven bow wood that is pretty much beyond dispute.)
2nd.  2 x 4 stud from Lowes

I'm going to build them the same dimensions and see what happens.

[kennym]

Mike,
I'm thinkin a doug fir stud will be good, but a whitewood not so great.

 Besides, it will gum up a 20.00 sanding belt!  :D

[7 Lakes]

Didn't think of that.  I have a couple of nice fir strips left over from a boat project.  

I just wanted to build one from the worst materials I can think of, just to see how it shoots and holds up.

[kennym]

I thought of catalpa once at an amish kiln when I picked a board up. Waaay light,but after reading a little about it, didn't have what I thought were the strength properties needed.