Elasticity versus poundage

[BowEd]

Making another composite bow here.Going with less thickness of a core by 1/16" and more composites.Increasing the composites thicknesses.Thickness wise the dimensions of bow are all the same as the thicker core bow in the end yet.Close to same profile and length too.Same overall mass weight too.I'm wondering and will find out soon too after sinew cures how much overall poundage difference there might be between the two.With the wooden core being the stiffest component on a horn bow,and the horn and sinew being more elastic.Wonder what the difference if any the final result will be.Might be a pretty vague question to ask but just wondering if there are any thoughts about this out there.I'm using the same .70 density core material too.
I figure it to be a little more elastic.Maybe not as much poundage.If not I intend to just add more sinew.There's always that option I figure.I guess in a nut shell I'm asking how much value does a thicker core have in the poundage of a horn bow?Also does a more dense core if it is elastic enough to seem stronger?Wondering about durability here also.Even though it is in the neutral plane.

[gfugal]

If the bow is the same thickness, but greater ratio of composite material to wood, than theoretically it would be less poundage since the Sinew and Horn tend to be less stiff. but they are more elastic so it should be able to bend further and handle stress better. If it was already well within its limits then i would keep more wood. If you wanted higher poundage plus good stress capabilities maybe you should keep the same wood thickness but also inceease the amount of composite material, thus making it thicker than before.

[Stick Bender]

I have never made a composite bow but enjoy other peoples builds and working to  build one at some point but I enjoy Adams book so I was doing a little reading & here is my my interpretation for what it's worth & somebody can correct me if I'm wrong  but isn't the core material pretty much along the neutral plane and the vast majority of the tention & compretion work is handled by the horn & sinew so just Ruffly thinking wouldn't  it actualy bee more poundage with the increase in horn/sinew  I'm sure there is a better exsplanation but sence you brought it up it will be a good opportunity to learn !

[BowEd]

Good opposing analogies.Making bows sometimes goes against logic.I'l let it cure to find out.Thanks for the opinions.

[Aaron H]

My understanding is that the thicker core material is what gives you additional draw weight. Even though it is in that neutral plane, it still gives you the thickness required for a high draw weight

[BowEd]

Yes you may be right.You've been reading the new book you acquired Aaron?

[Aaron H]

Not yet, but I've still been doing some homework.    There's a composite in my future, just gotta get ready first

[BowEd]

Cool!!!Look forward to it.

[gfugal]

Now if you put Antler or Bone on the belly it should increase with poundge. Its stiffness is around 18 Gpa which is higher than most woods (surprisingly most Ipe is stiffer than most Bone) than it should increase the poundage for the same thickness. However, Bone/Antler isn't nearly as elastic as horn but it should be more elastic than most woods.

This is all theory, as i've never tried it myself. Redhand has built some antler bows and is doing a build along now. It sure is interesting and I would love to see more people test this out.

[BowEd]

Here's some eye pics of project.I'll post a different thread when finished.Pictures of the increased reflex as it goes.Goal with this one is to hit my draw weight at 28" maybe 29" after curing with very little tillering done.I'm sure some tweaking here and there will be required yet though.First after the horn was applied.


First sinewing done Feb.24,2017/390 grains

3 days later 2nd sinewing/565 grains

Around a week later the 3rd sinewing/around 200 grains

Around a week later the string removed for a bit already.I've noticed the sinew is able to pull on this one easier with the thinner core and a hint as to whether it will be the same draw weight.The sinew is soft yet though really and not cured.

A look at the back

Since I've put the stringer back on to fully cure.It's been a total of just over 3 weeks from first sinewing now.It's very smooth.Could of sized it once to show better[not a very good pic] but it looks like one matrix of sinew and glue already.The strands are'nt very distinguishable looking at it.

[BowEd]

Yes gfugal I think you are right.Bone and antler are stiffer but not as elastic though.Denser wood can be used too but not as elastic again.

[Stick Bender]

Hey Ed sense you used the same core wood on both  and I know you didn't tiller the core but what wood your ruff guess be on the core only draw weight  differences between the 2  I'm just curious I know it's not scientific but you have a good feel for weight ?

[Aaron H]

Very cool Ed, what is the core wood?  Did you groove the horn and core before glue up?  What glue did you use?

[gfugal]

That's some crazy reflex you have there  . I hope it strings good for you. It should bend pretty good if it has that much composite material. What draw are you going for?

[BowEd]

Ritch....Actually I tillered the core to brace...that's it... like the other.I want a nice even bend reflected when reverse bracing.The actual draw weight I could not say.It was'nt much that's for sure.Under 20#'s I'm sure @ 28".A hint of poundage would be to say it was 5/16" at the fade thickness and tapered from there.1/4" mid limb and so on.The previous one was 1/16" thicker overall and probably come closer to a 20# bow at 28".
Aaron H....The core is hickory again.Shagbark.Very thin ringed.No I did not groove the core or the horn on this one.To glue the horn onto the core I used smooth on epoxy...I know I know not hide glue???It can be used of course.Smooth on is not given it's proper due far as I'm concerned as far as taking a bend if put on thin enough but not dry jointed.Others have used it too in these profiles.Plus it cures within 24 hours too and is virtually bullet proof to enviornmental influences.It can be done also according to the directions on the can to be more heat resistant too.2 partsA to 1 partB then heat cured 2 hours@ 250 degrees will withstand temps up to 217 degrees F.The rest of the bow is sinew and hide glue.A pic as to how I applied the horn to core.

The horn is tapered first before glueing up.I  then heat bend the horn first to fit right up the fades to the belly of the handle first using a traced out profile of the curve transferred to a piece of pine.C clamped first then inner tube wrapped the rest of the way.It's best to wrap the bow with saran wrap first before wrapping with the inner tube to save your inner tube wrapping.I'm told and believe it to be true putting the horn on in a fairly flat profile especially these longer working limbs.Each limb might have around 14" working limb.So that the sheer forces are lateral along the limb.Reducing chances of delamination.These things I take their word for and sorta understand and so far nothing has come apart.
This bow is not going to be under the stress of reflex that a Turkish horn bow would be either but in the past I've tested these to be right up there performance wise.