Primitive Archer
Main Discussion Area => Bows => Topic started by: Philipp A on December 22, 2017, 09:25:03 pm
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Christmas Greetings from Canada,
I had this idea in my head for a while. I wanted to try a new style of bow that has a void each side mid limb. The idea was a further progression from an earlier bow where i tried to replicate the design of a turkey feather which has a deep groove on the back starting close from the base and fading out to the tip. I believe it allows for higher stresses similar to a double spar on an aircraft wing. I used it on a heavily crowned stave where I was afraid that I otherwise would break the bow on the back at the top of the ridge of the crown. It is actually a sweet shooting bow.
In any case I am 3/4 of the way finished with this experimental design and I am hopeful that I won't break it by the time I reach full draw. The two side limbs at the void are sloped at the belly to match the slope of the back of the bow. When drawing back I think I am getting some additional side deflection with the split limbs and I am hoping that I am storing some additional energy that way. The handle features a centre belly ridge and I will likely make the handle section a bit thinner yet to decrease the draw weight further and have it bend a bit more in the centre.
Here are the stats:
Wood: HHB stave seasoned for one year at < 9% moisture
Dimensions:
1) 67" n/n
2) 2.25" wide mid limb (including void)
3) each side limb at void 7/8"
4) width at handle: 1.25"
5) thickness from tip to void: 3/8"
6) thickness from void to handle: gradually increasing from 3/8" to 1/2"
7) thickness mid handle 3/4"
8) handle void transition concave at belly with belly ridge
9) voids transition with gentle slope to belly ridge and towards tip
10) tools used: bandsaw, hoof rasp, different files, drill to start voids and hand saw to cut voids
11) string FF with grey fox string silencers
I would love to hear what you think about it. I will post more pics once I reach full draw. I am aiming for a 70# draw weight.
I am posting the link to the google high res photos here and I am attaching a few low res photos with this posting (let me know if the link doesn't work):
https://photos.google.com/share/AF1QipNaeG7BrfDXdg1hoUTPVvfLC4V5CkcPhM1GoSRtngfe6z1pynOGlFYKPWe9voIqiw/photo/AF1QipPaknFtbUA-bO282TNrS1eRUZn4q0YzBzk7BAro?key=ZzRfWnliUGotN1VJZDNVWGk5TWlHZTc1T2VLODNB
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I think that it is really interesting and admire that there is some method to your madness besides looks. Generally speaking your energy storage is more a product of geometry that anything else. One place you might save a lot of energy or loose is in the vibrations at the end of the stroke. The majority of our energy losses come from limb distortion in the final few inches of power stroke and hysteresis. Seeing as how this is a sort of prototype I would back off the weight if it starts to take set and just try for as much as you can get.
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Hi Badger,
Thanks a bunch for your advice! I think you are right and I maybe should not finish it with a high draw weight. I will take it slow until I get to final draw weight and length. I will continue to long string tiller the bow in order to avoid set. It has worked well so far. The proof will be in the pudding when shooting it. I am not yet sure what to expect. I am intuitively thinking though, that the bow should shoot straight (if I don't wreck it before), since I believe the double voids and sloped sides at the void should give it additional torsional stability.
This bow took me a while to make and I hope I can keep it together without destroying it. At lease I have some photo memories in case i do :).
All the best, Phil
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Personally speaking - I think that pursuing a concept that you had and following it through with an actual creation is spectacular!! Folks like Badger can give you all of the technical details to make your bow as good as it can be, but going with a design that is a departure from the classic styles usually seen is the beauty of this pursuit.
If new ideas aren't developed there can be no advances. I love the utter simplicity of a "Plain Jane" flat bow, or a well crafted self recurve, but seeing someone really pushing the limits is exciting and keeps things "fresh" if you will. Basically, I think your bow is pretty darn cool!
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Although you have gone past what my feeble mind can absorb i agree that experimenting is never wrong.folks like you badger and others are what make this bow building thing so interesting ,wish you the best in your endeavor.
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Cool 8)
Del
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That groove in the quill of a feather adds two webs, which help prevent the quill from collapsing.. But the gain is only because the feather is hollow--the webs and the edge surfaces of the quill bear the entire load.
In the case of a wooden beam, any material removed from the compression surface reduces the strength. So, your concave section removes weight where there is no measurable gain by doing so, and reduces the strength, unless you make the limb as much wider as the width of the "void."
For a given width in a wooden limb, making the void WEAKENS the limb.
There is no magic.
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Very cool bow. Hope it works out for you.
In his book "Secrets Of The Omaha Bow" near the back, William Vonderhey shows a hickory selfbow he made that looks like 2 hickory poles attached at the handle and a few places along the limbs with voids between. I was amazed when I first got this book in 1992 that such a bow could be built. This bow is somewhat reminiscent of Vonderhey's bow.
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Thanks guys for all your encouragement and thoughts, it is much appreciated.
@ Jim Davis: I also appreciate your feedback and wanted to add some more colour to my post and see whether this makes sense to you. In regards to the turkey feathers when I dissect them the two "beams" on the back that are joined on the belly side have actually a rubber like mass inside of them and the end of the feather is the only thing that is hollow. So in reality I believe these feathers are a composite structure. I am not sure whether the function of the rubber like substance is to provide additional elasticity, I certainly would be interested in the answer since these feather are not just very flexible but also incredibly strong.
I agree that the void will have to be compensated by additional width which I have done (each side of the void the spars are 7/8" in width and I have carried through the void until the 7/8" width of each side meet up again towards the outer limb and the handle. I think that way I should not get a stress riser if I fade the void into the outer limb and the handle. One could argue I could have made due with just a narrower stave and gotten to the same place. That would be a fair point. I think though that what I have done might be a useful way to take care of a more heavily crowned stave without getting the extra stress in the centre portion on the back. By sloping the belly to match the slope of the back I am hoping that I again equalize the stresses over the width of both the back and the belly.
Whether I get any type of performance gain is still an outstanding question and at the end I might break this thing and it turns out an exercise in futility but in that case it sure was fun to make :)
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Hi Pat,
I forgot to reply to your post about the bow made by William Vonderhey, that is very interesting. Were there any type of further comments on it as to its performance and reasons for the design?
Carson Brown has told me that my bow reminded him of some illustrations he had seen once of some Egyptian bows. They had two square shaped limbs running parallel and then bound together at handle and tips, but free and unbound in the limb, so a similar concept. Maybe they did this just due to availability of suitable bow wood?
Cheers,
Phil
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Philipp, you are right a bout the quill being filled. That does prevent it from collapsing.
Since you have added width to compensate for the void, you have dealt with that concern.
As far as dealing with a high crown by making the void, that is an extreme version of a concave limb bow someone posted recently. This geometry does put another force, as you have mentioned, into springing the belly edges away from the center line. But I'm not convinced that energy is more efficiently stored there than in a conventional geometry. If it takes 25 pounds to move the limb tip 15 inches, 25 pounds is all you've got whether you have a flat plain limb or a concave limb or a limb with a void in it.
Lot's of us worry about a high crown lifting a splinter and breaking. But in fact, that almost never happens with a perfect growth ring end to end.
I made a toy indoor bow (don't look at the wall by the quilt rack!) that is about 3 feet long, 3/16" thick in the limbs and 3/4" wide at the fades. It has a 1/16" thick strip of hickory that is 3/8" wide end to end on the center line of the back of the bow. That little strip carries pretty much all of the tension forces and the bow flips a little blunt arrow out there hard enough to dent sheet rock (I ASKED you not to look at that wall!). I think the high-crowned back boogey man is not so scary as he seems.
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Hi Jim,
I hear you about the high crown concern, I did however break 3 HHB bows with heavy crowns without having violated any growth rings. These were also earlier bows of mine where my tillers were not much to write home about, so these more heavily crowned bows were likely even less forgiving if you had any resemblance of a hinge. Your indoor bow sounds like a lot of fun though. I am not sure whether I would be allowed to use one at my place. The dog would want to play catch and I would likely have to sleep in the dog house later if I make a hole into the dry wall :).
To be honest, I can try to rationalize my design all I want, at the end it is really just an idea I had and I wanted to see whether I manage to make it work. That question is of course still outstanding since I have not yet shot the bow. I still have a few small knots on the belly side (they don't go through to the back) that give me a bit of cause for concern and I am still wondering whether I should just work with them or carve / drill them out and fill them with HHB filings and 5 minute epoxy mix just like what I have done with a nasty knot on the belly side closer to the handle. They are just after the transition from the void to the outer solid limb a tricky spot for sure. Any advice would be appreciated!
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Philipp, if the knots are solid wood and tight, leave them. They are probably harder than the surrounding wood and will be fine.
Here is a picture of the back of that little bow I spoke of. The strip on the back does taper down at the ends to the width of the nocks.
Contrast is not so good in this photo.
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Hi Jim,
I see your point now that you shared a picture. Is it a board bow other than the strip? Thanks for sharing, I still think I should have one of those for my home to play with in the basement.
Cheers,
Phil
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Yes a "board" bow, though I cut the wood from a log, ripped it on a bandsaw and planed it to 1/8th thick myself. Board, but not from the BORG. :)
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Hey Jim, That's funny I think I saw one of these bows, on a Star Trek episode. Maybe it was from a Borg?
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Philip, spectacular looking bow!
I think that this design can only be done with special woods like HHB, Elm, or Hickory.
I studied the forces on this design, but I cannot see any advantage - maybe Steve's theory about vibration compensating.
I'm really curious how that bow will shoot. So thanks for doing the work and the interesting posting - keep us updated!
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Cool looking bow either way, hope it works out and shoots well for you. :)
Pappy
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Great experiment, and great bow!
Made me think of the bow of David A Jenkins, 2000AC. If I understand the concept correctly, it has holes in the limbs too. Claims a benefit of 10%! So there you go. Patent...http://www.google.com/patents/US6536421
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Interesting reading, Jan. especially the prior art and some of the patent citations.
Wonder how Philipp A's HHB Double Void Experimental Bow is coming along?
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Hi Jan,
Thanks for posting this, this appears to confirm that there is reason to my madness :). Most things that people come up with someone else has already thought of before. I certainly would have never thought checking any patents to see whether there is one similar to my bow design! Fortunately I am not into this hobby (more properly described as obsession) for commercial gain. The invention described by David Jenkins is indeed very similar to my bow. It doesn't appear though that he flared the voids into the tip and the handle and strangely he does not seem to keep the width of the side limbs the same throughout, but shows the slot as being straight. In my design I maintain the width at 7/8" throughout until the side limbs meet up towards the tip and the handle. However typically in patents they show only the stylized schematics without some of the details included, so his design at the end could look very similar to mine. I am curious wether David Jenkins has built any of these bows and whether there are any pictures on PA of the same. Do you know?
I am now almost finished tillering the bow and I will be likely shooting it before the year is out. I will post full draw pics as soon as I have shot the first few arrows and have finalized the tiller if satisfied with the results. The bow does draw pretty smoothly but is still too stiff for me. I am aiming for ~55-60# at my draw length of ~26".
Happy New Year,
Phil
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I don't think that bow ever made it to the point where anyone actually heard anything about it. I wonder if there are any working models floating around.
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Hi Badger,
I have looked Professor Jenkins up on the University of Florida website. He is a Professor of Engineering. I will contact him once I have finished the bow and get his input and see whether he has any pictures from the the similar bow design he has obtained a patent on. I am sure it will be an interesting discussion.
Happy New Year,
Phil
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The design like in the patent are sometimes called “shape shifters” because of how it uses the change in cross-section to change the stiffness of the limb as the bow is drawn. I’ve built a couple other variations a number of years ago. One was simply a top limb that twisted 90 degrees one way to the nock, and the bottom limb twisted 90 degrees the opposite direction. As the bow was drawn, the limbs straightened and it flattened out the force draw curve for the last part of the draw. It required very careful tillering.
Alan
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Allen, how was the performance?
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One of the problems with the bow in the patent is that it is very sensitive to grip pressure or slight tiller imbalance. One limb will tend to “break over” or flatten out suddenly before the other. It depends on how how deep a “V” the split limbs are made too. Greater shape-shifting effect is usually less stable between the top and bottom limb. This is probably why this design isn’t seen much.
Alan
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I didn’t really carry it much past half size working bows. It seemed to shoot pretty well, but I went another direction before takin get it to full size Flight bows. I was just surprised to see how it affected the force draw curve. It really takes a commitment, time, and energy to develop these things into something that works reliably.
I should still have one of these twisty bows laying around somewhere that I can take a picture of. The limb width was not tapered like a normal pyramid bow. Width was only trimmed from one side of the limb, the side that twisted to the bow belly. This approach seemed to work best and left the edge forming the bow back less violated. I made them from carefully planed wood with very uniform properties.
Alan
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@avcase,
how did your bow compare to my HHB double void bow from a design perspective? I have both sides to the void stay same width and I match the slope of the belly with the curvature of the crown on the back of the bow. I do flatten out the slopes as I get closer to the outer limb so I have a smooth transition to the flat portion.
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There’s was an article about that Florida Professor’s bow (Jenkins) published at least a dozen years ago. I may have a copy somewhere. I was playing around with designs at the time that had a U-shaped cross section that was supposed to flatten out but I think was extremely difficult to get to work reliably. I felt the Jenkins approach was better and might have some potential for a center-shot crossbow where the bending moments are identical on both limbs.
Alan
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@avcase,
I have found today this article from the University of Florida about Professor Jenkins' bow design. Is this the one you were referencing?
http://news.ufl.edu/archive/2004/04/uf-engineer-redesigns-classic-archery-bow-to-shoot-farther-easier.html
I will let you know how mine shoots once I hopefully get to the point of shooting a few arrows over the next couple of days. I still need to take a bit of draw weight off before I shoot it, hopefully I will get to it tomorrow morning.
All the best,
Phil
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Phil,
Yes, that’s the article! Wow, the internet never forgets. Haha!
Alan
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@avcase,
how did your bow compare to my HHB double void bow from a design perspective? I have both sides to the void stay same width and I match the slope of the belly with the curvature of the crown on the back of the bow. I do flatten out the slopes as I get closer to the outer limb so I have a smooth transition to the flat portion.
Phil,
Your bow is like the Jenkins design in cross-section in the hollowed out area of the limb? At first glance, I thought it was just a hollow space in the middle of the limb. I guess it depends on how thick the limb is compared to width. It looks like it is thick enough that it won’t flatten out much as it is drawn. Thin and wide will tend to flatten itself more as it is bent and will also be less stable.
Alan
Alan
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Hi Alan,
The cross section in the area with the voids have sloped sides towards the centre when viewed from the belly. The slopes match that of the crown of the stave on the back and the thickness does increase a bit towards the handle where the two sides come back together. It then transitions into a belly ridge on the handle. Towards the outer limb the slope flattens again to assure a smooth transition to the flat section of the outer limb. If you click on the google photo link at the beginning of my posting I have a whole bunch of pictures posted, with some of them closer up where you should clearly see the slope. I have some pictures of the bow on there as well when it was at an earlier stage (pre tillering) where I have not yet incorporated the sloped sides. Let me know if you want any more pics closer up when I am finished with the bow, I would be happy to post them.
Cheers,
Phil
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I can just see myself making a hundred of these things trying to get them to break over right. I am glad someone else is working on this one.
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I can just see myself making a hundred of these things trying to get them to break over right. I am glad someone else is working on this one.
I agree! It takes a lot of work to take a concept to a real working design. I used to spend a lot of time on different kinds of ideas. It can be a lot of fun, but it can be really time consuming and frustrating to get just right. Regardless, I do think it is healthy to try stepping out beyond the tried and true sometimes.
Alan
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for those who like to see, in the attachment is the same article, but with picture. Dont remember the origin.
Would be great to see the results Alan.
Could be worth trying to cut some slots in an old bow.
Jan
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Hi Jan,
I have clicked on your pdf file link but it contained zero bytes. Can you repost it?
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Hello Phill, seems to be a problem to post it from my present location!!! But you can find the file in my first post.
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Hi All,
I finally started shooting in the bow today and I am posting a couple of pics (they are not the best but it was minus 22 degrees Celsius when my son took them). I am now about 90% finished and I will continue to take some additional draw weight off the bow so I can fully draw it. It is currently 50# at 22". I think it will want to end up around 65# final draw weight @ 26". I have a maximum draw length of 26". I am concerned that the bow will get too thin if I try for less than that.
The bow actually shoots very nice and straight and has no hand shock. The bow weighs 606 grams / 21.4 oz and is almost exactly the same weight as the belly ridge bow I have made earlier this year which was also 67" n/n. I am using the same string for the bow. I forgot in my original post to add that I have been using two different scrapers in addition to the tools I listed to make the bow.
I have also added a pic that shows the slope of the side limbs in the section with the V slot. I did not experience any let off when drawing back the bow except that it didn't seem to stack quite as much as some of my other bows. I am still careful trying to find the limits of the bow since I have to get used to the way it draws. The pictures have also been added to the original google photo link if you want to view them in high res.
Happy New Year,
Phil
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Very nice execution and observations. Just now looking back at the "Haida Gwaii style bow" thread also, and I am reminded to not be so quick to dismiss some of the features seen on primitive bows that are not readily understandable.
The nuances that make one bow more usable or "sweeter" to shoot than another, can be somewhat subjective to the archer, and what we learn can just as well come from impressions that are difficult to prove in a scientific way. I hope you can share more opinions about what you are experiencing with your different limb designs.
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Thanks Willie for your words of encouragement, it makes the tinkering worthwhile :).
Happy New Year to you,
Phil
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Neat bow, interesting about the hand shock. Cool idea and well executed.
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The bow is looking nice so far, has it started to take set yet?
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Thanks @hoosierf, it is much appreciated!
@Badger: Yes the bow has taken so far net set of ~1/2". The stave itself had on the upper limb natural curvature about 6" from the tip and a hump as a result of a knot resulting in approximately 1/2" of curvature on the belly side. This lower limb had some natural reflex near the handle and some curvature belly side also ~ 6" from the tip. I believe I will end up with ~3/4" - 1" of net set once finished which is approximately where I am on my other HHB bows. So in short the double void design had no effect on set. I was careful to long string tiller it, but once the bow has been strung for a while and I had ~50 arrows fired it started to take a bit of set.
Maybe it has more to do in how I make my bows and maybe if I would aim for a lower draw weight (and not exceed that while tillering) before I start stringing them and shooting test arrows, I might be able to further cut down on set. I usually draw them to ~60# while tillering the bow since my HHB staves somehow want to end up between 60 - 70# @26". I have made one at 37# for my son's girl friend but found that the bows get awfully thin at those weights no matter how much I narrow the tips and I wanted to keep them somewhat robust so they can take a bit of abuse if that makes sense to you. But after reading about some of the speeds some of the people posting on here get with light draw weight bows I might need to reconsider my approach.
Any thoughts from you on this would be welcome!
Happy New Year,
Phil
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Just keep in mind that a thinner limb will bend to a tighter radius before taking set than a thicker one will. If you thin the limbs to reduce weight, you will not lose "robustness." If the limbs are already a good thickness (in your experience with HHB) then yes, it would be better to narrow them because you will get rid of more mass than by thinning.
I think you have a very visually appealing bow there. But I am sure the design adds nothing to performance. The extra edges of each limb at the void are extra places for the Poisson effect to step in. I know you left the limbs wider at the voids to make up for the missing wood, but there is no net gain of available energy storage area, so it will behave like any other bow with the same amount of wood in the same regions of the limbs.
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1" total set is not bad at all. I think you did great.
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Very much enjoyed watching this bow coming around - unique design really peaks the interest! Glad to see it casting arrows - hope it ends up where you're hoping for at your draw length.
Just one cool bow!
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jimdavis
But I'm not convinced that energy is more efficiently stored there than in a conventional geometry. If it takes 25 pounds to move the limb tip 15 inches, 25 pounds is all you've got whether you have a flat plain limb or a concave limb or a limb with a void in it.
and from your more recent post, you seem more sure than ever. Could you offer any support to your your opinion?
It seems to me that part of what is being investigated is how to do more with less, ie. make a limb that draws the same lbs with less mass? looking for increase in efficiency?
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@willie,
Other than having this visual image in my head for a while of how this bow could look, I think you are right in what my goal ultimately is with this bow. I wanted to make a less stacking bow that is comfortable to shoot, with less mass while maintaining or improving performance. I still have to take some additional draw weight off the bow to make a determination whether this is a better shooting bow when compared to my last bow (the Haida Gwaii style belly ridge bow). My first goal was to make this bow so it actually won't break when shooting it. So far I have at least achieved that part.
So keep tuned.... the jury is still out!
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I wanted to make a less stacking bow that is comfortable to shoot,
Yes, and that too. Easier on the shooter and easier on the arrow.
I guess there is more to efficiency than how much can be stored in a limb.
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It would be interesting to compare with a bow same wood same length same drawweight with flat or lenticular cross section.
Thank you for showing the experiments.
(@Philipp: the link you sent me is not working anymore :()