Primitive Archer

this quote from Badger is from another thread, but I have found his observations  about wider limbs
interesting

Quote from: Badger on April 14, 2020, 12:42:02 pm

   I did some tests a few years ago on exceptionally wide osage bows. The results kind of disagreed with my own mass theory.  I built several osage flat bows with stiff handles at about 2" wide to 2 1/4 inches wide. To my surprise the mass came in slightly lower than the 1  1/2" bows. I use to build all my 50# osage bows at about 1 1/8 wide to about 1 1/4 wide. I found I got less set when going wider and I also was adding mass but they were still better performers because of less set. When I bumped them up even wider I fully expected to see a substantial increase in mass but it didn't happen. The bows came out much thinner than I would have expected also. The only way this is possible is if at 1 1/2" wide I was still doing more damage to the wood than I thought I was.

Mass itself has very little to do with a bow in my opinion. Of course where mass is located is important, but mass is a function of, not a design feature of a bow.

Mass is only a biproduct of the bows width and thickness. Its width determines the stress it can take and its thickness determines how much it can bend before taking set. The combination of those two individual design parameters are what gives a bow its mass. Applied incorrectly, you can get a bow the correct mass bit not the correct draw weight the mass is supposed to give. The entire idea of chasing mass is not going to get anyone anywhere.

The stress of compression is spread out iver surface area, the stress of tension likewise. You need the correct surface area for the draw weight of the bow, and the correct thickness for the bend radius. The stresses are not distributed across the mass.

So the question is, how wide and long does a bow need to be to not take set. The formula I have been working on is an attempt to solve that issue.Im about 80% certain i have it figured out, but without more bows of many different wood species built, i wont be 100%.  Its a simple formula The specific gravity is used along with the draw weight and from there you get how many sq inches of working limb you need. Soon as I know i am not putting out bad info, ill make a phone app that lets you put in your desired bow stats and it will tell you what you need to build.

a wide pyramid profile bow that uses levers at the tips

I hate quoting myself, but I realized this may be ambiguous. The pyramid profile I am talking about is not a straight taper from fades to the nock, the sides of the bow are convex and curved outwards a bit from straight. The levers happen because the ideal pyramid profile tapers to a sharp point at the nocks, but this is physically impossible because we need material for the nocks. So the profile shape is drawn to a sharp point at the nock, then a width for the nock is chosen and that width carries in towards the grip until it crosses the profile shape. If that is unclear I can make a sketch to illustrate better.

I feel more shock in the reflex thru out the length of the bow.

That's an interesting observation, Arvin. If you look at fibreglass recurves the limb bend tends to have the nocks move more vertically than horizontally. This seems to reduce shock and vibration. Some of the FG bowyers think this is because the limb mass is moving vertically, so the forces tend to cancel out between the top and bottom limb and it helps stop the limbs more quickly.

I have no idea if their theory is correct or not, but when you only reflex the tips it does the same thing to the limb bend and tip path as the FG recurves, just to a lesser extent.


Mark

Well, I already backed it with pronghorn rawhide (which, by the way, makes a FANTASTIC bow backing if you can get it), so I think I'll just leave it be.  But for future projects?  I've learned a lot from your comments.  Thanks, everybody.

If you go the route of sinew I would re tiller the inner a bit more to bend more then they are.  I would go with two layers as well on this one.  I think this bow would do quite well with sinew.  Just make sure you use multiple size coats to get good adhesion on the back.  The benefits of sinew are not just more draw length.  If done right it will add draw weight too.  If you are happy with where this bow pulls to now as far as length and weight then leave it alone.  If you would like a bit more out of it and “bulletproof” it so to speak then slap some sinew on it.  I’ve done this and it works great.  The shape and tiller of your bow is good now so it’s a good candidate for sinew.  A little more bend on the inners would be good.  Be careful not to add too much sinew so that it over powers the wood core and belly.  I’ve done this as well sadly.  For this little bow I would not add more then 2 layers and keep it under 60grams total.  So 30 grams per limb.  This will add a little and not be a net negative by adding more unnecessary mass to slow it down.   Looking at the shape of this now I would layer with 2 layers.  First layer consisting of 2 medium length measured bundles of 10grams each laid down from middle of handle out past the fades into bending portion of the limbs.  The next layer after a couple weeks of drying would be 2 longer bundles of 15grams each overlapping about an inch or so of the end of first layers on each limb out towards the tips.  I I would not lay much sinew at all out at the tips probably about 3-4” short of it.  Once that layer gels I would lay a little tiny 5gram layer overlapping the where the first two layer overlap feathering back towards handle.  All of these bundles very clean and thoroughly washed and combed before layer soaked in hide glue.  I would then cover this with goat skin parchment after a few weeks or more and this little bow would be a smoker!   With those short little non working recurves it would be really good actually.  Just my opinion on how I would likely go with this little bow if I was wanting a little more out of it.  Anyway if you want advise on starting out on this there’s lots of guys here that are old hats at this that I’ve benefited from too.  Dive in!  The water nice.   😊

I just roughed out a Meare Heath  designed bow that was found in the pete bogs of England that was made roughly 2600 years BC according to experts. It was a broken  bow that contained part of the handle ,and one limb. It is 75 inches long, 2, and half inches wide most of the length of the limbs, and tapers at the tips. The real deal was made with English yew. I used black locust, because it is what I had at hand. If I would have had a good piece of birch that would be what I would have used because of it's light mass. The rough cut bow is currently drying. I went to Utube, and saw a few well made examples by an English bowyer. The bow seems like it will be really heavy, and come with an excessive amount of  hand shock by it's very design. Has any of you on this sight made ,and shot one? Just curious as to what results you may have had. Can't wait to finish mine, and get shooting it. Bob.