Primitive Archer
Main Discussion Area => Bows => Topic started by: simk on May 24, 2020, 02:30:04 am
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Hi All
For testing a new wood I quickly rushed an elbish bow - round belly. It's currently pulling 49# @ 28" and its 65" ntn.
Scale says it's 525 gramms, but according to Gardners mass theory it should rather be close to 400 gramms.
What's wrong? Overbuilt, too long? Should I pike it? How much?
As it's my first elbish bow, tiller critisism also welcome....I know, it's a little stiff towards right outer...and after handle area...?
Cheers
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Just my opinion.
It's fine :) maybe a hint stiff in the outer on the right limb (or is that the lower limb).
Some use the mass theory... some (like me) have never used it.
Like any tool, it has it's uses, but I'd never adjust the tiller of a bow I was happy with, because of its mass.... unless maybe I'd used the technique extensively and had 100% faith in it.
It's a mathematical model, a mix of theory and empirical to give a useful guide ... I wouldn't consider it gospel.
There is no disrespect for it at all, just my preference. A bit like a tillering gizmo, a great tool for helping newer bowyers get their eye in, probably a great time saver too especially on board bows, but not something I use and probably not relevant to all bows.
Del
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Thanks Del! Very helpful...
As a slave of the mass theory I just tought, the same bow piked and retillered to 49#@28", and - lets say 420 gramms - would throw an arrow farther and faster than it does now ;D wouldn't it? if not breaking ;D ;D ;D
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You"re testing a new wood (what wood is it by the way?)so no need to push it too far.
Was it taking much set? If it was I wouldn't pike it.
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it still keeps 1" reflex of 2" glued in. bellywood is fir (picea abies), sig of .7 🤣 pushing it to the limits 🤣
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My bows nearly always comes in a bit heavy. A lot depends on what you have in the handle and my wide pyramid bows never hit the mass theory. All though it is a very good tool during design and build.
Arvin
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I'm glad to hear that also your bows come in a bit heavy regarding Badgers theory, Arvin - can't be so bad then ;D
Sure with stiff handled bows there's always that uncertainty about the mass in the handle...but with the elb design, where every inch is working, it should be very exact. This bow just feels heavy in the hand...what made me start thinking and putting it on the scale. I'd be really interested on how heavy a well performing elb with 50# should be...?
As the wood does not show any signs of stress I'll probably pike it a little and work it down to 450gramms. Cheers
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At 65" ntn, I'd say its ok. taking an inch off each end wouldn't hurt too much tho' ???
To give some context... the flight bow I made last year 48# @27" boo backed Yew was 64" long and a whisker under 7/8" wide at the grip.
It weights 340grams, so maybe that does imply you are a tad overbuilt... remember mine is a boo backed flight bow and rather extreme, with limited stability and durability.
I'd suggest you shouldn't go below 64" as an ELB is working pretty hard at that length would arguably no longer be an ELB were it much shorter.
If you want to shed weight, maybe lose some width.
Personally I'd leave well alone.
Del
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Always on the hunt for the limit ...
I would do as Del suggested leave it alone, or maybe skinny the tips some more.
Interresting bow? - wood, whats the combo?
Good luck!!
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Del:
64" long and a whisker under 7/8" wide at the grip and 340grams
is impressive. how thick at the grip? mine is not finished. I'll do fps, then pike a little and reduce width and shoot it again. very curious. thanks for input!
b2w: with this one it's more about the legend of compression pine. its ash-backed. apart of the high mass I'm impressed so far (-S
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Nice bow. nothing wrong with that bend.
with this one it's more about the legend of compression pine. its ash-backed. apart of the high mass I'm impressed so far
Hi Simk,
tell us more about your compression "pine". I have used compression spruce, and it is an unusual wood. I once made a very similar maple backed larch bellied flatish elb that surprised me. the larch was from a board, and I have no idea if it was compression wood. (I have assumed it was not), while the spruce in a different bow was selected specifically for its compression wood content. Both woods acted in similar ways that is hard to describe. I think conifers exhibit some qualities that differ from hardwoods in compression. They seem to be able to recover from temporary set better. Could be that compression wood is a bit heavier than other woods for the draw weight, so I would expect the mass principle would need some correction for the materiel.
I would not cut the bow to pike it, but would try to clamp or lash down the string to a shorter draw to see where set starts to kick in harder. Resting the bow unstrung might show more recovery than you would normally expect from other woods.
Here is a pic of a Russian traditional bow that apparently can recover from an extended full draw. Please let me know if you do not want it in your thread.
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this really is a wicked constructrion willie (-S (-S (-S what the heck is that??? a prehistoric shooting machine ;D
there's lots of myths and rumours around this compression stuff, eg that its reflexing when getting more moisture. as spruce (thanks for clarification) is the most common tree here, there was a natural interest on my side.
bow is laid out with belly towards lower branchside. wood smells good from pitch. pitch pockets are a bad thing you can occur.
the storm had brought down a big tree 200meters above my home. couldnt resist to harvest a few very thick branches. cut some slats from the lower half.
I have tried thin ringed construction larch before. it chrysaled. they dont like compression wood in the construction wood because its warping all the time.. (-S i' impressed its really working on a round belly. and also how well its holding the profile. and I first time myself checked specific weight of a wood: .7 is far away from of normal spruce...definitly its different wood.
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what the heck is that??? a prehistoric shooting machine ;D
not sure how long ago it was invented, but it has been documented here.
https://vk.com/doc85016760_187383081 (https://vk.com/doc85016760_187383081)
Do you have any russian friends that can help with the translation? Google worked some, but I tried to parse the specific language describing the tree it came from with little luck. It appears (near the pics at the end of the article), that the spruce selected by the bowyer was a leaning tree, but not as extreme as some that I have found here. I have tried compressionwood that came from more extreme examples, but not like the pic in the pdf.
I see that you are using a branch. How long has the wood been drying?
I have tried thin ringed construction larch before. it chrysaled
I have found some very thin ringed larch, but the thin rings came from the outer rings of a very mature tree and had a high early wood ratio and was not very dense. I did find some better larch from another board. More than twice as stiff, actually.
http://www.primitivearcher.com/smf/index.php/topic,61908.msg868115.html#msg868115 (http://www.primitivearcher.com/smf/index.php/topic,61908.msg868115.html#msg868115)
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Mine has a little bit of Ash added on the belly at the grip for comfort.
At the grip it is 27mm deep x 22.7mm wide
Just beyond the built up belly it is 20.2mm deep x 22.3mm wide
mid limb 16.2 deep x 20.4 wide
Del
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Cool bow! Very interesting stuff.
Your bow could do with either more bend mid to outer right limb or less bend inner to mid depending on how you look at it :)
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Having no set in your bow will trump hitting a projected mass. I have made quite a few bows at the same dimensions and weight you built yours to and find at my projected mass the set is minimal but the wood you use will also affect this. Even thought I tend to treat all woods about the same as far as mass goes some woods should actually come in lighter, osage and yew can safely come in a bit lighter while some of the oaks should be mad a bit heavier as they are not as elastic.
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Thanks Willie for the interesting pics and read (????) 8) The unstrung profile of that "shooting machine" sure would be interesting. My wood was harvested on March 24 2020. I think it was dry. Still curious if it will change/warp somehow with further seasoning...
Thanks Del fur those numbers...sounds like formula 1 ;D
Thanks for judging that tiller bownarra! Finallizing it I'll take a few scrapes....
Thanks Steve Badger for clarifications - that really helps me to classify your mass theory a bit better - so it's not valid completly regardless of wood species...thanks.
After shooting the bow now it lost some more reflex (and a little puondage). It's almost straight now, which also is where I was aiming at. In my interpretation it's only some more stretch in the backing. At my 26" draw I got steady 172fps @ 10gpp and 177 @ 9gpp which I consider fine, considering there's still a little excess mass at the unshaped tips. The bow served it's purpose and showed that the wood is worth trying more complicated bows out of it. I will leave it as it is and not pike. have a nice day (-S
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That's pretty respectable speed from that bow.Nice bow too.
From what I've found is that some woods can handle different profiled bellys better than others with flat backs that are nonbacked.Osage is one that can.Yew too.
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thanks BowEd! I'm always using these ash-backings and got the impression that they are a bit stretchy and prone to take some set. In my wild imagination a boo backing would hold the profile much better and provide better performance? never used one...
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thanks BowEd! I'm always using these ash-backings and got the impression that they are a bit stretchy and prone to take some set.
The way to tell is to the saw the backing off. It's a bit drastic but very interesting. Saw it just under the backing. If the Ash is stretching it will show deflex once it's cut off. If a backed bow has some set and you saw the back off, normally the belly piece will show a lot of set and the back will be the same as when you first glued it up. At least on the two bows I did. I've never used Ash though, just Boo and Maple
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At my 26" draw I got steady 172fps @ 10gpp and 177 @ 9gpp which I consider fine
quite respectable speeds actually, considering the compression woods other qualities, I think the belly would have taken more strain in a more aggressive design, but it would not be as fast that way.
Please let us know if the bow recovers it's reflex.
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willie: it just lost glued in, artificial reflex so that will not happen I think. its still straight and didnt even start taking set. but for science I could string it for 3 days and then see if it relaxes to straight profile ;D It's not half as bad as DC's idea ;D but I still dont really like the idea a lot.
DC: What have you found out about the differences between maple and boo? Isnt the maple more stretchy. Does it preserve glued in reflex the same?
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I didn't really see any difference that I noticed. I trust the Boo more because you can tell which way the grain is going with Boo. With the kiln dried store bought maple that I had I was never sure that I had the grain just so. I just use the Boo now.
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Thanks DC. I dont have easy access to boo but one day will make a boo-copy one of my ash-backed ones to check that...With my d/r attempts I always loose 2/3 of reflex. Glueing in 2" of reflex on a flatbow and ending with little to zero? Is this normal?
willie: Its stringed. We'll look at it again tomorrow ;D it looks like some reflex has returned since shooting yesterday. but that again is probably the backing fooling around.
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Thanks DC. I dont have easy access to boo but one day will make a boo-copy one of my ash-backed ones to check that...With my d/r attempts I always loose 2/3 of reflex. Glueing in 2" of reflex on a flatbow and ending with little to zero? Is this normal?
I think there is too much going on to make a solid statement. You have set, pullout and at the same time sometimes you gain reflex in the first half of the tillering. Add all these together and you have confusion. At least I do. In the first half you have pullout combined with reflex gain countering each other so things go slowly. As you get further into it the reflex gain seems to leave so now you have set and pullout added together. Things happen fast. Confuses the he!! out of me ;D
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it just lost glued in, artificial reflex so that will not happen I think. its still straight and didnt even start taking set. but for science I could string it for 3 days and then see if it relaxes to straight profile
Simk,
just give it some time to recover, the wood is funny that way.
my maple backed bow lost its glued in reflex tillering and shooting in, but a few months* rest and it looks like I just took it out of the gluing fixture. Shooting it again makes it straight, but it eventually recovers.
**a few months for my bow because it is strained fairly hard I am thinking. I am going to try not working the wood so hard on my next one. This belly wood can be worked very hard. I have 42" birch backed compression wood with a cable back above the birch that I pulled to 75# at 20".
russian pics and buildalong here also.
http://www.primitivearcher.com/smf/index.php/topic,68162.0.html
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Do I remember reading something about these compression Pine bows being made and used wet. I don't know how they would accomplish that when all they had was hide glue. Don't know, maybe I'm misremembering ;D
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from what I have researched, they work in wetter envrionments. I cannot cite the report, but I recall one account of how the bows were lashed to trees outside in the winter to keep them from drying out too much and warping.
Did you try putting the branch bow your were having trouble with in a less dry place?
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Did you try putting the branch bow your were having trouble with in a less dry place?
No but summer is coming and the humidity will go up. I looked at it about two weeks ago and the string alignment was way out. I swore at it a put it in the COS. A few days later I took another look and the string alignment was good. Could be RH. Pretty much has to be actually, nothing else changes in the COS ;D ;D
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Willie, Awesome post about the Russian bowyer. Never heard of him before. Thank you.
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Pretty much has to be actually, nothing else changes in the COS
could be, but I have a different theory about your COS.
Bows get banished there for being uncooperative. They try to keep a low profile for fear of being tortured again.
When you went snooping around over there, like you did last week, and dragged a few out for another round of interrogation, it made the others straighten right up pretty.
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Does that make me a Bow Nazi?
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willie: it just lost glued in, artificial reflex so that will not happen I think. its still straight and didnt even start taking set.
Can someone explain to me the difference between 'taking set' and 'reflex pulling out'? To my engineer's mind they have to be the same thing. Either the glue line is moving or the wood is moving, it can't be anything else.
With the kiln dried store bought maple that I had I was never sure that I had the grain just so.
Isn't it just straight with no run off? If there is more black magic than just lining the grain up I am doomed.
Did you try putting the branch bow your were having trouble with in a less dry place?
(lol) (lol)
DC lives on Vancouver Island, there are no less dry places there, it is all wet.
Does that make me a Bow Nazi?
Maybe not a Nazi, but at least a hardass.
Mark
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With the kiln dried store bought maple that I had I was never sure that I had the grain just so.
Isn't it just straight with no run off? If there is more black magic than just lining the grain up I am doomed.
In one dimension I can see the rings. In another it's not so clear cut and I know it's close but, ehhhh!
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Can someone explain to me the difference between 'taking set' and 'reflex pulling out'? To my engineer's mind they have to be the same thing. Either the glue line is moving or the wood is moving, it can't be anything else.
To me "set" is damage to the wood so it's permanently changed from it's natural position.
When you have artificially, usually with heat, moved the wood from it's natural position to a new position and then, when you bend it, it goes back to it's natural position, that's "pulling out"
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The best way I have found to tell the difference is to see if the bow slowly returns to its position after unbracing. A bow that stays the same after unbracing will usually act more like a bow with no set. The more a bow returns the worse it is.
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To me "set" is damage to the wood so it's permanently changed from it's natural position.
When you have artificially, usually with heat, moved the wood from it's natural position to a new position and then, when you bend it, it goes back to it's natural position, that's "pulling out"
I agree set is compression damage to the cells. I see your point on the heat bending, but OP was talking about gluing in reflex and having it pull out. Since the original reflex strain was well below the threshold of damage to the wood (I assume it was well within the elastic limit of the material) and is glued into position instead of being heated, what is there to pull out? Something has to give for it to pull out, probably in the glue line or the wood right next to it.
The best way I have found to tell the difference is to see if the bow slowly returns to its position after unbracing. A bow that stays the same after unbracing will usually act more like a bow with no set. The more a bow returns the worse it is.
All right, that is a good working definition to go with.
Mark
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I agree set is compression damage to the cells. I see your point on the heat bending, but OP was talking about gluing in reflex and having it pull out. Since the original reflex strain was well below the threshold of damage to the wood (I assume it was well within the elastic limit of the material) and is glued into position instead of being heated, what is there to pull out? Something has to give for it to pull out, probably in the glue line or the wood right next to it.[\quote]
Yeah, that one doesn't work for me either. I'm not sure if I've noticed that. Glue ups are usually pretty solid.
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probably in the glue line or the wood right next to it.
An explanation similar to one of the theories behind perry reflex? I have always hoped to understand this better.
Consider the compression on the belly for a moment.
1. If one were to slice off a lam from the belly surface of an untillered bow, one could expect the lam to be just as stiff as any other lam sawn from the stave it came from.
2. if one were to slice off a lam from the belly surface of a bow that has been tillered and shot in, but shows no apparent set. one might expect the lam to be not as stiff as the lam above, but not necessarily deformed.
3. If one were to slice off a lam from the belly surface of a bow that has had the reflex "pulled out", I think one would find a lam that is permanently deformed and would take some effort to straighten. The rest of the bow might return to its glued in reflex profile.
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Evaluating set is extremely difficult, testing performance when finished is the only true test I think. A stiffer back can pull a rubberized belly back into its profile appearing to have no set when in reality the belly may have turned to jelly.
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after beeing on brace 23h I shot it a while and then tested speed - lost 5fps same arrows - did not count the best shot tough - drawweight @ 26" less 1,5# - set mainly on the outers - looks a little stressed - now curious how it behaves - put it outside over night - left outer is a natural deflex in the belly wood which was glued over an reappeared after bracing, not a good thing but no surprise.
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3369 were you testing a .270??
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Lol, That's one hell of a fast bow.
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and here's the result in pictures: before bracing, after bracing for 24h and then some full drawing...and a little while later. weather this is a good thing or not, this wood is somehow like rubber. its not something my ash backings usually do 8)
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I've never left a bow braced for 24hrs so I don't know but it looks pretty good to me. How does it look after a couple of hours of shooting?
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this wood is somehow like rubber. its not something my ash backings usually do
rubber is a good analogy. when I tillered a similar combo, I accidentally created a short section on each mid-limb that took a permanent set. otherwise, it seems to do like yours and eventually recover. I would have to bandsaw the bow apart to see if the areas of permanent set was created in the belly or the back.
seeing if the bow progressively slows (thru the chrono) as it is shot more would be interesting. and if you can set it aside and get the speed back next week.
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i will do that and shoot it some and report behaviour. i have a very similar ilex bellied bow to compare 😃
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I believe that contraption is a bow trap - an animal steps on the string set along the trail and it releases the arrow. The Kamba hunters/ poachers in Kenya decimated Tsavo National Park’s leopard population very effectively in the 1970’s using a fairly similar device and poisoned arrows. This was at the height of the leopard skin trade. Fortunately leopard are very resilient and their numbers bounced back quickly - but I believe the bow traps were a real hazard for anyone walking in the bush as the Akokanthera poison used has no known antidote. It’s interesting how similar effective designs pop up all over the world independently.