Primitive Archer
Main Discussion Area => Bows => Topic started by: nabiul on June 12, 2019, 10:42:08 am
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Hi everyone; long time shooter, first time bowyer here looking for some advice on bending some recurve+reflex into bamboo limbs. I've spent the last month learning the quirks of working with this amazing material and have had some failures so I thought I'd ask people with more experience before I ruin any more limbs. The problem I'm having is that while trying to bend a modest recurve the inside fibers of the bamboo always fail in tension. My first attempt was with a heat gun and I quickly learned that the material I'm working with is far too dry for this to work. My second attempt was with a 24 hour soak in water followed by steaming which worked for recurving the tip, but the shallower reflex didn't take on the rest of the limb; also once I removed the limb from the form a day later it began to straighten out. I figured that the straightening was from drying so I tried another steaming without a presoak this time and the inside fibers failed again. I'm thinking of trying a bending strap next, but will it actually do anything? As you know the grain is parallel in bamboo and it doesn't lift splinters like the strap is supposed to prevent. Do I need to make the limbs thinner for a successful bend? The form I'm using now has a pitifully small recurve/reflex and what I really want is something closer to the amount an asiatic bow has.
(https://i.imgur.com/YCNxxAQ.jpg)
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I'm not sure about bending boo that thick as I've never tried it, but thin bamboo bends like a dream. This was after maybe 2 minutes with the heat gun.
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Nabiul,this bow is made from bamboo slats that were belly heat treated.A lot of the back set does pull out,but if if you angle the limbs up from the riser ,and use longer ,sharper angled Siyahs you can come close to the profile you want.This one ended up with inch and half back set.It has a glued on handle, and wrapped. The siyahs are short to get the poundage I wanted because the slats were thin. It is 48 inches long ,and 45 lbs at 26 inches with cut in arrow shelf. Fun bow to shoot.
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More pictures
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Thanks for the replys guys. Nice bow Bassman, I'm considering doing glued on siyahs if all else fails but for now I really want to make a bow with smooth sweeping curves if possible. @ Bayou Ben, now that's what I wanted to see; I need to make the limbs thinner. But how stiff is that thin piece you've got? I don't suppose it would be strong enough for a 30# bow?
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If you want a smooth curve you can heat recurve in a thin piece of wood (maple works great) and glue that on the belly of your bamboo recurve (or flattened back if you use the bamboo in reverse). With the added glue line it will definitely hold the curve better.
If you want to make better use of the bamboo powerfibers you can glue 2 pieces of bamboo for back and belly with the pre-shaped wood recurve between it in the tips
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Nabiul, no that piece in my picture won't make a bow by itself. It was thinned for a backing.
I guess your options would be to make your bow like bassman's, or glue two bamboo slats together like leon mentioned.
I personally want to try a bamboo back/ wood core/bamboo belly bow with the boo on the belly charred to increase compression strength. I believe this is best utilizing the power fibers of bamboo and would allow for shaping as you like. But it is more complex than the options mentioned above. Check out James Parker's bows if you haven't already.
I received this bow as a swap and it is constructed like I mentioned: bamboo back/maple core/ charred bamboo belly. It's pretty fast.
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If you want a smooth curve you can heat recurve in a thin piece of wood (maple works great) and glue that on the belly of your bamboo recurve (or flattened back if you use the bamboo in reverse). With the added glue line it will definitely hold the curve better.
What do you mean it will hold the curve better, are you saying to steam bend the bamboo after gluing on a belly piece?
@Bayou Ben, laminations are too complicated for me right now. I'm new to woodworking as well as bowyering(?). I was originally planning to do a toasted belly but I tried some blue ink on the scrap pieces and it makes the tan belly look brilliant.
On another note, how do you guys get through that rock hard crust on the inside of the bamboo? It really makes using planes difficult and tends to tear out chunks of fiber.
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How long is the handle section supposed to be when shooting without a shelf?
(https://i.imgur.com/fKtlgdp.jpg)
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I make my handles 4" with 2" to 3" fades.
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My palm is about 4" wide so should I have a little extra room for the arrow?
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Limb #1 steamed in the oven in a foil packet covered by a wet cotton shirt after an 18 hour soak in the tub. Here's hoping it takes this time, going to leave it to dry on it's own for a while and then maybe hit it with the heat gun.
(https://i.imgur.com/eiQLWN6.jpg)
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My fears realized as soon as I applied the heat gun, instantly the inside fibers split. This flippin heat gun has caused way more problems than it has solved. I put in a couple of drops of superglue.
(https://i.imgur.com/oLNPvoX.jpg)
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if I'm bending a recurve ..I always boil... jm2c... gut
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Nabiul, no that piece in my picture won't make a bow by itself. It was thinned for a backing.
I guess your options would be to make your bow like bassman's, or glue two bamboo slats together like leon mentioned.
I personally want to try a bamboo back/ wood core/bamboo belly bow with the boo on the belly charred to increase compression strength. I believe this is best utilizing the power fibers of bamboo and would allow for shaping as you like. But it is more complex than the options mentioned above. Check out James Parker's bows if you haven't already.
I received this bow as a swap and it is constructed like I mentioned: bamboo back/maple core/ charred bamboo belly. It's pretty fast.
you are right Ben i shot a bamboo dragon from James for a couple years theyr quitr a bow .i know you could make one work too.
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I'm trying this with a scrap of bamboo to see what luck I have. Mine is about 3/8" thick and maybe 3/4" wide. I've got a caul that looks much like yours. I'll steam it and dry heat it to see if I have the same results.
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OK It went fine. It was a very dry piece of boo. I didn't soak it. I steamed it for 1/2 hour and clamped it to the caul. Let it cool/dry for a couple of hours and then heat treated it still on the caul to a light brown. Left it for another couple of hours and then did the other limb the same way but I heat treated to a dark brown. I didn't take a lot of care so the treating is a little uneven. It had 5 3/8" reflex when I f took it off the caul. Put it in the vice and grabbed a tip in each hand and pulled a half dozen times. The limb that didn't get as much heating straightened a bit. Lost about 1" of reflex total and I believe that most of that was in the middle where it was too thin and didn't get heat treated. It feels very springy. I may try this with a better piece of boo :D :D Did this sound like what you did?
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Yeah that's pretty much what I did, but the fibers pulled apart before I could get to even a light brown toast. Did you scrape away the hard crust on the inside of the bamboo like I did?
I wish it was that easy for me. Other than the bending and scraping away the hard crust on the inside, bamboo seems to be pretty much the ideal bow material.... for a beginner anyways.
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I sanded the inside with my belt sander until it was all a uniform thickness.
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How far away are you holding the heat gun? Is the boo still on the caul when you're heating it?
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I hold it maybe 3-4 inches away and move it back and forth, it was still cool enough for me to be able to touch it without any worry of burns when it cracked. It was on the caul, maybe my caul design is the problem; the limb comes under a great deal of tension once it cools from the steaming and springs back by a large amount once I loosen the rope.
Well other than being ugly, it should still work right since the belly is under compression only? I'm going to move ahead and see what happens.
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All I can think of is maybe try a different steaming method. The wet T-shirt in the oven doesn't sound like it's working. When you unwrap it is the shirt still wet and really hot? Maybe steam it longer. It has to reach boiling point for the full half hour or more.
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Yeah steam comes off the shirt for a while after you open it. I had no trouble bending it on the caul, it was really compliant, but like I said the reflex on the long part of the limb doesn't take which causes the recurve to come under great tension when it cools.
I will say that the appearance of the bamboo is different after my soak and steam, the fibers seem to have swelled and lifted up on the areas not covered by the smooth rind. On the next one I will try a long steam without a presoak.
Are you sure there are no tiny cracks in yours on the belly side?
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No cracks. How thick is your limb?
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A little over 2/8ths around the tip/crack area going down to much skinnier near the handle. Actually my raw material itself isn't that thick to begin with, I used the upper portion of the bamboo stalk which is thinner but has much longer spacing between nodes.
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Should I keep long fades or is it better to have more working limb? I originally planned for fades to end right at the nodes, but then I got worried about a hinge forming from steep fades or the handle and glue joint not being strong enough if I made the fades both short and shallow. I also want to avoid a situation where the forces in the power fibers make it to where the limbs end in the middle of the handle; I did a bending test on one of my previous failures against my shin and the rind and power fibers 'delaminated' from the softer bamboo.
I feel like I don't have enough working limb for a decent brace height and a long draw.
(https://i.imgur.com/f6rEPOL.jpg)
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Go to Dave Mead,s website.
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Actually I saw his videos on youtube originally and that's what got me to try making a bow out of bamboo, but I've done a few things differently which makes me uncertain on my design.
Well any ways it doesn't matter now. This was an absolute disaster, the handle is too round for my clamps to grip onto and I spent too long dicking around with the alignment while the TB3 was tacking. I'm going to wrap the fades with something when it's dry and CA the crap out of it.
(https://i.imgur.com/6tHHM6C.jpg)
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Is having a hinge bad even if I intend the bow to bend there? The right limb has a natural deflex right after the fade and then a hinge where the material is about 0.5mm thinner than the left limb. But as I understand it, this is the main working part of the limb anyways for a bow of this type right? I'm tempted to thin out the left limb in the same area to have it bend in the same profile because it looks appealing to me, bad idea? Also how do I approach the tillering process since bamboo is only so thick and already bendy to begin with, it's not like you can floor tiller it. It feels like I should have it braced already.
(https://i.imgur.com/RXQhzy1.jpg)
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Well I've wasted my life. I took it out to full draw and the bow has literally no weight, like 15# at 32". Is there a rule of thumb for shortening bows? It doesn't have to gain by much, I normally shoot a 30# olympic so a 30-35# trad bow would be ideal for me to start with.
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If anyone is still following, I'm going to try and save this malnourished bow.
A picture of the patient before the operation.
(https://i.imgur.com/IY6o3lC.jpg)
A little bit of the fade milled off to make a flat surface and the first incision. Diluted TB3 definitely does not soak through wrappings into the wood below.
(https://i.imgur.com/dEmXSxK.jpg)
Even more revelations about TB3, areas not exposed to air do not harden. The uneven joint at the end grain between the limbs was of a gel like consistency making a rubbery hinge at this point. Now I understand why Dave Mead is confident in using hot glue to assemble his bows, the gelled TB3 felt just like hot glue.
(https://i.imgur.com/VHb7cRJ.jpg)
And the first limb is off with most of the bamboo intact. My fears were unfounded, the poorly clamped TB3 joint was more than strong enough and stronger than either the bamboo or maple. More to follow in the future.
(https://i.imgur.com/AyRKHjC.jpg)
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What's your plan? I'm still watching :D
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Wrap the whole riser/handle area. Put glue down first for a little ways, wrap, glue another section, wrap and so on and finally add glue over the wrap, maybe watered down first then full strength. Trying to feather out your fades would help with the transition.
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Either use hot glue with a full wrap on the limbs to riser or epoxy.If you use hot glue you can correct your mistakes. You can heat it back up ,and the limbs will pull off the riser.If you use epoxy you have to get the line up right the first time. Mead sales quite a few of his bows, so he knows Hot glue, and wrapping work best, and is the cheapest way to go. TB3 is good stuff ,but not for this style of bow.
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The plan is to plane the limbs flat again, heat treat them and then glue them to some 1/4" thick oak slats. The oak would be worked to fade with the bamboo near the recurve and then assemble the whole thing again with the handle, maybe with a slightly more reflex this time. The question is whether to only heat the belly with a heat gun or do the whole limb evenly in the oven, and what would it do to the glued on tip overlays?
@Pat B, never thought about doing it gradually; initially I was just going to smear the whole area in glue and then wrap, but then I thought I would do a dry run first to see how it goes...and then I learned that I have two left hands and gave up the idea of wrapping on wet glue. Thanks, next time I will try it your way.
@bassman would you still say the same thing for gluing on oak overlays for 2/3rds of the limb length?
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Nabiul, here is a 53 inch knock to knock bow with tip over lays, FF string, and Oak riser.The limbs are made with Bamboo slats for the back, and heat treated Bamboo floor boards for belly that taper from end to end when tillered. The riser is hot glued ,and wrapped. The limbs are glued with Smooth On AD 40.Many guys on here use TB3 for limb glue ups with good success. I use Epoxy, because it is works best for me. This shows a different option. Maybe it will help. The working limbs are 20 inches long, and one and an eighth wide at the fades and taper to three eighth,s at tips. Over all length of the riser is 13 and three quarters of an inch. Braced at 4 inches it is 46 lbs. at 25 inches of draw.
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more pics
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Impressive, what do you think the max draw length is on that bow and have you ever chrony'd it?
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26 inches. Never chronied, but it is a snappy bow. Not trying to steal your thread Just thought I might be able to help you with some ideas.LOL.
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Is that artificial sinew wrapping at the tips? I wanted to use the stuff, but it's waxed and I thought it wouldn't adhere to glue. My preferred draw is also around 31" which I think makes bamboo only limbs impractical for me.
Update: I cleaned up and heat treated the limbs which went pretty terribly; all of the recurve straightened out once heated and the treatment is uneven. some lengthwise cracks also opened up which I filled with CA. I originally cut the limbs from two different slats of bamboo and didn't check the density, one of them is significantly more dense than the other. The less dense limb is now glued and clamped to the denser of the two oak slats I bought.
I think I'm going to do a oven heat treat for my next bow and do a dave mead style construction, any tips for temperature and length of time for a good heat treat?
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The first limb is dry and ready for cutting, second limb is glued up and under clamps.
(https://i.imgur.com/diJloDw.jpg)
The limb roughed out, you can see from the glue line that I didn't completely flatten the belly side before glue up because I was afraid of making it too thin. Again my fears were unfounded. It's stiff...really stiff.. like 100lbs to make it bend and it will explode in the process stiff. Next I'm going to try to thin and fade out the oak while judging how much meat to leave for my desired poundage.
(https://i.imgur.com/zNmyyw6.jpg)
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Back to tillering again, with more meat this time. right now it's sitting at about 40# near a short brace height. Not sure how I want this to bend now, the recurves are gone and it feels like the tips should be doing alot more of the bending this time. How should I do the belly; flat, trapped, curved?
(https://i.imgur.com/eydR03w.jpg)
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Flat is good. If anything maybe trap the back. Depending on the kind of Oak the bamboo might overpower it.
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Progress update.
I lost a lot of weight chasing out a hinge that formed in one of the limbs where the oak slat ended and transitioned to bamboo only. Now I'm scraping the other limb which is stiffer. Currently sitting at 35# at around 29" which is 2" shy of under my chin but it stacks rapidly if I try and draw it more. I'm afraid of going further and ending up with an underweight bow while trying to even tiller which may not even fit my shooting style which I don't even have yet.
(https://i.imgur.com/2f20IUC.jpg)
The tiller is obviously out by quite a bit but I thought I'd check exactly how much in photoshop by flipping and overlaying the image onto itself.
(https://i.imgur.com/Wqk2N18.jpg)
(https://i.imgur.com/Qc1Ap9T.jpg)
The awful string follow as was expected with bamboo after reading Tim Baker's article on bow woods.
(https://i.imgur.com/3krDeFW.jpg)
Now the million dollar question is should I take it to the field and shoot it or keep scraping the stiffer limb?
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this doesn't look too bad - just pretend the uneven limbs were done intentionally to get a positive tiller. i'd take it out and shoot it (-S if it's shooting good start a new bow. If it's not, start a new bow ;D cheers
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Strange thing about Bamboo. If you bend it with the outside as the back it will take set. If you bend it with the inside as the back it doesn't take set. I tried it with an offcut.
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The inside of the bamboo is soft like white woods while the outside is like true hardwood. All of the useful fibers are within like an 1/8th of an inch deep from the outside and they overpower the chalky soft inside fibers causing set.
The thing is the curved cross section makes for a really ugly bow with the inside of the bamboo as the back, unless you have really thick bamboo that can be worked flat without losing poundage.
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Would you rather have an ugly bow that shoots well or a pretty bow with a bunch of set?
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As the craftsman I'd take it as a challenge to find a way to have both. But set doesn't mean a bad shooting bow, all olympic recurves have a ton of deflex which is 'hidden' by the recurved tips and they shoot just fine. If you think about it, deflex and lower initial string tension should make for a smoother drawing bow so I don't totally see it as being a negative thing unless the set straightens out when the bow is left unstrung.
You also have the difficulty of attaching a handle and doing proper fades when using the bamboo in reverse; you'd probably have to make a handle that sticks out in front like on an assyrian style bow. Lots of things to try that could keep one busy for years to come.
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Well I took the bow out to the range and it shoots like crap; like a 20-25lb bow even though it was near 40lbs at my draw. The set just kept increasing as I was shooting until there was very little difference when it was unstrung, but it straightened out again when left that way. The cast is terrible, all of the work was being done after 28" when it stacks rapidly so small differences in draw on each shot caused wild variations in speed. The handle was awful too, the curve kept rocking in my palm leaving no consistency on placement between shots, which I thought might happen as the handle felt more comfortable to hold backwards while I was making it. I think the temperature difference between my cool basement and full summer weather also played a part in how wimpy it felt.
Lots of lessons learned and I've already started on my next bow; I'm going to try what I said in my last post with the bamboo bending in reverse with the handle glued onto the front of the bow. Basically the same as my first bow but held in reverse and no pyramid taper this time to try and get more poundage out of the bamboo.
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Ok so I've got bow#2 in glue up and have some reservations about bending the bamboo in reverse. The handle is on the front of the bow so when drawn there will be a huge peeling force along the glue joint and I don't think my hemp wraps are up to the task of stopping it from splitting the joint or the wood itself. Also Tim Baker's article mentions to tiller on the back when using bamboo in reverse, but how do you deal with cutting across the layers of fiber?
I think I have a good heat treat on the limbs this time; I did them in the oven and haven't glued on the siyahs yet so it's not too late to make it a conventional horse bow. What do you guys say, glue it up in reverse and try to make it work just for the sake of acquiring experience?
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Welp I guess I'm seeing this through to the end. I'll be sure to take pictures when the handle rips off and takes my fingers along with it.
(https://i.imgur.com/lFbiQbL.jpg)
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So far so good, pulling 28-29# at the position in the picture, the bamboo feels very light and 'weak'; it's not like wood at all. No signs so far of taking any set. I screwed up and misjudged the thickness of the left piece, a hinge has formed where I flattened it to glue on the handle; it bends right into the joint as I expected. I wonder if wrapping that part would help or would it just disintegrate over time from flexing?
(https://i.imgur.com/5nUg7VA.jpg)
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If you are at 30# where you are just don't do any more "wood" removal in the fades where it's thin. As you remove wood from further out it will take the strain off the thin part and it may(should) even out.
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I was doing that, but then I got greedy and tried to see if I could get more than 30# out of this bow. The back fibers let go right at the hinge at around 33-34lbs would be my guess. It's a shame because I think it could've made an efficient lightweight shooter if I tillered it to bend evenly all through, but I have no use for such a bow anymore; I need more weight. The good thing about this type of construction is that it's easy as piss to make a new limb, just a pain to disassemble and glue up again.
(https://i.imgur.com/hu9I6GR.jpg)
I removed the wrappings and cleaned up a bit of the glue, I was sure the joint would start peeling at least a little but no signs of it at all.
(https://i.imgur.com/05hjBnz.jpg)
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At what point do you stop reducing the thickness of limbs and start looking at reducing width? I'm back where I started; 30# at pictured which looks to me like a low brace. The new limb is on the left which is stiffer... and straighter than the right... which I still have to do more work on to get it bending evenly which means I have to take more material off the left limb to compensate. I also want the tips to be curving more to take stress off the new hinge which is right at the handle on the right limb.
I mean I get that the thinner the material gets, the closer the back and belly become to the neutral axis and the overall stress/strain on the wood reduces, but there must be a point where it's too thin for a safely functioning bow?
Yes I am tillering with a belt sander.
(https://i.imgur.com/K7L21Up.jpg)
(https://i.imgur.com/8vEYw0t.jpg)
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I know this is going to sound like a wise assed answer but I really think that when you start to wonder if it's getting too thin, that's the time too start narrowing it. I think you have to build a few bows with a particular wood to get a feel for the width/thickness thing. I believe that you get the best bow from the thickest wood you can that doesn't try to bend sideways. I also think that a thicker limb puts more stress on the back and belly so, again, it depends on the wood.
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I give up; the new limb exploded while I was trying to string it. It was stronger than the other limb but there was a node in the working section and the fibers split horizontally and lifted up right at the node while the power fibers on the belly peeled away. The entire limb also split lengthwise, I suspect the natural crown of the bamboo being on the belly caused this. I don't ever see this design working without a serious backing like sinew, but then how would you tiller it? Maybe a short draw long bow would work, but not the horsebow I'm trying to make.
I'm just going to have to live with the string follow from using bamboo conventionally.
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This is the latest iteration of the horse bow with the outside of the bamboo as the back, didn't even bother tillering much; it bent pretty evenly from glue up and was weak enough to brace and draw. I didn't think it was possible but it shoots worse than my first bow; initial string tension and stacking is not an issue, but it's so sluggish to cast and there is a ton of energy left in the limbs after the shot which goes right into your hand once the string hits the siyah. My plan was to use wide limbs to get poundage out of the bamboo, but I think now there's too much mass at the limb tips. Also lifted a 1/4 in section of the back near the handle I guess since no real tiller caused too much stress there, but that can be fixed.
Actually I'm liking my first bow now, it isn't a bad shooter at all if you pull a little bit into the stacking and use lighter arrows.
(https://i.imgur.com/DvYSqOE.jpg)
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This is the latest iteration of the horse bow with the outside of the bamboo as the back....
I would make the front profile look like a pyramid or even Eiffel tower. You might have to back the belly with bamboo or wood.
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This is the latest iteration of the horse bow with the outside of the bamboo as the back....
I would make the front profile look like a pyramid or even Eiffel tower. You might have to back the belly with bamboo or wood.
That's what I did with the first bow and if it comes to that I'll do it again, but for now I'm interested in seeing how the behaviour of the bow changes with less drastic changes like just tapering the tips into a pyramid or shaving the siyahs to reduce weight. What would happen if I cut new string grooves lower down on the siyahs? Would it bring up the draw weight? Then maybe I could shave the limb width.
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I read over this thread and couldn't find how long the bow is. What length are you looking for?
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It's about 5ft overall with the bendy parts of the limbs between 18-19" each. I don't care about the length, only the performance so I made it long enough to be what I thought was safe.