Primitive Archer
Main Discussion Area => Bows => Topic started by: AndyTurner on June 20, 2020, 06:38:57 am
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Hi, I'm fed up with trying to back bows with Bamboo. I want something more reliable that I can machine accurately.
I believe Hickory and Lemon wood work well but the shops are shut. I have one stave of IPE and a huge chunk of "Yellow heart" that I've never touched. I hear it makes good cores but I was wondering if it would make a good backing too.
My plan is
IPE Core - 58". Tip thickness = 3mm. Centre thickness = 6mm.
Yellow heart - 58". Tip thickness = 3mm. Centre thickness = 6mm.
Any experience / opinions welcome.
Thanks,
Andy
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If bamboo is not reliable and you can't "machine" it chances are it's not a material issue.
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Hi Pat,
On the one that fractured yesterday,
Bamboo - I sanded the entire length down to 3.8mm +/-0.05mm. Measured midpoint between the nodes, flat surface to crown apex.
IPE core - This I sanded down to 4.1mm +/-0.05mm
The first fracture occurred right next to a node. I sanded the area and offending node flat. The limb then fractured again further up the limb towards the handle. No where near a node.
Its like the Bamboo was too thin. On previous bows I had it thicker, around 6mm, but they warped on me & I read you need it thinner and no thicker than the core.
I find boo lustrating because of it's very organic shape.
I also find that it starts to split when you get up around 3mm. Last weekend I sanded about 6 lengths that all did the same. ....and I was being very gentle!
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Let's see some pics of the bows and the raw bamboo.
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If you are having trouble with Bamboo then it's for sure you will have major trouble with Yellowheart. It's pretty good in compression be weak in tension. If you are having trouble with the nodes then maybe you are too aggressive with them. I take the sharp ridge down at the nodes but besides that I leave them alone
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Yesterdays bow...
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Profile looks a bit too aggressive with that mid limb kinked reflex. Have you done a few straight glue-ups first or simple reflex?
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....errr no. As usual, I thought better to just jump straight in head first.
I've made a few Ratan bows for the kids but that's all. They work well.
The one's before seemed much sturdier but over powered. Some destructive testing in the vice showed the last one broke in the same place on both limbs. Unfortunately it had a twist in the middle so couldn't glue a handle on square. Looking back I should have strung it and put on the tiller board for better testing. Looks to me like
1. the glue is stringer than the wood.
2. On one limb the walnut sheered and the boo snapped clean.
3. On the other limb the boo sheered.
Frustrating but interesting.
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What kind of glue? How did you prepare the boo, belt sander? I've only made 15 boo backed bows but the backing has been bullet proof.
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hi,
1. I sanded the Back to final finish - 200 grit. This means at the end I'd have final thickness.
2. I sanded the Belly of the Boo square to crown
3. I used my "Boo sledge" (Plank of wood with high density foam) in the thickness planner
4. Plane down to about 5mm
5. Belt sand with 80 grit down close to 4mm
6. Switched belt to an old 80 grit and finished down to 3.8mm +/- 0.05. Measured mid point between noodles. Flat surface to apex of crown.
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oh...
EA-40.
Cured for 24 hours in w/shop. Then hotbox at 65 for 4 hours. Then left 24 hrs in hotbox for slow ramp down.
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mix was 50:50 by weight
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That all sounds god to me. I was told the other day that walnut is not very good for risers. Did you use walnut for the belly? In the pictures of the broken bow there is one that looks like the the grain runs from back to belly pretty quick. You may have had a "tectonic plate" failure.
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Yes. Used IPE / Walnut for belly. But...
1. Belly didn't fail on latest bow. It was the boo
2. On previous bow I deliberately broke the limbs to see how far they would go. Both flexed well before finally giving up.
In fact bow bows felt great. It was just that the last one failed because of the boo & I spent a lot of time on that one trying to get it spot on.
If i use another board for backing like Hickery or Lemonwood then its a lot simpler. Just chuck it through the bandsaw then the thickness planer with taper sledge.
Why is walnut bad for risers?
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https://www.primitivearcher.com/smf/index.php/topic,68249.15.html
Second page about halfway down.
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This is the pic I was referring to. See how the grain goes across the belly in about 4"? That's not good.
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Pau am is no good for backing as Marc said earlier. Reasonable in compression and good for pretty cores but not good for backing.
I hear what you are saying about the bamboo but it sounds like it is too high in moisture content eg. checking after being sanded. Warpage is another issue with too high an m.c.
Your profile is too aggressive (and not in a good way hahah!), as Pat mentioned the kink midlimb is no good. If you must go the r/d route to begin with (and I definitely wouldn't) then get the deflex off the riser then have a smooth curve from inner limb all the way to the tip. The curve should be flatter at the handle and can decrease in radius as you progress along the limb towards the tip.
I would definitely do some straight glue-ups first. The performance will be within a knat's crotchet of the r/d anyway. Your goal should be to learn how to tiller not some fancy profile. Leave them till later :)
Hickory will work if you can't be bothered to stick with the boo and just want to up the odds of success.
However do not disregard boo in the future it makes an awesome backing when done right.
No need to go finer than 60 grit when using EA40 or most other glues.
Good luck.
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I think you may be failing with the bamboo because of your lack of skill and knowledge with tillering high strain D/R bows. Thousands upon thousands of bamboo backed bows have been made.
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This is the pic I was referring to. See how the grain goes across the belly in about 4"? That's not good.
Hi DC, sorry chap I don't know what you mean. Can you mark up the picture please.
Thank you,
Andy
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If you look between the red lines you can see the split/break going from back(well, the back of the belly lam) to belly. Breaks follow the grain usually. That means the grain is running across the lam in about 4". The drawing shows sorta what I mean. this would be looking from the side. When the grain is like this and it bends it can push the grain apart and one side can slide under the other. Plate tectonics. The grain should go from one end to the other as much as possible.
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Ok, I may be wrong - its not unusual, but that just looks like straight grain that literally has been torn apart.
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Andy,
Have you checked the numbers on your design? you may well be overstrained at the failure locations.
Another possibility. Is all the boo that has failed been from the same lot?
The curve should be flatter at the handle and can decrease in radius as you progress along the limb towards the tip.
Mike, could you clarify please?
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Ok, I may be wrong - its not unusual, but that just looks like straight grain that literally has been torn apart.
Are you looking at the bamboo or the walnut/ipe(I'm not sure what that is)?
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Hi Willie & DC,
DC - I'm really sorry but I have no idea where this is going with the grain. I'm pretty sure the boo & walnut grain are running straight & true longitudinally. I still have the pieces. Tell me which bits you want to see and I will cut them up and photograph. Think Autopsy!!!
Willie - checked what numbers? i thought this whole thing was a suck it and see exercise. I'm just looking at stuff, guessing, testing and analysing the crash!!! Is there a model or some fundamental rule of thumb that I have missed?
Willie - yes, all the boo in the same shipment.
Right, I've been summoned to bed by she that must be obeyed. I'll check in tomorrow.
Thank you all for your input.
Good night,
Andy
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Can I see a nice clear closeup of the area I marked in red? From the same angle.
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Willie - checked what numbers? Is there a model or some fundamental rule of thumb that I have missed?
There are a few different modeling tools out there. Three that I know of written by forum members.
If you wish to input lengths, widths and thicknesses, then be able to view a graph of stress anywhere along the limb and at any stage of the draw. then I would recommend VirtualBow. It may be the simplest way to tweak your design if you have areas in the limb with excessive stress. There is a thread here you might ask questions in if you need assistance getting up and running.
http://www.primitivearcher.com/smf/index.php/topic,65115.30.html
BTW, the project has since been renamed, but I think you can still follow the link. Maybe lleroy can update the title of the thread and link, as he is the OP.
The other two are a bit more complex, and you will most likely need to provide more inputs to obtain usable results comparing your broken limb design to a remodel.
All three are capable of building a bow from "scratch" if you are willing to find the data for the inputs. I think mmattockx has a project going now using one of the other two that way.
i thought this whole thing was a suck it and see exercise. I'm just looking at stuff, guessing, testing and analysing the crash!!!
Plenty of folks prefer the old school way of learning, after all this is Primitive Archer :)
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Willie - so that the reflex will 'uncurl' properly.
Andy - as mentioned at least half of your problems are design related as I mentioned earlier. Just so you know I used to do this for a living and have made close to a hundred r/d bows - my and others advise is good :) - learn how to tiller on straight bows. R/d are hard enough to gewt right with a good starting profile.
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Willie - they are also much more stable made this way with less and more evenly distributed strain.
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Willie - they are also much more stable made this way with less and more evenly distributed strain.
Hi Bownarra - do you have a picture of a well tillered R/D bow at
1. Unbraced
2. Braced
3. Full draw
So R/D isn't just a "new trendy name" for "recurve"?
Thanks,
Andy
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DC - These are the pics you asked about.
I think the grain is straight. I broke this one deliberately just to see what would happen. Both limbs went in the same place - about 7" from fades towards tips.
Thanks chap,
Andy
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Just for everyones amusement - I was going thru my kindling supplies & reflecting...
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Number 1
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Number 2
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Number 3
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You didn't post a picture of what I wanted to see.
Can I see a nice clear closeup of the area I marked in red? From the same angle.
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Number 4
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You didn't post a picture of what I wanted to see.
Can I see a nice clear closeup of the area I marked in red? From the same angle.
Hi DC. Hows this?
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[
So R/D isn't just a "new trendy name" for "recurve"?
Thanks,
Andy
Definitely not although most recurves also incorporate D/R in their profile. In a recurve the tip also has the curve, not just the working limb.
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You didn't post a picture of what I wanted to see.
Can I see a nice clear closeup of the area I marked in red? From the same angle.
Hi DC. Hows this?
Can you see how the grain runs from one side of the walnut to the other in the width of the picture?
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[
So R/D isn't just a "new trendy name" for "recurve"?
Thanks,
Andy
Definitely not although most recurves also incorporate D/R in their profile. In a recurve the tip also has the curve, not just the working limb.
Pat I really don't understand. Please see attached. It's my bow and the bow I was trying to make. I really don't see any difference between a fibre glass recurve and what I was trying to create other than the materials and therefore limitations on geometry. For me the D/R is a recurve made of composite wood. It uses the same mechanics just different materials. Please do correct me if I'm wrong - I'm clearly new to this.
Thank you,
Andy
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You didn't post a picture of what I wanted to see.
Can I see a nice clear closeup of the area I marked in red? From the same angle.
Hi DC. Hows this?
Can you see how the grain runs from one side of the walnut to the other in the width of the picture?
Hey DC. Sorry no. Maybe its the angle of the shot. I have the piece right here. Please see attached. It looks straight to me.
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I really don't see any difference between a fibre glass recurve and what I was trying to create other than the materials and therefore limitations on geometry. For me the D/R is a recurve made of composite wood.
The 'D' is for deflex. Deflex is where the limbs sweep back from the handle area. The 'R' is for reflex. That is the limbs sweeping forward. The recurve is the tips being sharply bent forward. You can have any and all of these features by themselves or combined with the others. The fibreglass bow you are calling a 'recurve' bow is properly designated a deflex/reflex with recurved tips. The commercial designation of it as just a recurve is not really correct, but has become the default description of that type of bow.
Some pictures to illustrate.
1) A bow with only reflex. This was a flat pyramid bow that I heated reflex into on a form. There is no deflex off the handle and no recurved tips, the limbs simply bend forward from the fades:
(https://i.imgur.com/Zrjez0p.jpg)
2) A bow with reflex and recurved tips. No deflex off the handle, the limbs begin moving forward immediately after the fades:
(https://i.imgur.com/37f20Kw.jpg)
3) The same bow after tillering. You can see almost all of the reflex has pulled out so it is now essentially a flat bow with recurved tips:
(https://i.imgur.com/p1ZPTKj.jpg)
4) A bow with deflex out of the fades and reflexed limbs, but no recurved tips:
(https://i.imgur.com/ljF93Oh.jpg)
Mark
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You didn't post a picture of what I wanted to see.
Can I see a nice clear closeup of the area I marked in red? From the same angle.
Hi DC. Hows this?
Can you see how the grain runs from one side of the walnut to the other in the width of the picture?
Hey DC. Sorry no. Maybe its the angle of the shot. I have the piece right here. Please see attached. It looks straight to me.
Side to side it's perfect. I'm talking belly to back. The wood split at an angle belly to back.
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Andy, you are really struggeling hard. I also did (and do) with the r/d design. Only a few things out of my beginners point of view: A) Your design is from the fg-world somehow, not suited for wooden-world. B) The fades are a little steep and abrupt. C) The handle is too big and takes too much of working limb. keep struggeling. I have tried some different profiles and this one now works for me:
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I really don't see any difference between a fibre glass recurve and what I was trying to create other than the materials and therefore limitations on geometry. For me the D/R is a recurve made of composite wood.
The 'D' is for deflex. Deflex is where the limbs sweep back from the handle area. The 'R' is for reflex. That is the limbs sweeping forward. The recurve is the tips being sharply bent forward. You can have any and all of these features by themselves or combined with the others. The fibreglass bow you are calling a 'recurve' bow is properly designated a deflex/reflex with recurved tips. The commercial designation of it as just a recurve is not really correct, but has become the default description of that type of bow.
Some pictures to illustrate.
1) A bow with only reflex. This was a flat pyramid bow that I heated reflex into on a form. There is no deflex off the handle and no recurved tips, the limbs simply bend forward from the fades:
(https://i.imgur.com/Zrjez0p.jpg)
2) A bow with reflex and recurved tips. No deflex off the handle, the limbs begin moving forward immediately after the fades:
(https://i.imgur.com/37f20Kw.jpg)
3) The same bow after tillering. You can see almost all of the reflex has pulled out so it is now essentially a flat bow with recurved tips:
(https://i.imgur.com/p1ZPTKj.jpg)
4) A bow with deflex out of the fades and reflexed limbs, but no recurved tips:
(https://i.imgur.com/ljF93Oh.jpg)
Mark
Hi Mark - Nice write up. Thank you for that.
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PS. Liking the last one best! ;0)
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Andy, you are really struggeling hard. I also did (and do) with the r/d design. Only a few things out of my beginners point of view: A) Your design is from the fg-world somehow, not suited for wooden-world. B) The fades are a little steep and abrupt. C) The handle is too big and takes too much of working limb. keep struggeling. I have tried some different profiles and this one now works for me:
Hi SimK. Thanks for the pics.
No worries - I like a challenge. Just get frustrated sometimes.
Ok, so your profile is not dissimilar to mine - just slightly less radical that's all.
The most interesting thing I can see is that when braced and full draw - it looks just like a flat bow. A RC would still look like a RC.
Thank you for that.
Regards,
Andy
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Lets see what tomorrow brings
1. Top deck, a failed Ratan project about to become a deflex experiment.
2. Bottom deck. A previously rejected core about to become a flat bow project.
Good night all and thank you for your support,
Andy
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PS. Liking the last one best! ;0)
I wish that was mine, it is a beautiful piece of work.
Courtesy of silent sniper: https://www.primitivearcher.com/smf/index.php?topic=65941.0
Mark
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My plan is
IPE Core - 58". Tip thickness = 3mm. Centre thickness = 6mm.
Yellow heart - 58". Tip thickness = 3mm. Centre thickness = 6mm.
(http://www.primitivearcher.com/smf/index.php?action=dlattach;topic=68368.0;attach=154840)
A couple things not mentioned yet:
1) What is your draw length? 58" is very short for a wood bow, especially one with a stiff handle.
2) How long is the handle/riser on the bow pictured?
Aside from tillering an R/D bow as your first project, I think your main problem is not understanding how much weaker wood is than fibreglass and designing a wood bow based on a FG bow. At most, wood can stand about 1/4 the strain of fibreglass. That is for the best woods, the rest are less than that.
Your bow appears to be very short, with a long riser section. This is fine for a FG bow, but will not work in wood. Length is your friend with wood, both in terms of working limb length and using short riser/handle sections. The R/D bow from silent sniper that you liked was 63.25" NTN for a 28" draw with a short stiff handle section and that is considered short for that draw length.
The general rule of thumb for wood bows is minimum bow length = 2x draw length + 10". That gives a 66" bow for a 28" draw. Make your R/D bow 65-66" long and your chances of success will be much, much higher.
Mark
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Yes 58 is too short for even a glass bow. My shortest glass design is 58 and you have to do some funky stuff to make a 58 inch bow work for a 28 inch draw. Most definitely NOT beginner stuff! Refer back to my earlier posts if you want a working bow ;)
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My plan is
IPE Core - 58". Tip thickness = 3mm. Centre thickness = 6mm.
Yellow heart - 58". Tip thickness = 3mm. Centre thickness = 6mm.
(http://www.primitivearcher.com/smf/index.php?action=dlattach;topic=68368.0;attach=154840)
A couple things not mentioned yet:
1) What is your draw length? 58" is very short for a wood bow, especially one with a stiff handle.
2) How long is the handle/riser on the bow pictured?
Aside from tillering an R/D bow as your first project, I think your main problem is not understanding how much weaker wood is than fibreglass and designing a wood bow based on a FG bow. At most, wood can stand about 1/4 the strain of fibreglass. That is for the best woods, the rest are less than that.
Your bow appears to be very short, with a long riser section. This is fine for a FG bow, but will not work in wood. Length is your friend with wood, both in terms of working limb length and using short riser/handle sections. The R/D bow from silent sniper that you liked was 63.25" NTN for a 28" draw with a short stiff handle section and that is considered short for that draw length.
The general rule of thumb for wood bows is minimum bow length = 2x draw length + 10". That gives a 66" bow for a 28" draw. Make your R/D bow 65-66" long and your chances of success will be much, much higher.
Hello Mark. Thank you for the info.
The bow is for my daughter. She has a DL of 20.5”.
I just guessed at 12” for the riser. Her hand is 3” wide. 1” spare. 2” for fade = 6” x2 (for top of riser) = 12”. I also thought having a slightly longer riser would make it more stable for her.
I’m waiting for the glue to dry on the tips of a new “truly flat” bow. It’s incredible what happens when you glue the lams together - even with no deflection/reflex!!!!!
Thanks again for your time
Andy
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Wow. A bamboo backed Ipe bow for a girl? She must be very strong
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Wow. A bamboo backed Ipe bow for a girl? She must be very strong
...well she is my daughter - I’m pulling 70lb @ 28”. She’s got a hairy back too! 😂😂😂
She’s 8 years old. I measured her by trying her out on ratan bows I made for my girlfriends kids. They are a bit older. 10 & 12 yo. She’s pulling about 17lb @20.5”.
The new bow feels quite stiff. A bit too stiff. I figured I’d just tiller it down to desired draw weight.
It’s my son that worries me. He’s 6 and loves demonstrating that he can pull my girlfriends 25lb. Got to love the testosterone fuelled enthusiasm! 😂😂😂😂
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The bow is for my daughter. She has a DL of 20.5”.
I just guessed at 12” for the riser. Her hand is 3” wide. 1” spare. 2” for fade = 6” x2 (for top of riser) = 12”. I also thought having a slightly longer riser would make it more stable for her.
Ok, so you should be fine with a 58" bow drawing to 20.5". That mid-limb kink may still have been an issue for you. How far was the bow drawn when it failed?
As noted, 'boo and ipe seem like massive overkill for a 17# bow, you may have issues around getting the limbs thin enough and narrow enough to get down to that weight with materials that stiff.
Mark
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The bow is for my daughter. She has a DL of 20.5”.
I just guessed at 12” for the riser. Her hand is 3” wide. 1” spare. 2” for fade = 6” x2 (for top of riser) = 12”. I also thought having a slightly longer riser would make it more stable for her.
Ok, so you should be fine with a 58" bow drawing to 20.5". That mid-limb kink may still have been an issue for you. How far was the bow drawn when it failed?
As noted, 'boo and ipe seem like massive overkill for a 17# bow, you may have issues around getting the limbs thin enough and narrow enough to get down to that weight with materials that stiff.
Mark
Hi Marc,
I'm not really sure. I just put a string on and exercised it progressively until I heard it splinter. It felt like about 20".
I'm making the next one flat to simplify things and get something running. I'll make something curvy after I can make something flat.
This one is pulling 13lb at 17". See attached. (Yes I need to move the bow down the board - show's how much tillering I haven't done yet!!! ROLF :0))
Regards,
Andy
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I'm not really sure. I just put a string on and exercised it progressively until I heard it splinter. It felt like about 20".
Did you happen to measure the draw weight while you were doing that?
I'm making the next one flat to simplify things and get something running. I'll make something curvy after I can make something flat.
That is a good plan, even flat bows offer enough challenge to get them bending properly.
This one is pulling 13lb at 17". See attached.
The picture is pretty small to see much. What is the back profile? You look to have a reasonable elliptical tiller there but are showing circles for your reference. The bend should be matched to the back profile for the bow to work as well as possible.
Mark
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Another body on the slab. No.6.
Ok so yesterday I took the pic above. 13b @ 17". Everything looking positive. All I did was dye the back & sand the corners on the belly and back. I drew it back to 17", as per day before, and the boo let go.
Observations
1. The IPE held out. Its still in tact. I'd reuse it but the glue did such a good job some of the IPE is still stuck to the boo & visa versa.
2. The boo let go at one of the node points. I've sanded back the other node points and you can see where it broke would have been another node point.
Notes
1. I machined the boo flat to 4.5 mm
2. Using the taper sled, I tapered the boo tips to 3mm. The handle section was 4.5. It fades from tapered to constant thickness somewhere vague in the middle.
3. Prior to machining the boo I took some scrap boo, machined it flat, then tried to break it around the nodal areas. The boo refused to break at the nodal points. I tried around 10 node areas. The boo would fail outside the node area but close to it. This data caused me to think that machining the boo flat would provide a homogeneous material to play with. If it did let go then it would be between the nodes not at the nodes. Ero sanding the nodes would be cool.
Any thoughts?
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...here's a thought. Maybe I should back it with Unicorn tendons and saw his horn off to make tip & belly reinforcements? Just putting it out there! :0)
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I'm not really sure. I just put a string on and exercised it progressively until I heard it splinter. It felt like about 20".
Did you happen to measure the draw weight while you were doing that?
Andy - No sorry.
I'm making the next one flat to simplify things and get something running. I'll make something curvy after I can make something flat.
That is a good plan, even flat bows offer enough challenge to get them bending properly.
This one is pulling 13lb at 17". See attached.
The picture is pretty small to see much. What is the back profile? You look to have a reasonable elliptical tiller there but are showing circles for your reference. The bend should be matched to the back profile for the bow to work as well as possible.
Andy - Sorry - no idea what any of this means. The belly and back surfaces are flat. They are both tapered. 3mm tip. at the handle, 4.5mm on boo. 6mm on IPE.
Mark
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Another body on the slab. No.6.
Ok so yesterday I took the pic above. 13b @ 17". Everything looking positive. All I did was dye the back & sand the corners on the belly and back. I drew it back to 17", as per day before, and the boo let go.
Observations
1. The IPE held out. Its still in tact. I'd reuse it but the glue did such a good job some of the IPE is still stuck to the boo & visa versa.
2. The boo let go at one of the node points. I've sanded back the other node points and you can see where it broke would have been another node point.
Notes
1. I machined the boo flat to 4.5 mm
2. Using the taper sled, I tapered the boo tips to 3mm. The handle section was 4.5. It fades from tapered to constant thickness somewhere vague in the middle.
3. Prior to machining the boo I took some scrap boo, machined it flat, then tried to break it around the nodal areas. The boo refused to break at the nodal points. I tried around 10 node areas. The boo would fail outside the node area but close to it. This data caused me to think that machining the boo flat would provide a homogeneous material to play with. If it did let go then it would be between the nodes not at the nodes. Ero sanding the nodes would be cool.
Any thoughts?
Don't touch the back of the Bamboo. Not at all. Leave the nodes alone. Try that. If it still fails find another place to get the bamboo.
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I have built quite a few boo backed bows.. I dont sand my nodes either.. I leave them proud . I have a short 56" 55 at 28 boo osage .. reflex deflex screamer.. over 1000 arrows through her.. only boo bow I broke was ipe boo. r/d.. I was correcting tip alignment with heat ...strung.. hahahaha... I know... no need to comment..... she folded like a piece of paper...gut
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...the only other thing I can think of is acetone. I put the purple dye on too thick and used acetone to thin it. It's pretty toxic stuff. I also cleaned up some vinyl patches to fix the hot tub. They both curled up on application. Maybe the boo gets weakened by acetone?
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Andy - Sorry - no idea what any of this means. The belly and back surfaces are flat. They are both tapered. 3mm tip. at the handle, 4.5mm on boo. 6mm on IPE.
To clarify:
The back profile is the shape of the limbs you see if you look at the back or belly of the bow. It shows the limb width and how the limb tapers from side to side from the fades to the tips.
The tiller is the shape of the bend. Yours looks pretty elliptical, which is normal for a bow that has parallel sides on the limbs from the fades out to mid-limb and then a taper to the nocks from mid limb. The circles you show are the correct tiller shape for a pyramid bow where the limbs taper from the full width at the fades straight to the nock. You can tiller most any back profile to any bend shape, but there are optimal bends for different back profiles and it is best to match the two.
If I understand you correctly you machined/ground the outer surface of the bamboo flat? I think that destroys the high tension capacity that bamboo is used for and would likely be why your bamboo failed. Tapering also violates the grain on the face that is tapered. If you put the side out that has the grain violations on it that would also contribute to a tension failure.
Mark
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Are you grinding/planing the back of the Boo? If so that's your problem. I'd bet a dime on that. I usually only bet nickels ;)
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I went back and looked at your pictures. I don't see a node anywhere. There's no good pics of the back but any pics that show the back look like its been run through a planer.
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Hi Ok,
1. The latest No.6 is a pyramid bow.
2. I did machien the boo flat and then machined a taper.
3. On the previous curvy bow, No.5, constant thickness, I sanded the nodes but left the meat of the lumps in to preserve their strength. This however would have "cost strength" everywhere else. The boo curves across its width. This means its thinner (& therefore weaker) towards its edges. By machining in flat, then machining a taper, I thought I was creating a more "uniform, constant and homogeneous" layer of boo.
4. Fact remains that yesterday I drew it out to 17" and it was fine. All I did today was
1. Twist the string a bit to give a brace height of 5" instead of 3'
2. Apply dye
3. Apply acetone to thin dye
4. Sand the corners on back and belly
Pulling it back to 17" and having it pop on me implies something above caused a weakness and failure.
Regards,
Andy
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FYI. At the point of break, the boo is 4.5mm. The IPE is 4.7mm. IMO the boo should not have broken due to a "modest" bend.
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Andy,
You are a more patient guy than me. I would be taking a break (and a pint or three) between bow explosions.
Have you considered a different backing and maybe even a different belly wood to make a 20# bow?
It seems like at those thicknesses, the bow should be much stronger, and I suspect leaving the boo back natural, nodes and all, will bring different problems with the next one, but sanding them flat is just not a practical option.
In all honesty, a child doesn't need such a complex design. A simple 'D' selfbow will suffice. Kids out grow and accidentally break stuff.
you can learn a lot about bow building with any size bow, but your materiel's are suited for stronger bows.
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FYI. At the point of break, the boo is 4.5mm. The IPE is 4.7mm. IMO the boo should not have broken due to a "modest" bend.
The Bamboo looks quite flat which leads me to believe that you are planing or flatting the outside of the Slat before gluing it up. Mark and DC asked you that specifically but you've ignored them both which makes me wonder exactly what is going on here.
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FYI. At the point of break, the boo is 4.5mm. The IPE is 4.7mm. IMO the boo should not have broken due to a "modest" bend.
The Bamboo looks quite flat which leads me to believe that you are planing or flatting the outside of the Slat before gluing it up. Mark and DC asked you that specifically but you've ignored them both which makes me wonder exactly what is going on here.
Hi Marc, I'm sorry but I didn't ignore Marc or DC. I stated,
"2. I did machien the boo flat and then machined a taper."
and
" 1. I machined the boo flat to 4.5 mm
2. Using the taper sled, I tapered the boo tips to 3mm. The handle section was 4.5. It fades from tapered to constant thickness somewhere vague in the middle.
3. Prior to machining the boo I took some scrap boo, machined it flat, then tried to break it around the nodal areas. The boo refused to break at the nodal points. I tried around 10 node areas. The boo would fail outside the node area but close to it. This data caused me to think that machining the boo flat would provide a homogeneous material to play with. If it did let go then it would be between the nodes not at the nodes. Ero sanding the nodes would be cool."
What's going on is, I'm learning from others who are more experienced and knowledgable than me, but at the same time as experimenting proving things to myself in order to gain a thorough understanding and confidence in what I'm doing.
Thank you and kind regards,
Andy
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Andy,
You are a more patient guy than me. I would be taking a break (and a pint or three) between bow explosions.
Have you considered a different backing and maybe even a different belly wood to make a 20# bow?
It seems like at those thicknesses, the bow should be much stronger, and I suspect leaving the boo back natural, nodes and all, will bring different problems with the next one, but sanding them flat is just not a practical option.
In all honesty, a child doesn't need such a complex design. A simple 'D' selfbow will suffice. Kids out grow and accidentally break stuff.
you can learn a lot about bow building with any size bow, but your materiel's are suited for stronger bows.
Hi Willie, red wine is my soul mate!!!
True I could just make another ratan D-section but I really want to solve this.
I'm only going to change one variable at a time. The next obvious choice is the backing material. For me personally boo is not practical. I'm sure its great when you get the hang of it, or maybe I just got a bad batch as someone suggested. I need something I can machine quickly & easily - I have X5 very keen little customers. I'm thinking Lemonwood now! :0)
In terms of the core wood. IPE is very popular. If you look at the performance numbers on the wood database then I can see why. On paper it performs better than Osage and Lemon wood. I can't find anything better. I don't understand why it's good for strong bows and not light bows too. I've managed to thin it down to ball park performance requirements and on the bows that have shot it felt great. Why would you use a lower performance wood?
Regards,
Andy
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I don't understand why it's good for strong bows and not light bows too.
equally suited for all, if the bows are kept proportional. just not necessary for such a light bow I guess. Now if you want to make the fastest kids bow at the clubhouse, then you have the right stuff.
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I don't understand why it's good for strong bows and not light bows too.
equally suited for all, if the bows are kept proportional. just not necessary for such a light bow I guess. Now if you want to make the fastest kids bow at the clubhouse, then you have the right stuff.
Well just £300 on 3 bits of wood.
..more IPE, Lemonwood & Hickory. Something should work! (lol) (lol) (lol)
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Andy... get Dean Torges bamboo bow video... appears to me you are flattening the boo at the nodes and that is why your bows keep breaking... watch the video take notes .. will save a lot of time and work... I lightly hit nodes but leave them proud and scrap rine off with scraper.... video will show all.... gut
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Hi Marc, I'm sorry but I didn't ignore Marc or DC. I stated,
"2. I did machien the boo flat and then machined a taper."
and
" 1. I machined the boo flat to 4.5 mm
2. Using the taper sled, I tapered the boo tips to 3mm. The handle section was 4.5. It fades from tapered to constant thickness somewhere vague in the middle.
3. Prior to machining the boo I took some scrap boo, machined it flat, then tried to break it around the nodal areas. The boo refused to break at the nodal points. I tried around 10 node areas. The boo would fail outside the node area but close to it. This data caused me to think that machining the boo flat would provide a homogeneous material to play with. If it did let go then it would be between the nodes not at the nodes. Ero sanding the nodes would be cool."
What's going on is, I'm learning from others who are more experienced and knowledgable than me, but at the same time as experimenting proving things to myself in order to gain a thorough understanding and confidence in what I'm doing.
Thank you and kind regards,
Andy
Well that's your whole problem then. Leave the back of the boo alone and it will stop breaking on you. Don't even touch the nodes
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I agree with Marc as stated earlier... when you flatten the boo you are destroying its power fibers basically violating it... and BOOM... there is the problem.. flatten boo on belly ONLY... taper your belly wood... if inducing reflex deflex in glue up... get the video and watch it.. gut
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I'm only going to change one variable at a time. The next obvious choice is the backing material. For me personally boo is not practical. I'm sure its great when you get the hang of it, or maybe I just got a bad batch as someone suggested.
Bamboo is a superb backing wood, you have destroyed its properties by machining the outer surface flat. Leave the outer surface and nodes intact and you will never break a piece again.
In terms of the core wood. IPE is very popular. If you look at the performance numbers on the wood database then I can see why. On paper it performs better than Osage and Lemon wood. I can't find anything better.
You are getting your terms mixed up. Ipe is a superb belly wood. The core is the bit in the middle between the belly and the back and it doesn't do much in terms of carrying the load.
I don't understand why it's good for strong bows and not light bows too. I've managed to thin it down to ball park performance requirements and on the bows that have shot it felt great. Why would you use a lower performance wood?
It's not that ipe is bad for light bows, but it is unnecessary and you can use a cheaper wood that is easier to work and get the same results on a kids bow. The other issue with it is that you end up super thin on the limbs and it is hard to tiller them when they get that thin as even a small scraping ends up having major effects.
..more IPE, Lemonwood & Hickory. Something should work! (lol) (lol) (lol)
If you have decent, straight grained hickory available to you it will work much better for what you are trying to do, just make sure to put the tapered face in towards to the belly wood and keep the back face intact.
Mark
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Marc, Gut & Marc. Thank you chaps. Have a great weekend, Andy.
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If you have decent, straight grained hickory available to you it will work much better for what you are trying to do, just make sure to put the tapered face in towards to the belly wood and keep the back face intact.
Mark
Just one last thing Mark - it doesn't seem intuitive to me to glue tapered surfaces together to preserve the back face. The back would have been machined anyway.
For me it makes more sense to glue the flat surfaces together as per attached.
Please can you explain.
Thanks in advance,
Andy
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Just one last thing Mark - it doesn't seem intuitive to me to glue tapered surfaces together to preserve the back face. The back would have been machined anyway.
For me it makes more sense to glue the flat surfaces together as per attached.
Please can you explain.
You bet. If the grain runs parallel to the flat face (a big if in a lot of cases) then the tapered face is cutting across the wood fibers at an angle, exposing the end grain similar to other grain violations. If you put this face on the back of the bow where it sees maximum tension then those exposed end grain locations are more likely to lift a splinter than the flat side with the theoretically continuous fibers running end to end of the lam. This only matters on the back lam, the belly is far less sensitive to exposed end grain and other grain violations.
I don't know that this is much of an issue when you are taper grinding lams as you are, as the taper is very gradual, but stresses are high enough in a bow that I always do everything I can to tilt the table in my favour and doing it this way costs nothing extra but may help deliver a functional bow in the end.
Mark
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The back would have been machined anyway.
I'm not following you. Why would the back have to be machined?
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I don't know that this is much of an issue when you are taper grinding lams as you are, as the taper is very gradual, but stresses are high enough in a bow that I always do everything I can to tilt the table in my favour and doing it this way costs nothing extra but may help deliver a functional bow in the end.
In fact, if you are getting the backing lam out of a thicker board, you would actually want to prep the back facing surface of the lam to best follow a ring (or the grain if not flat sawn.)
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You bet. If the grain runs parallel to the flat face (a big if in a lot of cases) then the tapered face is cutting across the wood fibers at an angle, exposing the end grain similar to other grain violations. If you put this face on the back of the bow where it sees maximum tension then those exposed end grain locations are more likely to lift a splinter than the flat side with the theoretically continuous fibers running end to end of the lam.
Hi Marc. I see clearly now! Guess who put his tapered surface on the back facing the target?! :OK (LOL)
I'm not following you. Why would the back have to be machined?
Hi DC. Because when I make lams I flip the boards during the thickness process to make sure everything is flat and square before I taper it.
In fact, if you are getting the backing lam out of a thicker board, you would actually want to prep the back facing surface of the lam to best follow a ring (or the grain if not flat sawn.)
Hi Willie. Noted - thanks. I didn't think of that!
I was on the phone to the nice man selling me the wood. He assured me that you can't back a bow with Lemonwood and that I needed Hickory. I read somewhere on the web that you can use Lemonwood on its own because the grain is always straight and tight. I bought both in the end just to play with & see for myself.
On the wood database (https://www.wood-database.com/lemonwood/) the Modulus Of Rupture, which I'm using to estimate tensile strength, is 22,100 lbf/in2 (152.4 MPa). Hickory on the other hand is ballpark less, e.g. Water Hickory is 17,800 lbf/in2 (122.8 MPa), Shagbark is 20,200 lbf/in2 (139.3 MPa). Bamboo is between 11,020 lbf/in2 (76.0 MPa) and 24,450 lbf/in2 (168.6 MPa). It doesn't mention species. IPE for reference is 25,660 lbf/in2 (177.0 MPa).
I'm guessing MOR alone is not the deciding factor in choosing a wood for backing. Looking the very popular boo - I'm guessing the rind itself must naturally seal in the grain preventing the splinters from lifting. That said most people scrape that stuff off. Looks to me now like its the best and cleverist bit for backing material.
Do you have any favourite reading on making wood backings?
While you're there, do you have any favourite reading on making wood laminated bows?
Thanks,
Andy
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I wish I knew of an authoritative reference for lam bows to recommend, and there may well be one out there, but I am not aware of it.
searching this site with google works better than the forum search. for example...
hickory backed site:http://www.primitivearcher.com/smf/
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Hi Andy... this thread has kept me on the edge of my seat ... but I can’t decide if in part it’s like watching NASCAR for the crashes! Keep going you are nearly there and clearly persistent ... but some thoughts that might really help...
Have you read any of the Traditional Bowyers Bibles? Vol 1 and Vol 4 have some very useful chapters that I think would solve many of your issues. Along with the Dean Torges video on bamboo backed bows as suggested earlier. Or some of the great you tube videos on making a board bow?
There is some world class advise you are being given by some truly gifted bow makers on this forum, but sometimes it pays to take the time to learn the terms and basics...
I would really focus on making a few straight board bows - especially if they are just for kids.
I don’t know where you are based - and I know it’s hard with the dreaded virus - but if you can find a timber yard and pick through the lumber - oak, hickory, ash - and pick your own wood with the correct grain orientation and start tillering and making bows, you will learn a lot about wood and the process of tillering.
Once you have a few tillered working board bows, you can always glue a bamboo backing onto them and start playing around again. I am not sure that this “destructive testing” is that helpful - better to learn to make them so they stay together and then start pushing those limits...
Do you have a band saw and a belt sander? You can thin a bamboo back with these two tools in about 10 minutes. Even a hand held belt sander you can clamp upside down in a vice. You really don’t need to be worrying about thickness tapers and stuff like that right now.
Draw the profile of your bow on the bamboo and cut it out. Then turn it sideways and cut it to within a few mm of the back. Put some 40 grit sandpaper in your belt sander and get a piece of wood to hold the bamboo down against the belt which helps avoid pruning your finger tips. Pull the bamboo strip towards you against the rotation of the belt whilst pushing down with the wood. Sand the bamboo until the edges are nearly sharp. Use the wood to put extra pressure where you need more bamboo removed. Sanding till the edges are sharp once the back profile is cut out will naturally taper the bamboo towards the tips anyways.
DO NOT touch the shiny back of the bamboo ... and if you do it should be with sandpaper right at the end and only enough to take the waxy rind off if you plan to stain/ finish the bow.
If you glue this onto an already tillered board bow you will up the poundage, and you can even start playing with shapes at that stage like gluing in R/D and you will understand what is happening along the way.
A bamboo backing is an amazingly simple and easy thing to do if you don’t overcomplicate it!! You are doing something very wrong to break this many bamboo backs. Even poor quality bamboo is very strong in tension.
If you do like grinding lams and tapers and gluing things up in a way that is pre-tillered, you may do well to visit Binghams store online and buy a kit for one of those bows we aren’t allowed to mention here! The kits come with instructions for the bowyou choose, the correct tapers and parallels for the poundage you want and if you follow the instructions step by step you get a pretty decent bow! Albeit the kind we cannot mention here...
But the process will teach you very little about how to tiller a wood bow - which is an art in its own right...
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I generally don't read through all these long threads but did this one, all I can say is Andy, you have the patients of Job, good luck. :)
Pappy
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Hi,
this forum could use a "like button" function. So many of you have been so kind and useful. Thank you.
Ok, so while waiting for my new wood to rock up I built another IPE/Bamboo bow. I reused the handle, a disgarded Belly&Core (its just one bit of wood, the profile wasn't perfect for an end bow), and tapered up a new Bamboo back. I baptised it "Franken Bow". I had it on the tiller board and for one brief glorious moment in time it was all symmetrical, pretty & beautiful. It truly was awesome!!! The only problem was it was pulling like 20b at 8". I'm not sure who said it but I concur. You were right - I was wrong. Its a learning experience. IPE is no good for light bows. I sanded & sanded. In the end the IPE was ridiculously thin, like 1-2mm, and in a couple of spots I ground down to the boo. Please see attached.
On a more cheerful note, the Lemon wood and Hickory rocked up. Let me tell you...
1. Lemonwood is "absolutely gorgeous" to work with. Really, truly, its like a seductive butter by comparison. you just want to stroke and admire it. It's beautiful. That said it gives ZERO warning when it "lets go". By comparison, Ratan will send you a courtesy email 2 weeks in advance, then reminders. In the end it just gives in with no drama or danger to the user. Fab for kids bows. Unbacked IPE - the limb, thankfully, shot past my eye and entered a new timezone before I realised what had happened. I never did find the broken limb. Testing scraps of Lemon wood verses IPE, well less just say that Lemonwood will give about 1/10ths notice compared to IPE Great. At least you can hear the IPE splinter first then boom. The Lemon wood is just like "Boom baby"!!! That said it's so seductive & bends so nicely compared to IPE! :0)
2. The Hickory looks to be your flexible friend and I can see why people recommend it for a backing. Please see attached!
I'm really looking forward to seeing what happens! :0)
Thanks again for all your help & patience,
Andy