Primitive Archer
Main Discussion Area => Bows => Topic started by: bubbles on April 25, 2013, 06:14:23 pm
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Hi there, had my first violent bow explosion today. Trying to make a bow for my buddy with a long draw - 30 inches, and had the bow explode at 29.5. It was 68" ntn, 2" wide from the fades to 1" past mid limb were it tapered to 1/2" at the nock area. I had it braced at 5 1/2" and it had about 2" of string follow when it blew. I heat treated it (first) and backed after I had it bending 20"@ 1" brace, waited a week for re-hydration. Maple board backed with linen canvas, the grain wasn't perfect, but it was pretty good, in fact the break happened where the grain was straightest. The stiff handle including fades was 10" long. I realized after I had roughed it out that I should have probably made it 2-4 inches longer for such a long draw.
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Looks like both limbs right out of the fades could have been bending more. A liitle extra length would have helped. Sorry about your bow, now you get to have more fun trying again.
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I mostly dissagree with Red Tailed Hawk, but I can see a tad more bend right out from the fade would help ... BUT
IMO the outer half of each limb isn't doing much work which is overstressing the inner 1/2 - 1/3
Did the limb have any thickness taper?
It's what I call a slightly 'square' tiller e.g As a vastly exagerated explanation of what I mean. Flat in the middle third, then a right angle bend and the last third of each limb coming straight back.
Obviously it's not that square, but if you hold CD or something circular up the the picture you can see the tips are not working as hard.
Del
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This pic illustrates what I mean...
Even if we allow for the stiff handle (2nd pic) and just look at the curve of the upper limb and fit an ellips it shows a bit too much bend near the centre and not much in the outer third.
... let's hear from everyone else.
Del
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Ahh, I should start drawing ellipses on my tillering pics from now on.
There was thickness taper about to the point that the width taper started taking over, but it may have been too slight. The poundage was #45, I forgot to mention that. I think I left the outer part of the limbs a little stiff as I didn't want the bow to stack when I got way out to 30", maybe I left them too stiff.
I was also going by the "tiller should agree with limb shape" in that I should have been putting most of my bend in the wider sections of limb that can handle it more.
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I think del nailed it, for a 30" draw go with an elb style, that's what i'd do, or a bendy eastern woodland, I just finished one from a hard maple BOARD and it would easy make 30", 59 1/4" ntn
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I think everyone has a point here. You could have made it longer, I would not have. It could start working closer in to the fades AND the outer 1/3. Most of your bend is in the middle with little happening elsewhere. All of these would have relieved the stress midlimb where it broke.
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I wouldn't have made it any longer, but i'd go elb style for that draw, bub
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I think I have to echo what Del said, something more needed to be bending. If your fades are 2" and mid limb has already tapered to 1", that's pretty drastic, even for a mollegabet design. I bet it would have blistered an arrow.
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hmm the pic looking at the inside of the break looks similar to my hickory bow that broke at a chrysal. but what do i know. good luck on your next bow. SS
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I think everyone has a point here. You could have made it longer, I would not have. It could start working closer in to the fades AND the outer 1/3. Most of your bend is in the middle with little happening elsewhere. All of these would have relieved the stress midlimb where it broke.
+1
Jon
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I think I have to echo what Del said, something more needed to be bending. If your fades are 2" and mid limb has already tapered to 1", that's pretty drastic,
Sorry, let me clarify, It was 2" wide from fades to past midlimb (sides parallel). The width taper began 1" past midlimb, the to 1/2" at the tips.
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i knew what you were saying bubbles, its a nice attempt. so tell me, what was the weight on this bad boy before it blew? i would always use a scale, granted the limbs were over-stressed, but the limbs could be pulling more than you wanted in the first place, so the may have exploded partly because of that! weighing helps you to avoid over-stressing past target weight. but of course if the bow was bending too much mid limb and not enough fades and tips it could have blown anyway. several factors can be critical in determining weather or not your bow will turn out or not.
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that's all good muffin, don't know if he has a scale but sometimes ya just gotta make do with what ya got, not saying your wrong, heck all I still have for a scraper is a 6" lockback knife
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Are we talking a scale to measure poundage of the bow? I used to use one and I didn't like it. I just have a bag filled with weights that i fill to the desired poundage, with three caribiners that simulate fingers. I pull the bow with a tape measure hanging from the handle to get the draw at that poundage. Then I have an arrow with and elastic band that is my draw check and I shoot a video of me drawing the bow to that length. This one was 45# @ 29.5 when it blew. Never drew it past 45#
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I also agree with Del that outer limb is not doing much work. A bendy handle design would help you get to 30" draw at a shorter length.
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I'd say the problem is you made it from a board and board bows are unpredictable
How are boards unpredictable?? The grain tells you EVERYTHING you need to know!! Learning how to read what it's telling you is the hard bit. ;)
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Personally I tend to stay away from quarter sawn boards. The grain must be straight-edge straight when you use quarter sawn. At a glance it may look good to go but a lot of quarter sawn wood will break your heart!
Also linen doesn't do a whole lot of protection. Thick rawhide is tougher.
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To me, the virtually straight across break to me looks like dry rot, or the wood being too dry. Maybe length wouldn't have mattered in this case. However, I would agree with your first instincts that it coulda been a couple of inches longer. Draw length at 30, times 2 equals 60 + 10 inch stiff handle totals 70". Basic rule of thumb. Being backed, you might have gotten away with the couple less inches. Osage selfbow might be able to take it but I'm not so sure about the maple board. Just my two cents...
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I have gotten away with some shocking tillers early on and never had a break like that. But... I have only ever used staves and not boards. Not saying boards are any worse or better but I know where my staves have come from, how long they have dried and if they have ever been badly treated or not.
Commiserations.
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What Matt said,glad he typed it so I didn't have to. :) :) A little more bend in the fad and little less at mid limb, Might have helped,I usuall keep the outer 1/3 fairly stiff on mine also. :)
Pappy
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Fades too stiff, don't have a problem with the tips. Sorry it broke, I know you worked hard.
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Hi bubbles,
If you don't mind can you tell me what the moisture content of the bourd is?
4giveme
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Out of interest, if you put something with a right angle like a business card or corner of a sheet of paper up against the pic. You'll see the string angle is still well short of 90 degrees and therefore nowhere near giving the effect of 'stacking'.
Say it's 5 degrees less than 90, we all think that's fine... If it was 5 dgrees over the 90 would everyone be wailing in horror? I dunno, just askin'
Del
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A 68" bow with a 10" handle, drawn 29.5" means you drew it way too far. When the working limb is 2x the draw it's a bad situation. Quarter sawn needs perfect edge grain tip to tip straight as Mike said. May I suggest a board bow with a working handle-1.5" for 50 # and 1 3/8" for 45#. 69-70" for at least for the draw mentioned. See my site. Jawge
http://georgeandjoni.home.comcast.net/~georgeandjoni/index.html
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Aside from all the other good suggestions ... Limbs could have been a little wider thinner, instead of a longer bow .... but like MW said , it just looks like a bad piece of wood ... Happens !!! :(
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Hi bubbles,
If you don't mind can you tell me what the moisture content of the bourd is?
4giveme
I don't have a moisture meter, so I dont know. That could have been part of the problem.
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I'd say the problem is you made it from a board and board bows are unpredictable
Rubbish.
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I agree with the bend issues, but is that rock/sugar maple? There are other maples that look similar, but are a lighter wood. :)
VMB
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More rubbish.
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More rubbish.
I agree 100%
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What's rubbish?
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Looks like somebody deleted a couple of posts! joe123cable?
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grarbage, trash, the statement that this bow broke because it was a board, all rubbish
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Looks like somebody deleted a couple of posts! joe123cable?
the magical disappearing statement :laugh:
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Yep, that is rubbish. Wood is wood, it can be too dry, too wet...but it is still wood. ;)
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Looks like somebody deleted a couple of posts! joe123cable?
the magical disappearing statement :laugh:
Yup... guess he changed his mind.
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Looks like somebody deleted a couple of posts! joe123cable?
the magical disappearing statement :laugh:
Yup... guess he changed his mind.
Haha nope didn't change my mind just don't wanna argue with people
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Good idea!
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Yeah, my post got deleted also! But I had it copied ;D! Here you go..................
Not knowing your wood's MC is a major clue, at least to me. Your drawn profile looks perfect for the rectangular limb design. Sometimes it's just the luck of the draw with these here wood bows.
Most moisture meters are useless IMO. Go get you a good 7-10 bucks temp/humidity gauge at a hardware store or Wally World. Knowing the correct R/H (between 40-50% for most woods and will give you 8-10 % M/C) where you store your bows/wood is paramount for repeated success.
To get that length bow to open up a little more for a longer draw, you can do as other suggested and make your bow longer. Or change designs. You can shorten the rectangular section back up to about a third and pyramid from there. Keep your tips stiff just like you did with this one. Good luck........Art B
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Good advice.
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I agree with most, the outer third of the limbs not bending much.
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looks like everyone likes to give some advice, so I will throw in my twopence worth ( english saying); firstly. condolences over the break..
its quite obviously bending to much over a too short section of limb.... a little more bend out of the fades and a little more towards the tips , it would have been fine... ie. you need to get more of the limb working....
if you got to half inch off full draw you where nearly there"
I agree about the rubbish comments too
dave
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This bow is simular in design but shorter and quite a bit heavier.like D/M said to much bend in one spot .An even smooth arc help distribute load thru out the entire limb .I would think the outter limbs would have taken on a fair bit of set after being shot in.this made from a maple board!
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@bushboy: The outer limbs did take a fair bit of set, right from the get-go, which is part of the reason why I stayed away from them.
The board was rock/sugar maple i'm pretty sure. The kind of maple you get in the hardwood section of Home depot in Canada.
A lot of good points here, and I definitely think I could have gotten to 30" had I distributed the load better. The board could have handled this tiller at my draw of 27", but not at 30" it seems. A lot to think about next time I have to go past 28". This is my first time doing a longer draw length bow, so it has been a learning experience.
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The outers took set because the mids were over stressed.
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30" is a long pull for that design. Do-able, but everything would have to be perfect.
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A break like that looks like a moisture (or lack there of) problem. The heat treating might have killed it. Go out and bend a nice green sapling and see what it looks like when it breaks. Now get a dry dead branch an do the same . Note the difference. All of the points about design are Excellent and quite valid, but if your bow were made out of green wood ,it would still be in one piece (would be a piss poor bow.......... but would have still bent) It's all about the ballance of design,wood selection, moisture content etc.etc.. IMHO. ....to dry from the heat was the proverbial straw.
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I thought the break looked strange,which is why I included pics of it. Perhaps a moisture meter is in order for next time.
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Bubbles,
I have found that the m/c has been below 5% on wood bought fron Home Depot and lowes. I just don't know how to rehydrate them yet. If anyone on this topic can help please let us know.
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Wood will regain some moisture in humid areas. Canada is typically very dry in the winter months for the most part. MC of the wood will drop dangerously low if you don't have a humidifier on your furnace. If your skin is getting dry ,so is the wood. Get a hygrometer. It will be of more practicle use than a moisture meter. (notoriusly inaccurate). There are charts to tell you what the MC of your wood will be at any give Relative Humidity and Temp. Cooking it just sealed the fate. You can't turn a raisin into a grape by adding water. A plump Raison maybe ,but not a grape. ;) You made yourself a fruit snack! :D. If you make another maple bow now,and don't cook it ,you'll likely get a shooter. Follow the advice already given for design/dimension.