Primitive Archer
Main Discussion Area => Bows => Topic started by: cryostallion on June 14, 2011, 11:53:41 am
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hey everyone- just finished up tillering on my first red oak board bow, and i was wondering if i could get some other opinions on what to do next with it. first off, i came in way underweight. about 40 lbs at 31" when i was hoping for 50#. before tillering, i backed it with hemp twine, my first attempt at backing of any kind. its not pretty. my first question is- if i do some more backing layers, will it raise the poundage? and is that even safe to do? i have some nice antique linen cloth that i want to put on it. i was thinking i would just glue it on right over the crappy hemp job.
My next question has to do with the massive set i always end up with. i've only made a few bows so far, before this board bow i've used only self harvested white ash. i end up with huge set every time. this red oak has the least set so far, but it's still bad. so, is there any reason why i can't steam these limbs straight again? is there anything else i can do to fix this problem after it's already done?
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The tiller looks nice on the bow,first off how long is it,you may be able to cut it down a few inches
and heat treat the belly and add a little weight, Is the wood good and dry ? Sometimes that will cause the set you are having. 31 is a pretty long draw for a self bow anyway so all aspects will have to be right for you not to get some set and also for the bow to hold up,I don't think the linen will help as far as weight goes. :)
Pappy
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Your tiller looks very good. The excess set is due to overstressing the wood before it was ready.
If it were mine I'd leave it as it is and move on to the next stave. Adding more backing will only add more physical weight which will reduce the cast. You have the tillering part worked out so now work on getting the next one to full draw without overstressing the wood. Take it slow and steady and don't pull it past it's ultimate draw weight or draw length.
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pappy-
69" tip to tip. about 68" where the string cuts into the back. already cut an inch off each end once. i'm afraid to go shorter because of the long draw. so heat treating the belly adds weight? i could swear i just read something about heat treating dropping weight. i read so much different stuff though that i get it all mixed up :P
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PATs right I'd move on. Pappy has point is it well seasoned that and over stressing your limbs are the main reason for set. Which is crushed cells. NEVER draw past your entened draw weight. The only backing which adds weight(poundage) is sinew unless you glue some reflex in to the bow with a wood backing. But this has to be now before the wood cells are crushed. This has to be none before on you'll just cruch the backings cells.
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hey pat-
thanks for the compliment, this was the first bow that i have been happy with the tiller. i feel i was waaaay more careful in the process than in my previous attempts. scraping less wood between tiller tree checks, etc. interestingly, i never pulled the bow even close to the target weight because i was focused on getting it to bend right before i stressed it that much. i *think* i learned a lot about what "bending right" looks like. we'll see with the next bow...
the reason i mentioned putting linen on to raise weight is i just read tim baker's chapter "design and performance revisited" in TBB IV and the part on linen backing ends with this:
"combed linen will allow the cliched impossible: putting wood back on after too much has been removed. a 30 lb bow can become a 60-pounder. not much thickness is needed either. about 1/16" of combed flax on a typical limb will do."
any thoughts???
-Pat R
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hey crooketarrow-
i just did a check of the moisture content. reads about 7.5 right on the surface, and closer to 9 at about 1/8" deep, so i guess overstressing is to blame. i never know what to go by using this pin type meter. just beneath the surface i always get a much lower reading than when i really jam the pins in deep.
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cryostallion, First off great first man, I don't care who you are, most people end up making a 20-25lb kids bow on their first shot. Baker was talking about combed linen or flax, not twisted string linen(flax). big difference. the string has a twist in it which will stretch and unless you can apply it perfectly next to oneanother you wont have the density of combed flax. as far as the set, look at your unbraced pic you can see where it starts to bend is where the set happened, left side looks like mid-limb. you may not have ever pulled it passed intented draw weight but the movement you got was probably in only that spot. don't just never pull past intended draw weight but never pull past where you see a unevenly bending limb.. I still get in a hurry and do just that. again you have it down sweet tiller.
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As strong as flax(linen) is it can cause string follow. It can overpower the belly causing excess stress which leads to string follow.
As you are tillering your bow are you exercising the bend after taking wood off? To me this is important to be sure the wood removal registers. In some cases you won't notice any change after removing wood than all of a sudden you have gone too far.
I think you are right to concentrate on how well the bow bends first. After you have that figured out you can concentrate on removing wood without over stressing the belly.
Are you using a long string for tillering? How far are you going with the long string? Because of the leverage difference in a long string and a short string if you take the limbs out too far before you go to the short string this can over stress the limbs leading to an under weight bow and/or excessive set.
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hey erik, thanks for the compliment but i think you got the wrong idea- it's bow #5. but like i said, the first one where i am at least pleased with the tiller, so thank you :)
i definitely see what you are talking about in the unbraced picture. i hope that i can stay in control next time around and catch those problems...
as for the linen backing, i think you misunderstood- the backing i was thinking of putting on OVER the crappy hemp string one is actually linen cloth, not string. it's fairly heavy and tightly woven. also about 150 years old :)! seeing how linen is so low in mass compared to other backings, and given what baker said about it raising the draw weight, i figured it might be a solution to the bow being 10 lbs underweight.
any more thoughts or advice on this greatly welcomed!
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sorry I misunderstood cryo, linen cloth is great but then you have half the mass of the cloth doing nothing(the horizontal thread is dead weight). I will have to reread that section by Baker on cloth.
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sorry I misunderstood cryo, linen cloth is great but then you have half the mass of the cloth doing nothing(the horizontal thread is dead weight). I will have to reread that section by Baker on cloth.
you are absolutely right man, in fact i just re-read the next page in the book- the section on 'canvas backings' (which is actually what i should have been paying attention to in the first place since that's what i was thinking of using ::))
here's what it says paraphrased:
4 oz canvas backing would take on about 10% of a 50 lb bow's tension load. it would have to be more than ten times stronger to overpower the belly. 10 oz/yd linen takes on about 25% of the tension load- still far short of being stronger than the belly. fabric has much higher mass per tension resistance (being made from twisted threads)than unspun fiber. mass is doubled due to only half the threads working in tension.
i wonder if the tension load would be too much for the belly, since i'd be putting it on over an existing backing of hemp cordage? sounds like the mass might be unacceptable too... darn
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a single layer would probably be fine but it is red oak not known for it's compression strength.
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As strong as flax(linen) is it can cause string follow. It can overpower the belly causing excess stress which leads to string follow.
As you are tillering your bow are you exercising the bend after taking wood off? To me this is important to be sure the wood removal registers. In some cases you won't notice any change after removing wood than all of a sudden you have gone too far.
I think you are right to concentrate on how well the bow bends first. After you have that figured out you can concentrate on removing wood without over stressing the belly.
Are you using a long string for tillering? How far are you going with the long string? Because of the leverage difference in a long string and a short string if you take the limbs out too far before you go to the short string this can over stress the limbs leading to an under weight bow and/or excessive set.
here's one that's been bugging me: is string follow the same thing as set or what?
i have been exercising the limbs, yes.
when you say short string, do you mean low-brace length? i started with a long string that is taut at around the 7" mark on the tree. i get it bending around 10" from there as per george tsoukalis' advice before bracing it.
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I previously typed out a nice long post . Poof. It's gone. You did well. The bow is well tillered. Nice job. The excessive set is caused because the bow is too short for your draw length and there is probably an 8 in non bending handle. 3 1 +31+ 8= 70 in minimum. Jawge
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you could scrape off the flax and glue on a wood backing and induce a little reflex, then retiller to draw weight, personally I'd keep it as is for a target bow and build another bow, Bub
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about 68" where the string cuts into the back.
Please, do not cut notches in the BACK of the bow. You should make string grooves only on the sides of the limbs. A groove in the back can only be done when you apply a tip overlay, but even then you still need to be careful. There's chance the bow will break at the grooves. It's like peeling off the belly half from the back half.
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Please, do not cut notches in the BACK of the bow. You should make string grooves only on the sides of the limbs. A groove in the back can only be done when you apply a tip overlay, but even then you still need to be careful. There's chance the bow will break at the grooves. It's like peeling off the belly half from the back half.
Correct me if I'm wrong, but I don't think that's much of an issue when using quarter-sawn boards for bows. I do it all the time while tillering. Usually tip overlays are one of the last steps for me.
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george- don't you hate when that happens!? >:D
as for the bow, it started out 72" long. i only cut it down to 69" after the tillering had been completed, meaning it definitely had something to do with my craftsmanship, if not everything.
hey bub,
it actually shoots well so i don't think i will try to do any bending...the only thing is the backing isn't pretty. i wish it had the linen cloth instead.
i wonder if it's too risky to scrape off the hemp cord and put the linen on?
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Please, do not cut notches in the BACK of the bow.
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i should have been more clear and said where the string lays across the back of the bow. i didn't cut through the backing, although i suppose it might be alright to on a lumber bow like cam said.
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I'm looking at your unbraced pic and, although I clearly see the set, I don't think it is something to mess with if the bow is otherwise performing well. I'd definitely live with it and enjoy shooting it to the fullest while moving on to the next. Just use it as a practice bow if nothing else. I also read through the posts and there is some really good advice on beating set already written and, frankly, I don't see any room to add anything else.
Good Luck and Enjoy!