Primitive Archer
Main Discussion Area => Bows => Topic started by: mwosborn on May 14, 2013, 11:06:07 pm
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Working on my 2nd mulberry - this one being a rigid handle, 2" wide parallel limb, tapering to 1/2" at tips, 64" ntn. Had to straighten it a bit and remove a twist - used some oil and heat gun - did this after floor tiller. Continued to tiller out to 27" @ 54#. I shot maybe 10-12 arrows and it had some handshock. I worked the tips a bit and shaped them down to see how it affected the hand shock. Went back out to shoot and on my 3rd shot this happened....lower limb. >:(
Just wanted some opinion on cause. The back was worked down to a single ring - a small ring violation right at the tip past the string nock is all. The tiller was looking good and the limbs were bending evenly. Worked the limbs gently and often during tiller. Using a tillering pulley system and never held the bow at a long draw for more than a few seconds at a time.
I was thinking maybe I worked it too soon after heating and straightening and was too dry and brittle?
It does have fairly thin rings so maybe 54# was just too much?
I borrowed a moisture meter and measured the moisture at 7% in the broken limb. A different piece of mulberry in the same room was 10%. Some hickory laying in the room was 7% for reference. (Not sure if the meter is accurate or not?)
What you think?
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Dude ! I would have definatley put the bow under a 48 hour warm oil soak . I know some bowyers will argue after me 8) about this but it literally saturates and increases the mc of a bows wood fiber . Think about it . The heat gun saps the mousture out . I would get into bow physics but iv'e had a few budweisers and no can do . And a ring violation near the nock is nothing . That can be fixed with a hide glue soaked sinew wrap ( its gunna add mass , but ya know this ) . But iv'e personally never built a heavy weight mulberry . And I personally never chase rings , I leave the back untouched .
But in general thier are lots of factors amigo . I trust your tillering , and in that length what concerns me is the hand shock on a RIGID handle bow . How steep were your fades ? Because you dont want a cliff of a fade . They tend to create more hand shock
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Just saw the pics . Couldn't see them before . I personally have never used a moisture meter , but it's obvious your bow failed from tension first . Did you apply to much heat to the back of the bow ? Iv'e had ironwood bows do this when I heat treat the belly with coals to temper a nice reflex but I somehow get the back good . I think it's over heating . Your fades and gradual tiller look cool . So in the end I think ya sunburnt your bow !
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I broke two in a row by doing a lot of heat correcting and going right to a finished bow. I let them sit for a couple weeks out in the unheated part of my shop now before I string them up.
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It is so hard to just let a bow sit after working it with heat, but your experience is just a good reminder of why you should. How long did you wait after using the heat gun before you started bending it?
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Tatanka, Eric, rps3
You may be right - I did heat it pretty good and may have got the back of the bow too much. Only waited couple of days to start working it. From now on I am going to give the bow a nice long rest after heating AND try and be very careful not to heat too much! Thanks for input. BTW - its too late for bow physics anyway! ;D
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With limbs that thin, heating the belly to 200deg. brings the back up to about 180deg. You'll be cooking both side for sure. They tend to stop regaining moisture after about 6 hours or so. You will still lose about 1-2% MC. which can be critical on a already dry stave. Looks like I'm telling you what you have already figured out. Crappy about the bow, but a good learning experience.
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I like using steam. it was probably just to dry. gotta let them get back the moisture. I think 7% is to low, but Im no expert. 8)
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Or heat and grease treat ! Of course not a good idea if you plan to back it , unless you got a strong lye solution to de-grease it a few times ( or if you like scrubbing your bow with a toothbrush and hot soap for 3 hours ) . On an unbacked self bow TONS of hot ( any oil - bear fat , deer fat , lard , mcdonalds french fries ;D ) while heat treating will do better than soaking a bow in water because oil evaporates at a slower rate than water , thus reducing the amount of moisture lost at the same rate as a water soaked bow ( steam , and I hope I said that right ) . Regardless man , it's not really your fault because you can't " become the bow " and feel how hot it's getting . My advice is build another from mulberry with similar dimensions , chase a good ring , make the mid-limbs and near-grip about 1/4th inch wider or a bit more , and smother the bow in grease before heat treating or whatever . These things happen dude ! If I can i'll post a picture if a D style 56" ironwood bow ( bendy through handle ) that I left in the woods EXPOSED for 1 month and 9 days . And she still shoots cuz I soaked her in vegetable oil for 3 days . Without that the bow would be going 3 days soaking wet from rain and 5 days bone dry . It should have broke . But it didn't
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It's never too late for bow physics >:D . But when it is and thier is ZERO coffee , you better call the physch ward on me because I will be saying some crazy stuff . :laugh:
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Maybe , in another primitive bowyer universe / dimension , bow makers create dinosaur - rhino - alien killin non-mulberry and non- osage bows from rotten ply wood and old curtain rods . :D
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Nightmare didnt need to see this. I had 2 mulberry crack on me after heat treating. Didnt coat with anything, got some help from Matt Wirwicki this one was shellacked before, now have it 50# at 18". Will be seeing this in my sleep.
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ahhh that's nothing, little hot glue and electrical tape and you'll be up and shooting again ;) ...said no bowyer ever
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those two straight snap/crackle/pop lines right angled accross the back look scary. :(
I'm no expert but i'd be wondering if the wood had some emotional problems of its own before you even began to stress it?
but whatever, its a good warning TO ME not to rush through any step and allow plenty time after heat treating.
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Good sound discussion fellas.Sorry about your bow.Looks like a too dry break to me too.I've done that to hickory before too by reheating the same spot too often drying it too far and getting a tension break.That mulberry can have multiple rows of pins accross a limb[even more than osage] which for me is usually where my mullbery bows break.Mullberry is my huckleberry although I really like its' potential.
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Yikes... blew a chunk right out. Definitely a tension failure. Hope you didn't get any flying bits in the head!
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Waiting three days for the wood to regain moisture again and reach EMC after heat treating is sufficient. Especially with those thin limbs, the wood will have reached EMC by the time you started tillering. BUT...EMC is not the same as a healthy moisture content! The kind of tension break displayed does look like a break from brittle wood and/or wood that has a moisture content that is too low. Just the fact that this mulberry probably reached EMC again after heat treating, doesn't mean it has enough moisture in it. What has the weather been like in your area, for the past week or so? What temperature and what relative humidity? I don't trust wood moisture meters, but it seems probable that the wood was too dry.
Tatanka, oil does not replace moisture (=water). You can soak wood in oil as long as you wish, but it does not increase or decrease the moisture content of the wood. You're just adding oil to the water that is already present. However, the oil will absorb part of the heat from the heat gun, and will therefore lower the temperature of the wood and effectively lower it's 'boiling point'. The oil will also hold the heat better than wood, since wood cools pretty rapidly in my experience. I wouldn't recommend soaking a bow in oil, but a few drops of oil in the crooked area will help in heat bending with a heat gun.
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Thanks for all the input gents. No one was hurt when she blew - the middle piece didn't even go very far just a few feet. It hasn't dampened my spirits with mulberry. My first mulberry has numerous knots in the lower limb and still shoots very well - a bit different design than this one as it bends a bit in the handle and is narrower and thicker limbed. Will have a go at it again - plenty of mulberry in the shed. I am still going to be careful with the heating - may even go with steam if I don't have too much straightening to do on the next one. Nothing like experience as a teacher.
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I may be lacking in serious bow physics ( as did all primitive cultures who used the bow ) but regardless , I do find lots of oil extends the life of a bow . So I do it because it works . Simple is better . I even have a video on my youtube channel of a firekilled ironwood bow that survived over a month exposed in the open because of the oil treatments . It's still sluggish , but in the end of the day it makes meat . But in my opinion , this is EXACTLY why I back ANY bow that I can , OR build the limbs wide . I don't build bows for speed , power , or cosmetic look . I simply build them for what they were orginally created for- hunting . Because you can spend 30 hours making a perfect bow that shoots 170 FPS , draw it back , and break it . Or spend 10 hours making a trully primitive bow that shoots 120 FPS and drive an arrow through big game at 10 yards . I know our ancestors didn't give a damn about looks . Function equated to survival .
So with that said , I wouldn't dig too deep in science with something so primitive . Hell , even tape measures and blueprint designs will stir your head up and make you think too much . Don't give up on mulberry . It works . It bends , and shoots . Thier will always be failure with even the most carefully designed project . It's a fluke . And most the guys agree here that it was a tension failure from very low moisture . So ? Don't overheat . Substitute low MC with grease or water . They both work .