Primitive Archer
Main Discussion Area => Bows => Topic started by: Zedd on December 28, 2016, 11:17:33 pm
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Finally, after lurking here (yeah, I'm one of those fellas) for years I took the plunge and made my first bow. First, I have to thank all the thousands and thousands of tips and advise given on this forum. It is amazing how folks are so willing to share information so readily for so little money....
The bow I decided to make was a home depot red oak board mollegabet bow. I had to go to many different home depots, loew's, and other shops that sell timber, multiple times to find a board with a proper (I think) linear grain structure. I have shot the bow 30-40 times and it seems to be holding up fine (my first consideration). When I realized it wasn't going to blow apart on my, I started to enjoy it. Wow. I mean, wow. I have a 50 lb samick sage recurve, and this mollegabet bow is much much much smoother than that bow. Not trying to disrespect the sage, just saying. Here are the numbers on the how it ended up:
47#/28"
65" ntn
1 3/4" string follow
rawhide backed with a cobra skin on top
Pulling this back was so smooth, I immediately checked the pull weight several times. (The scale was calibrated by picking up several 50 lb bags of fertilizer at the hardware store and surprisingly it was spot on). I can't feel much in my hands even on bows I have shot other folks say have hand shock, so I can't address that, but at 30 feet I was hitting 5 arrows inside a 6" circle. Anyway, my son picked out the skin. I have read and realize there is a risk the TBIII might not bond tanned cobra skin (personally I find the cobra skin a bit gaudy, but hey, no accounting for taste) to the raw-hide adequately, but honestly, I don't figure my son will be shooting it a lot anyway. Question...does anyone have any input on using tanned leather as a backing, or is my understanding correct and this is risky? Here are some pictures...
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I loke it a lot!
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Thank you for the kind comment!
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All of the bend is at the fades. Get the rest of the "working" portion of the limbs bending evenly and together.
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All of the bend is at the fades. Get the rest of the "working" portion of the limbs bending evenly and together.
A sense of proper proportion is obviously not something I am familiar with yet. So, if I were to make the ovals with the foci closer together so the oval becomes more 'circle' like, the limb as a whole would work better? The belly and back of the working portion of the limbs are currently perfectly parallel. Doing this would mean making the middle portion between the two fades slightly thinner than at the fades. Am I understanding you correctly?
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Get rid of the ovals and circles, get a six inch straight edge and use that as your guide. You should have a even gap between the belly and the straight edge then the tiller will be correct. Where is the set anyway do you have a unbraced pic?
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Bubby - the limbs are parallel width - the tiller should be elliptical. The set is at the fades from what I can see so yes a little overstressed there but this is a first bow :) Well done.
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Mike the profile doesn't change the fact that a gizzmo or a straight edge especially with a board bow will give a proper tiller. That said this is a tough first build design i hope i didn't come off too harsh good job so far but tiller could use some tweaking
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I'll see if I can't get picture of the bow laying flat on a table. I appreciate the feedback on the bow. Can't get better if I don't know what is wrong and how to correct it. Bubby, geometrically speaking, the sagitta of a chord moving across an arc (i.e., the gap between a strait edge and the curve) will be constant for a circle but variable for an ellipse. My understanding was that for this type of bow, the tiller should be more elliptical than for other types of bows. Granted, I see how a 'fatter' ellipse will move more of the work into the limbs. Are you suggesting the tiller should be circular?
If someone wanted to know what a straight tiller looks like @ 7/16" with backing is, here you go.
I am thick skinned enough to accept the critics while recognizing not only did I make a functioning bow, but a rather handsome one as well. I am very pleased with my first try.
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I would have been stoked if my first bow looked like this. Mine was only worthy of firewood, and the fire didn't even want to burn it. This is a tough design to start with.
As far as tiller, the tiller should be elliptical, but the bend should increase as you move out on the working portion of the limbs. What you have is an ellipse, but backwards, is bending the most aybyhe limbs, then decreasing as you move out. To see it, use a single ellipse for both limbs, instead of a single one for each limb. If that makes any sense.
Great job, you have a bow that you should be proud of. Now, start your next one.
Eric
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I would have been stoked if my first bow looked like this. Mine was only worthy of firewood, and the fire didn't even want to burn it. This is a tough design to start with.
As far as tiller, the tiller should be elliptical, but the bend should increase as you move out on the working portion of the limbs. What you have is an ellipse, but backwards, is bending the most aybyhe limbs, then decreasing as you move out. To see it, use a single ellipse for both limbs, instead of a single one for each limb. If that makes any sense.
Great job, you have a bow that you should be proud of. Now, start your next one.
Eric
Thanks, I am pretty excited about it. Is this what your talking about?
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Eric,
What do you mean by " is bending the most aybyhe limbs?
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Zedd elliptical or circular tiller the gap between the straight edge and belly should be even, a circle tiller may have more gap than ellitical but the gap should remain constant. I don't need geometric theory to know that if that gap isn't consistently the same the limbs aren't working equally from fade to fade
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Sorry, I should have proof read that. I meant to say is was bending most at the fades, then progressively less outward. Yes, that's what I meant by a single ellipse. Your ellipse should be a bit smaller, it shouldn't go out into Non bending portion of the limbs. The circular and elliptical tiller refers to only the bending portion.
Eric
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What bubby said is very useful method of determining you tiller. I have trouble seeing elliptical tiller when it's subtle. If you run the straight edge across the belly. With an eliptical tiller, the gap will gradually get larger as you move out on the bending portion of the limb. With a circular tiller, it will remain the same.
Eric
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I have trouble seeing elliptical tiller when it's subtle. If you run the straight edge across the belly. With an eliptical tiller, the gap will gradually get larger as you move out on the bending portion of the limb.
Yep, that helps me too.
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Zedd elliptical or circular tiller the gap between the straight edge and belly should be even, a circle tiller may have more gap than ellitical but the gap should remain constant. I don't need geometric theory to know that if that gap isn't consistently the same the limbs aren't working equally from fade to fade
I apologize in advance as I can be pretty hardheaded in that it takes a bit to sink concepts into this thick irish skull of mine. You have given me something to think about. I was a nuclear technician in the Navy and the training has followed me my whole life. One of the consequences is I tend to over think things... That being said, I can think of a couple situations where what your describing would not be the case, however, I don't know if they would apply to this situation. What you are describing is a circle. If 'working' is defined as moving equally throughout the power stroke portion of the limb (pretty obvious where this would be on a mollegabet), then I did not do this. Am I understanding you correctly that you are saying an evenly bent or circular tiller (which is what that method would give) bow means the stress on the limb will be equal throughout the bend? Given two factors, the levers of the outer 1/3 of the limb and the support the fades will give to the working portion of the limb, I am sure this is not the case. That doesn't mean you are wrong in suggesting how to check my tiller though... I am not trying to be argumentative, just trying to understand the stresses on a this type of bow so I can minimize the chance for a catastrophic failure in the future (though this does shoot fantastic now).
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Ok Eric, after looking at what you said, I redid the ellipse and it seems you are suggesting a tiller a bit at the shaded in section here?
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http://www.primitivearcher.com/smf/index.php/topic,23134.msg311835.html#msg311835
Build one of these it will take care of the problem
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Yes! That is exactly what I meant. You can see it perfect with that drawing, and where you have red marks is where it need to bend most.
As far as what you said about stressed. The idea is to keep stresses even throughout. When limbs are parallel, the limbs in theory are thinner the further you progress out, thinner would can bend further than thick would, so your stresses are still "equal," when limbs are pyramids, the thickness is the same, so bend must be even, circular, to keep stresses equal.
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This is the difference between book smart and hands on smart! I have read these pages thousands of times, and only now after seeing what you two fellas are talking about do I understand. It makes perfect sense now! Eric and Bubby, thanks for your help. So on this bow as it stands, the highest stress level would be at the fades nearest the handle because they are working or moving more than the rest of the limb?
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Glad to help. It's awesome would it just clicks.
Yes, so right now your limbs are being stressed the most at the fades and not sharing the stress with the rest of the limb. This can cause excessive set where you least want it.
Eric
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When you say fades, you are referring to the fades near the handle? What is the fade where it goes to the 1/3 outer part of the limb called?
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I was hoping someone could answer the question regarding the use of tanned snake skin as opposed to raw (untanned) snake skin for use as a second backing? Also, since I am going to do at least a couple more board bows before I plunge into the world of the stave, how much leeway do I have regarding the run-off on a red oak board, keeping in mind I will be backing it with rawhide? Finding a board with no run-off and the correct grain orientation is very challenging.
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I've used tanned skins before i soaked in dawn soap water and rinsed no problemo
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very nice bow, especially with the white cobra skin. As for a recommendation for the best glue to use with the rawhide to snake skin joint, you might consider a contact type, rubber cement. Leather workers often use barge brand.
It is hard to prescribe a certain amount of runoff as acceptable, but I would look to minimize runoff angle, especially in the highly strained portions of the limb, and be looking for a board with high latewood ratio, or at least consider other ring orientations besides flat, if using red oak or another ring porous wood. Raw hide as a fix for excess runoff is debatable. Certainly better than a something thin like a cloth backing, but not a cure.
sagitta is latin for arrow :)
Ultimately, when tillering any bow, the appearance of set, early on in the tiller process, is the hands on way to ascertain the working limits of the wood. Although I can appreciate the technical understanding of stress and strain when fleshing out a design, when tillering, I find that tracing the back curve of the just unstrung bow very helpful to learn where the wood is heading towards becoming overstrained.
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I've used tanned skins before i soaked in dawn soap water and rinsed no problemo
That's exactly what I did, I even used Dawn! Thanks. They seem to be holding up ok. I trimmed the skin off flush with the edge instead of rounding the edge off. It would definitely look more polished with a rounded edge and I think the skin will have much less risk of lifting up.
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very nice bow, especially with the white cobra skin......
....Ultimately, when tillering any bow, the appearance of set, early on in the tiller process, is the hands on way to ascertain the working limits of the wood. Although I can appreciate the technical understanding of stress and strain, at least with design considerations. When tillering, I find that tracing the back curve of the just unstrung bow very helpful, when set first becomes detectable.
Thank you. The skin is actually a metallic steel or silver color. It was very shiny, like you could use it to warn away aircraft shiny. I stained it with a coffee brown stain I had from an old job and it took some of the sheen off. I am more a natural color kind of guy.
I don't understand the last part about tracing the back curve. How does tracing the back curve help? Again, my ignorance is showing.
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Congratulations for the incredible first bow. Even for a Mollegabet style bow, the easiest way to tiller the working limb is to give it pyramid front profile. Maybe next time.
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Congratulations for the incredible first bow. Even for a Mollegabet style bow, the easiest way to tiller the working limb is to give it pyramid front profile. Maybe next time.
I might even look more graceful.
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I lay the bow on its side and trace the curve of the back, unstrung, before I start tillering. Of course if it's is a board bow, then I have drawn, pretty much, a straight line. After bending the bow on the long string, or after immediately after un-stringing if it has been braced, I retrace (overlay) the curve again, in order to see precisely where along the limb the set is occurring. It is not enough to just gauge the overall string follow from the position of the tips. Knowing just where the set is occurring tells you much about where (or not) to work so much. These tracings are especially helpful on a stave with natural humps and hollows, but the technique works equally well on a board bow with working limbs that are not equally strained throughout. Assuring that the set happens where you want to, helps you optimize the design. Some will advocate for more set further out on the limb, rather than close to the fade, although with a short working limb like the mollegabet, having the set evenly distributed along the working limb might be the best you could hope for.
I use freezer paper taped to a piece of plywood, with two fixed stops for the tips and use a circular gage block with a sharp pencil to follow the limb.
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I used a tan skin once. I wont do it again. I cleaned them with antifreeze if I remember right. What I don't like about the skins I used is that they seem to change color when the bow gets wet, appearing to soak up and hold water, and that's the last thing you want, especially if over sinew.
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I used a tan skin once. I wont do it again. I cleaned them with antifreeze if I remember right. What I don't like about the skins I used is that they seem to change color when the bow gets wet, appearing to soak up and hold water, and that's the last thing you want, especially if over sinew.
Thanks for that information, I will keep my eye on that. My real passion is making split bamboo fly rods and have used a wonderful wood penetrate/conditioner/sealer from Daly's called Ship n Shore. I have used these Ship n Shore finished bamboo rods in all kinds of weather from hot steamy Texas summer days to sleaty and snowy miserably cold days wade and kayak fishing for striped bass and have never noticed any kind of absorption of water on either my bamboo or my grips (both cork and ratton). Besides leaving a lovely, natural looking flawless finish, Daly's claims Ship n Shore hardens wood 14-25%. (I have no stake in Daly's other than a happy customer). Daly's says Ship n Shore only needs two coats, I put four on mine (and on the split bamboo rods I dip the rods for 24 hours with never a glue failure).
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Rps3 anti freeze is what you tan skins with not clean them, the glycerine is qhat soes it
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Well bubby, I either handled them wrong or remembered what I did incorrectly. I know I did a lot of research before I used them, and I may be a bit confused. They have stuck to the bow real well after heavy use, which was my main concern , but still have that color change when the bow gets wet.