Primitive Archer
Main Discussion Area => Bows => Topic started by: Richard B on March 22, 2014, 08:52:29 am
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Got hold of an elm stave. Cut about 18 months ago and dried outside (I think). Moisture content reads about 18%. Nice straight stave with a slight reflex. I debarked it last week and found a couple of things:
1. Where the bark was missing in the middle (rubbed off after felling?) the surface is stained and slightly scratched.
2. In a number of areas there were small holes through the bark (approx 1mm dia) and the bark was chewed away in a way that suggests infection by the sort of beetle larvae that can carry dutch elm disease. The larvae also chewed about 0.5mm into the outer ring of wood as can be seen in the last photo (the lighting exaggerates the depth).
What do people think? Should I remove the outer ring to get rid of the stained surface (which may have degraded?) and the beetle larvae marks?
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Id clean t up by going down a few rings if you can. Im only guessing, but it looks as if it was standing dead when cut.
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Gonna have to chase a ring down to one that is unviolated by cuts and bugs and weather. Pretty straight and looks like a bow is hiding in there :)
Tracy
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Take it down below damadge, shape it, take to floor tiller, and let it dry some more.
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Many thanks for the comments. Am scraping away chasing rings. I think that the wood is clean 2 rings in but I'll know when I get to the end.
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Have chased down 2 rings and found sound wood (may go down another ring as there is a little staining still left on one limb). For layout an thinking of a flat bow 69" NTN. 4" handle (centered on bow) with 2" long fades out to a 2" max width. One limb is pretty much knot free, but the other requires some thinking.
I have maintained a 2" width for 12" and then tapered down to 1/2" at the nocks. The photo shows my thoughts on how to work around the knots on the outer, tapered part, of the knotty limb. The middle line represents the string and passes through the center of the handle and the nocks at each end.
This will be my first attempt at a self bow, so would welcome any comments!
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I'd prob go down another one or two rings until its all fresh white wood...your dimensions sounds fine...if the grain is straight you can draw a straight line for your center line and layout from each side from that..but you should be making your centerline along the top of the crown of the stave faithfully following the grain....it looks like your deviating some from your center line to avoid those knots...its hard for me to see the grain from those pics...but I'm sure the grain flows around those areas..and when laying out the lines on the sides from your centerline you need to follow those as well....now elm might be able to take that subtle violation you have,but when first attempting to build bows it is best to give yourself the best chance at success and follow the grain faithfully to the T...
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Getting close to floor tiller now. One of the knots that I avoided on the back of the bow is still present as a cluster of pin knots down the side and about 2mm into the belly (see photo below). Am concerned that this could act as a weak spot. Any advice?
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I'm a firm believer in the water think super glue from lee valley. I give a couple drops in all my knots and pins, and will hit it more when the belly gets worked down more. Just a little insurance
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How wide is the blank at that spot?
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Have been slowly reducing the thickness of my stave to start it bending. I am now about 3mm over the thickness that I think will give the target weight (55lbs at 28"), however the varying amount of crown makes calculating section properties a bit tricky. The picture shows the bow tillered on a long string to about 60lbs. The ghosted image is the unstrung shape and the blue and red lines are the predicted tiller for the strung bow ans drawn bow respectively. These curves were developed using David Dewey's spreadsheets for the width profile of the bow and are the same curves that I used to tiller the miniature bow I made from the same stave (see other post).
The back of the bow undulates quite a bit (as does the belly- to give an even taper) so I have drawn a straight pencil line to help me see how the bow is bending. I think it is bending quite evenly, although I wont make the mistake of trying to match the predicted strung curve until I am on the short string (doing that on the miniature bow meant that I ended up removing too much material from the inner parts of the limbs, as the shape changed considerably with the short string).
I think I will remove 1mm along both limbs and see where that gets me. This is my fist go at tillering a full size bow so would be grateful for any advice/comments.
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You can paint by numbers, but you cant build a bow by numbers. You're approaching this bow building too technically and too mathematically.
"Moisture content reads about 18%"
"These curves were developed using David Dewey's spreadsheets"
"about 3mm over the thickness that I think will give the target weight"
For me, these are all indicators that you are trying to build by numbers. I understand that you (especially a beginner) need dimensions to get started. But you've surpassed the point where exact measurements no longer work. You can try to lay out the width of the bow very meticulously, but since there are knots and dips in the wood, you need to be creative. You can try to predict a tiller shape with a spreadsheet, but since there are knots and natural variations in the wood, you will have to compromise and create a different tiller in some places. Make sure that you enjoy the process and the woodwork, and you don't have to rely on fixed numbers all the time. If you are enjoying this mathematical approach, then fine. But remember that cavemen didn't have tape measures, spreadsheets and calipers, yet they build fantastic bows.
The bow and tiller is looking good. If the last pic was taken at a draw weight of 60 pounds, you obviously have a lot of wood (thickness) left to remove. As soon as you get a tip deflection (not draw length!) of about 6" at your desired draw weight, you should string the bow to a low brace height. At the moment, you could also shorten your long string, until it is just tight to the handle.
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Fair point, I do sometimes tend to overanalyse. One of the nice things about working with wood is that its properties are too complex to be able to solve the problem by analysis only and you have to feel your way there. The complexities that come with the undulating surface of the back that you get when you follow a ring (which I think are rather beautiful on my elm stave) also make things interesting. But I still enjoy doing the sums and trying to understand what is going on with the physics.
I shall keep scraping away and, hopefully, get to full draw without breaking anything!
One thing I do need to get is a better string. The parachute cord I am using is a bit stretchy.
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DarkSoul, thanks for the lesson! ;)
Richard, what kind of Elm is this? Also have my first stave (Osage) but yours is definitely more challenging. Wishing you well. I'm following this one.
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you've surpassed the point where exact measurements no longer work.
Darksoul is right as usual! The only measurement I actually ever take when I make a bow is to find the center with a piece of string I fold in halves. When I help beginners on theirs first steps, they usually find it very hard to accept this... ;D
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Not sure what sort of elm it is. The draw weight I achieved with the miniature bow suggested similar properties to English elm, but its all fairly approximate with am 18" long bow. The stave was big enough for me to cut enough for the bow, a miniature and enough left over to make up one of the test pieces describes in TBB vol 1. Haven't got round to this but should be able to estimate the strength of the wood, density etc which might help me identify it (there I go, on about numbers again!). Should really do this before proceeding with the tillering, I guess as it would give a better idea of what draw weight I should be able to safely achieve before I go and break it. I am brand new to this and so don't have the experience to be able to look at a stave and assess its strength (also I'm a geeky engineer and like doing sums!)
My most time consuming hobby is building model boats, again with lots of numbers. Have a look at my website and you will see what I mean!
http://richardsmodelboats.webs.com/ (http://richardsmodelboats.webs.com/)
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Richard, send me a PM with your address (if your stateside) and I will send you some B55 or B500 to make you a string.
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Sidmand,
Unfortunately, I'm in the UK, but I think I can buy some locally. Many thanks for the kind offer though.
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Yeah Richard, does sound like you're over thinking a bit on this. I'm new as well. I've broken enough of these to know it's better to go by feel than try to make too much of a science of it. You may be able to engineer using certain materials but this is working with organic variables. It will require you to think differently. Making bows is truly a tactile art.
I don't know if this is true for all woods or with all designs but to get at least a few actual bows completed I approached it this way, and this is speaking in a broad sense:
When you get to floor tiller try to really feel the wood's elasticity. At floor tiller if it's bending a lot while still thick than it's saying it has a weaker composition, so don't ask it to be a heavyweight. If it's getting thin to get to floor tiller than it's saying it's sting and loves to bend so you can ask more from it.
Of course, sometimes there are 'unseen' forces within the wood, a splinter lifts out of nowhere or grain looks great but inside it's brittle (coarse as opposed to dense long fibers), but you won't know until you either go too far or get close to where you're asking it to be which will really only come with experience. You gotta break 'em to make 'em. Part of the game.
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One of the disconcerting things is that it is difficult to know whats inside a stave (without radiography, which would be a bit pricey...). I had a couple of tiny knots on the belly which grew into huge knots as I removed wood. Fortunately they both disappeared completely before I reached floor tiller. With all the uncertainty over the material, and the fact that the difference in the strain in the outermost fibres and the failure strain is going to be small in an efficient bow, all one can do is try to tiller as carefully as possible to keep the strain even and compensate for knots and other flaws as they appear. I suppose that it is this risk/uncertainty that makes creation of a working bow so satisfying. But I haven't got there yet!
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Basic question
The back of my bow undulates both along and across the bow. I have tried for an even taper measuring the thickness at the centerline.
Should I go for the same thickness at each side, which would mean the belly twisting to match the twist (propeller?) of the back?
Also, the thickness of the rings varies from one side to another so that aiming for even thickness across a section can result in the rings running off to one side.
Am I making sense?
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Keep the thickness even across even if it leaves it looking twisted. There is a HUGE difference between:-
1. A bow with twist that draws true and straight (my fave' bow is called "Twister" http://www.primitivearcher.com/smf/index.php/topic,28324.0.html (http://www.primitivearcher.com/smf/index.php/topic,28324.0.html) )
and...
2. A bow with no twist unstrung, but twists (or tries to bend sideways) as it is drawn.
Having one edge thinner than the other is a recipe for number option 2.
If the back is a continuous ring, you adjust the belly to maintain even thickness, of course there are cases where for some reason this won't work or you have to make a compromise. If you have ring violation running along the bow that's not so bad. Sometimes there are several ways to tackle a problem, sometimes all or none are good, and often it's a little of option A with a little of option B,,, it's called "experience"... enjoy >:D
You can use heat to take out the twist if you want to.
Have a shufti at this post in my blog http://bowyersdiary.blogspot.co.uk/search?q=dealing+with+the+dip (http://bowyersdiary.blogspot.co.uk/search?q=dealing+with+the+dip)
Del
BTW the bug marks under the bark look like Dutch Elm disease to me, first Elm bow I ever made was like that, I went down a few rings and it was ok.
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Many thanks Del. I will go with even thickness on both sides and follow the twist on the back. Yes, I thought dutch elm disease as well. Have gone down 3 rings and the back is clean now. There is a very slight staining through the thickness at one end, which I am a bit concerned about. However, I used that end for the miniature bow and it seemed to hold up OK...
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2mm removed from the thickness of both limbs. Thickness is now 19.5mm at the fades tapering to around 13mm at the tips. At the fades the section has about 7mm of crown (i.e. is about 12.5mm thick at the sides). The crown varies along the length of both limbs due to knots on the back surface and some deep blind knots (now dissapeared from the belly), which makes going for an even taper a bit tricky.
Still using the (rather elastic) long sting. Nearly bent enough for bracing with a short string (picture below) pulling 55lbs (target weight at 28"). Both limbs seem to be bending evenly (although a little stiff at the end of the right hand limb around the knot?). Have maintained an even thickness on each side, so the belly twists around following the twist of the back as discussed with Del (above).The tips dont seem to be twisting as the bow bends, so hopefully under control(?).
Probably take another 1mm off both limbs before it will bend enough to brace safely without overloading?
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Shaved another small amount off both limbs and draws another 2 inches with the long string (still at target weight of 55lbs)
Do you think it is ready for a low brace height with as shorter string?
I think the right hand limb is a bit stiff around the knot (near the tip)?
I have some additional width here (having followed the grain around the knot), but a bit nervous about removing too much thickness.
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After a nervous afternoon of tillering, now have the bow at full brace (hard work!, hopefully a bit easier when I have it to full draw) and drawn to 23 inches at 55lbs. Great relief to have got so far without disaster :)! And still have 5" of draw to play with to, hopefully, end up with a nice even tiller at 28".
Nervous about breaking it after having got so far, so would welcome any advice on where best to remove wood. :-\
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Your tiller looks pretty good to me.
You are holding the draw pics statically with the set up you have. Add a pulley and rope so you can stand back, exercise the limbs and hold it just long enough to take the pic.
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This looks very good!
I think, the last third is a little bit to stif, there is much bending near the handle for me.
Looks like it is becoming a great bow!
Benedikt
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Pat,
Yes a pulley arrangement would be good. I guess I would have to fix it to a wall somewhere. Does leaving the bow drawn for any length of time make string follow worse?
Benedikt,
I am trying to match the target tiller curves I have plotted on the piece of paper behind the bow. In theory, this should give me an even strain along the bow for the width profile that I have. I agree, however that the ends are a bit stiff still and I guess I could scrape something off the outer third of both limbs. Its a bit more difficult to judge with the right hand limb which has a few knots and weaves about a bit. I have followed the grain around the outermost knot, as best I can, which seems to have left the bow a bit stiff there. Do you think it would be OK to scrape a bit off the belly there and let it bend through the knot?
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Does leaving the bow drawn for any length of time make string follow worse?
Yes, it does! You're fine at 23" maybe, but it will induce set when you're approaching full draw. From now on, you should no longer use the tiller stick. It's best to use a tiller tree. That way you can also attach a scale and monitor draw weight more easily. If you can't make a tiller tree, you should use the reflection of the bow in a window/mirror when you draw the bow by hand. You could even use the shadow when you're working in the sun.
I can't tell from the pics, but now is also the time that you should make sure all the edges are nicely rounded. Especially the back edges should be smooth and round. Scrape away all the tool marks, if you haven't done so. This could easily gain you another inch of draw length. The midlimbon the right hand side is a bit stiff. Near the knot. Make it bend a bit more, but be careful not to let this knot bend too much. The same holds true for the outer limb on the right side. Since I can't see how big those knots are (there's no recent pic of it), I can't tell you how much the bow should bend there. Remember that the knot itself stretches only one inch of limb length. So if you want to tiller a knot to be stiff, the bow should have a section of only 1" that remains stiff. Not the current 5" as pictured in the right mid limb.
You can go and shoot some arrows at 23" draw length now, but please be very careful not to overdraw the bow! Mark every arrow carefully at 23" (with some tape or a rubber band).
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Hmmm....that's difficult :-\
One the one hand, when the bending is more regular, the bow mabye will have a longer lifetime.
But one the other hand, when the knots get to weak, he could break there.
I would weaken the outer third a little bit, just a few scratches, then check again.
When you have many problem zones in the outer thirds, let in bend more near the handle, so just weaken it a little bit in small steps, like I said.
Regards,
Benedikt
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Reached 28" draw with 57lbs! Well pleased to have hit my target draw weight and my target tillered shape (well, not too far off) with my first full sized bow :).
I wimped out on the knot at the end of the right hand limb, leaving lots of wood around it (sides and belly), which has meant that the tip of the limb is a little stiff.
The second picture shows the bow and the miniature that I made from this stave. Wasnt sure I was going to be able to make something of the stave when I saw the condtion of the surface under the bark.Sting follow is just under 2", most of that gained early on while I thought that holding at draw was a good way to exercise the limbs. Thanks for the heads up on that one darksoul. Will sort myself out with a proper arrangement with a pulley for my next bow. With this one I used a camera with a self timer. Set it off and then counted the seconds off and drew the bow just long enough for the shutter to go off.A bit hectic, but seemed to work OK (no more string follow!). Did that every inch of draw from 23 to 28 inches. Was surprized at how much material I had to take off to get from 55lbs at 23 inches to 57lbs at 28 inches.
Both bows have been a great learning experience. Many thanks for all your help on the way through :).
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That turned out great Richard. I really like it. I like the stiff tips. Looks like a great shooter :)
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That looks awesome! Super fantastic tiller. A++
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Looks excellent :D
I've been hoping it would turn out well for you, especially since I just broke my first elm stave ::)... was hoping you'd show it whos boss ;)
I've started my next elm stave, nearly got the bark off and the back clean, and I think I need to take a page out of your book, and slow it down, be more careful and do a good job this time.
Do you have a plan for your next bow yet?
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You did an excellent job!
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Looks great. congrats!
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Really nice bow!!!
... and even the big one is not bad ;)
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The bow is bending nicely and looks great, real good work on that piece of elm. Now you get to enjoy shooting it as a reward for all the hard work, looks like it will hold up for years. :)
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Nice tiller and really like the character on the back 8) I'm a fan of stiff outers...
Don
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Very nice work! The photo with the miniature is awesome. With the stiff outers and the 2" of follow, it would be a great candidate for flipping the tips. Congratulations on hitting your mark!!!
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Many thanks for the kind comments.
Next plan is to build a set of arrows of varying spine so I can learn a bit about dynamic spine on a non center shot bow (which I find a bit confusing).
I am feeling a bit more confident now to return to making a takedown from the rather nice yew billets I got from Carson!