Primitive Archer
Main Discussion Area => Bows => Topic started by: WillS on January 18, 2013, 10:03:58 am
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Hey guys,
I picked up this piece of English yew which looked stunning before I split it... but it has a really bad corkscrew twist down it's length. It's 72" long, and about 4" wide. I cannot work out how to get anything out of it, as the twist is so extreme that one end will just be all heartwood if I keep it as it is. I have very little experience with steam-treating propellor twist, so probably wouldn't feel comfortable using steam to correct this - plus I just don't know how to cut a bow shape out of a piece like this anyway.
The other problem is that on the end that is twisted, the wood has split into a fork. Running a string line down the back shows that a fairly clean profile could be made with a small amount of twist, but one tip would be smack in the middle of this fork, and the heartwood/sapwood does really odd things here.
Any advice, or just info on what you would do with this would be great! ideally I'd like to try and get an ELB type out of this.
(http://i1202.photobucket.com/albums/bb363/Will_Sherman/WP_000497_zpse4bba218.jpg)
(http://i1202.photobucket.com/albums/bb363/Will_Sherman/WP_000498_zps1322400b.jpg)
(http://i1202.photobucket.com/albums/bb363/Will_Sherman/WP_000500_zpsf4569f6c.jpg)
(http://i1202.photobucket.com/albums/bb363/Will_Sherman/WP_000501_zps3bf1d198.jpg)
This is the fork at the bottom. Don't particularly want to chop off any extra length if avoidable?
(http://i1202.photobucket.com/albums/bb363/Will_Sherman/WP_000502_zpsd8aafa45.jpg)
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That doesn't look to awful and unworkable....if your not ready for it then set it aside and build your skills up more until your ready to tackle it. Layout is easy....just layout a bow along the back following the grain and twist...you don't layout a bow continuing straight thru the twist....like I said set it aside till your ready if it looks too daunting to you.
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Since you dont really know how to continue? I say continue and start to learn so next time you run across a stave as such your not intimidated, but excited to make a bow. Dry heat will straighten it out, twist isnt a problem until the bbow unbraces itself. Start building and go slow. Always consider what your doing and how it will effect the build in its later stages.
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Cheers for the replies! I'm gonna give it a go, as there's nothing to lose!
Still not sure about laying out the bow though.
....just layout a bow along the back following the grain and twist...you don't layout a bow continuing straight thru the twist....
This doesn't quite make sense to me? I can't figure out how to layout a bow profile without going through the twist? You can only draw out a guideline onto the bark, and that can only be in one dimension. When I come to cut it out, whether it's with an axe or planer etc, as the wood twists suddenly there will be too much sap or heartwood in the twisted portion right? How do you get around that?
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What Blackhawk is saying is to draw the bow on the back so that it follows all the dips, snakes and twists. Unless the stave is perfectly straight you cant have a perfectly straight bow. So as you draw your center line it cant veer off the side of the bow just because the stave is twisting it has to follow the center of the stave which happens to have twisted off to the side. Try to imagine if you were able to magically wrestle the stave perfectly straight, then you drew out your bow and then your stave popped back into it's current twisted shape, that's how your layout should look. I hope my ramblings make sense, it's harder to describe than to show. If you do that then your heart/sap wood ratio should remain consistent throughout the bow.
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I think that sorta makes sense, thanks! The trouble with being inexperienced I guess is being able to visualise the layout in 3d. I can't quite see it unfortunately!
The stave is straight, front on. It's only in perspective that you see any twist at all. Drawing a centre line has to be done front on, so it will look straight. Trouble is, the wood underneath it won't be square, it will propellor twist. I still can't work out how to cut it out to ensure sapwood/heartwood ratio stays equal.
Frustrating!
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+1 for what Blackhawk said.
Let the grain guide you, but you don't have to follow it slavishly.
I think laying out slightly diagonal and ignoring the twist will be fine.
Del
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If you chop away some of the twist from each edge at the ends, it will help you see it as straight and lay out a line.
Eg. Make it look like it would if you'd sawn it on a bandsaw.
(Dunno if the pic helps?)
Del
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What you gotta do first is establish a centerline. Scrape the bark off and follow one single longitudal grain. Once that is done layout your bow to the center line. Forget about it being straight for now as long as it follows the longitudal grain exactly. Then as you cut out the bow keep the sides square to the back along it's length. This means as the stave twists you have to be careful to keep the sides from cutting into the belly. Maybe leave the areas with the most twist a little wide for your initial cut then come back and true them up with the back while cutting to your line more closely. Hope this helps. Try not to over complicate it by visualizing it in 3D. Just follow the grain and do it as you would with a straight bow. When your done, build a caul and get a heat gun and some clamps. It's not as hard as you would think ;)
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Layout will be done with a pencil and steady hand, toss the rulers and meter sticks out for this. Nothing is straight or square on this stave.
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+1 for pearls advice, you have no use for a strait edge. The only thing you may want to know is about how wide the limb should be. but that comes after the center line. I use a strait edge often because im working with boards often. I dont really use a strait edge for something that twists and dips and curves
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Is there enough wood to split it again, going through the center of the fork so each half has one section of the fork at the end? At 4" across you should have enough.
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i have some yew seasoning in the attic almost exactly like like that. that black centre line (heartwood) on the belly of the bow would be good to follow as it runs perfectly with the grain you would just be working from the belly instead of the back, just set the bow out as if that was the string going down the centre of the bow. following it which ever way it twists, once you have the bow shape you want then start reducing and straightening. thats how i plan on doing it. but im far from an expert.
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All brilliant replies! I must have been blinded by frustration earlier! Reading through these again its very clear. Thanks guys!
One final question - if i were to follow the black heartline on the belly (or close to it on the back) what do i do on the fork? I'm not hugely optimistic with splitting it again, as there are some knots to avoid, plus i split the other half again and it wandered around and rendered that piece hopeless apart from billets. Do i follow one of the offshoots of the fork and heat straighten, or go straight down the middle of them both and hope the wood behaves itself?
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When was this wood cut? IMHO if its not at least a year old I would set it aside...yew is the only wood that is just not worth quick drying...especially that piece..because it'll twist,warp,and deflex worse than it is now....and you'd have even a bigger mess to correct.
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It's well seasoned. A good couple of years at this point I think.
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That's why I use a bandsaw to split yew logs. At this point however just rough out the bow and then take out the limb twist using dry heat.
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That fork at the end will end up on the tip of the bow and will probably be unbending so I would just follow the center line and not worry about the fork.
Other than that, what everyone else said.
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Argh!! So I've scraped and peeled the bark off, ready with pencil in hand to follow a single longitudinal grain line... and there aren't any!?!?
I have a piece of ash here which shows quite clearly the vertical grain lines running the whole length of the stave, but there definitely aren't any of those on this piece of yew. It's just one single solid creamy back with apparently no grain anywhere. This doesn't make sense to me, as obviously there are grain lines in the wood, but I definitely can't see them, no matter how bright a light I use (the sun didn't help either)
Usually when I rough out a longbow, I have a template that I use. I lay it over the back, draw around it, and axe or drawknife to the guidlines. Everybody on this thread has said to follow a single line of grain along the back, but what do I do if I can't see any?
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Draw a line down the center of the crown of your stave...since you split it out it'll basically be in the middle of the stave in most cases...and that will be your center line ...templates are only good for boards in most cases
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Ok, that makes life a bit easier. There is however this chunky ol' knot sitting almost dead over the crown, and it would be smack in the middle of the working limb. It's a bit too wide I think to place in the middle of the limb, but to avoid it completely I would have to deviate quite a bit from the crown. Is this a problem? I guess I can probably just heat-straighten that one area if need be?
The black line is where the crown of the stave is, and the red lines are where the edges of the bow limb would be.
(http://i1202.photobucket.com/albums/bb363/Will_Sherman/asdas_zps08dde985.jpg)
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Is this a problem?
No, it's called a challenge :D
That is a pretty nasty knot cluster, in all honesty. You can't ignore it, since it'll be in the limb for the most part. You can't avoid it either, because there is not enough wood on the upper side of it in the picture. The good news, it looks like a solid knot. I think I'd personally choose to keep the width of the bow basically as you have outlined. Leave the bow slightly wider and slightly thicker at the knot area, to make this spot stiff. This will compensate for the weakness that the knot causes.
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If it was possible to avoid it (the photo doesn't quite show accurately how much wood is left on that upper side, and there is a bit extra to play with) is it ok to swoop around the knot, then heat-straighten it back into line?
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Not sure about your yew but with the yew we have here, clusters are no problem. The lumpy yew I just finished was riddled with clusters just like that. Mid limb and even right out of the fades.
(http://i30.photobucket.com/albums/c326/bornagainprimitve/DSC_0072-2.jpg)
(http://i30.photobucket.com/albums/c326/bornagainprimitve/DSC_0063.jpg)
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I'm not too worried about having the cluster in the limb, if that's my only option. It would be nice to avoid it somehow, as it's the only knot that would appear in the entire bow. I don't want to slice through it, as that would almost certainly result in some dangerous sapwood violation on the edge of the bow.
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What gordan said...bandsaw. ;)
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I haven't read all the replies, so forgive me if this is redundant...perhaps you could cut the stave in half, split (or cut, preferably) each billet in two and splice them together. If you've got enough wood in the right places, you could probably get two bows out of it. That will help to reduce the severity of the twist (as you're dealing with half the length) and create a somewhat symmetrical, bookmatched limb profile when all is said and done (which, incidentally, will be easier said than done :) )
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The thing that always catches me out with yew is pulling up grain because its self soft, especially around knots.
Files, rasps, etc are the way to go, planes and drawknives are asking for trouble on all but the cleanest bits.
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Hope you guys don't mind me asking so many questions - really wanna get this right!
Ok, with the issue of marking out the stave sorted, I've reached the point where I need to decide what to do with this tricky fork at the end. It's about 10" from the tip, and splits into three. There are three clear heartlines, and I'm not sure which to follow when laying out the tip.
This shows the heartlines forking into three.
(http://i1202.photobucket.com/albums/bb363/Will_Sherman/WP_000506_zpsc9318ce2.jpg)
This centre heartline turns into kinda fluffy obscure sapwood, and I don't think there is any heartwood underneath it. But as somebody mentioned earlier in the thread, it's not doing much bending this far into the tip, so may not be as important.
(http://i1202.photobucket.com/albums/bb363/Will_Sherman/WP_000507_zps89838ca5.jpg)
And this shows a clearer picture of the three separate forks
(http://i1202.photobucket.com/albums/bb363/Will_Sherman/WP_000509_zps0afa66ca.jpg)
I think I'd rather take the left-hand heartline as my centre line, as it looks far more solid. However that would mean heat-bending the tip back into line with the rest of the stave. While this isn't a problem in practice, it would mean that I would have to bisect the other two heartlines right where all the bending will happen. Would this weaken the bow here?
Sort of like this I suppose
(http://i1202.photobucket.com/albums/bb363/Will_Sherman/Untitled-1_zps2b388b6a.jpg)
Black line would be the centre line of the bow, red lines are the intended outside edges, and blue crosses are where the other two heartlines would be sliced through, with the blue circle the meeting point of everything. How artistic!
Apologies for reviving what is probably a boring thread for you guys who know what you're doing - I'm probably overthinking this and should just get on with it! Many thanks for any tips or advice!
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You don't draw a centerline on the belly along the heartwood pith line...you draw it on the sapwood back...don't worry about where that pith line runs...it usually differs from how the grain runs on the back on the sapwood...and you want to follow that grain because that is where your tension and bow will be,not where the pith is.
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Ace. Thats what I needed to hear, cheers!
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Does the sapwood side have three buttresses matching the three pith lines?
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Sort of, yeah. It has the two outside buttresses, but the middle pith line is weird. Looking straight at the end face, you get the two outside half-circles, and between them there's just a crease or V , with lots of sapwood. Bit like this I suppose - OVO
I've ended up going more or less with the left buttress as it's the straightest, and on the back looks the most solid.