Primitive Archer
Main Discussion Area => Bows => Topic started by: Wooden Spring on December 05, 2014, 04:57:39 pm
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I was talking to someone the other day about tillering, and as I'm about to start my first stave bows, my one unanswered question was how to go about starting the bow's thickness... Basically what we talked about can be seen in the sketch I drew below... Is this right?
1) Basically, the drawing shows a cross section of a bow at 1 1/2" wide. Start the limb out at 3/4" thick, parallel to the bow's back.
2) If you want the bow to be less than 55#, then come up from the back 1/4" and scribe a line.
3) Then connect that line to a centerline along the belly, forming a triangle in the cross section.
4) Begin rounding this out to tiller the bow to the desired poundage.
(If you want a bow greater than 55#, start by offsetting 3/8" rather than 1/4" and tiller as before.)
Is this even CLOSE to how you pro's do it?
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Ive never done it that way but I guess that method could work. I just work my limbs down to about 5/8" thick or so while floor tillering. Once the limbs are bending nice and even on the floor go to low brace and remove wood from flat spots then to regular brace height and finish tillering. I probably made that sound a lot easier than it actually is sometimes :)
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I don't thin pros measure the thickness unless they are kind of mass producing board bows.
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I do a 1/2" to 3/8" thickness on harder word (denser) and 3/4" to 1/2" on less dense woods. This is just to get them bending. Then there is still quite a bit of wood that still needs to come off. Just be sure and mark your line accurately. If using a ban saw DONT CUT TO CLOSE TO THE LINE, rasp down to it. In your sketch, cutting at an angle is the way I do it so there is a peak in the center of the belly. Every now and again I will cut the peak off with the ban saw. Hope that helps and wasn't too confusing.
P.S. These are general dimensions that will very but they should leave you with enough wood to play with. They are also for stiff handle section bows.
Matt Kulchak
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What wood will you be using, Wooden Spring? What is your draw length? What weight?
Jawge
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+1 okie and Badger. I couldn't tell you the what the starting thickness is on any stave bow I have ever built. Eyeball it at 3/4 inch or there abouts and then Floor tiller till it's bending good and then get it to low brace and finish it. Don't over think it would be my first advice to you. It's far more simple than that.
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When I'm cutting out a bow blank from a tree stave I reduce it on the bandsaw to about 3/4" to start. I test the bend. If still rigid I'll reduce the thickness to 5/8" and check the floor tiller. If still too stiff I'll reduce it to 1/2". All of the reduction to this point is done with a farriers rasp. From this point on I only use a scraper with some light rasp work where necessary.
When the limbs bend evenly and together and you've hit your intended draw weight at your intended draw length, that is how thick the limbs will be.
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if you build enough bow you start to know what looks right. I thing its more of a feel thing than an actual measurement. Every piece of wood will be different so the starting thickness will vary.
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I rough mine out the same way that has been described, 3/4" at the fades to 1/2" thick at the tips just to be sure I have plenty to work with. That leaves quite a bit of rasping on a 45# bow, but better to start too thick than too thin. Jawge raises a good question about the type of wood you're using. You might start narrower than 1 1/2" if it's a dense wood like osage or go wider if it's lighter wood like maple or erc.
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What M/M ,badger and pat said.i like to have 1/4" thick on the edge. Regardless of the crown for a wide limbed bow and 3/4" for a very narrow one.i never like to reply to a thread when the word expert is mentioned, cuz i'm not even close!lol!
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In response, this is for a hickory bow. I just felled a tree and got 8 good staves out of it, so I'm hoping to turn them into bows maybe by Summer. I'd like to be in the 50# range, but as this is a learning experience, I realyy don't care where it actually ends up, so the 1 1/2" width is really arbitrary.
My main concern is technique. How is thickness on a bow done, and where's the best place to start???
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Reduced,flex at floor tiller,repeat.
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Honestly I haven't made enough bows to give great advice but I think Gordon's build along gives the best visual example of intial thickness to start. Check out his build along where he is laying out his thickness taper. That's what these guys are doing by floor tillering they are bending their bow on the floor and removing wood as needed to establish their taper. I'm assuming they lay out their intial thickness taper some how? You can set up your intial taper like gordon does in his build along or free hand it with a pencil but it's just a starting point. Also the width taper effects the thickness taper as well. This is what little info I have picked up. I struggle with how far to floor tiller checking how it feels on the floor with another bow to have a refrence with weight. I hope someone else will chim in on this that knows more than me or will correct me if I'm wrong.
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It's not done by thickness, it's done by bend :) :)
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It's not done by thickness, it's done by bend :) :)
True, but you don't start out with a 16" thick bow either, and to the untrained such as myself, 3/4" might as well be 16" if you ain't got a clue about how to start.
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You're right, but don't miss the point being made. Take wood off until it bends properly rather than relying on a measurement for thickness. When it is bending right, the thickness is right, not the other way around. You can eyeball the early thickness without ever putting a ruler to it.
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So, I am ok with establishing a good starting thickness. When I rough out a bow, I do just that. I make some sort of thicknessing device (could be calipers, could be vice grips, could be a board with a rectangular notch in it. I rough out to a consistent thickness for drying, say, 3/4" for most flatbows, mollies, and recurves, and 1.5x1.5 for an ELB or whatever. I touch it up when I start working the bow, and then I commit to a front profile and shape it to pretty close, except with wide tips. I have no luck at all marking a consistent thickness line and working down to it. We'll get back to that.
The trouble is, that everyone is right about the rest. From that point on, you just have to listen to the bow. BUT, I have to confess, I suck at floor tillering. I just can't see it, and I can't tell how hard I am pushing on it. Build yourself a tilering tree, or at least a cradle to hold the bow. Now, with a long string on, pull the string with the same force as the draw weight will be. Either use a spring scale and pulley, or hang a weight from the string with a hook.
If ABSOLUTELY NOTHING HAPPENS, you know the bow is too heavy. So remove wood evenly. You can either rasp the belly evenly to rough it up, then scrap[e it smooth, OR, if you are timid, color the whole thing with a dark crayon, and then scrape/rasp/spokeshave, it off. If the bow is way stiff, make 3-4 passes, and put it on the tree.
Now, for the faceted tillering thing. This is correct methid, but not exactly as you applied it. You DON'T do it all in one big step. Take your crayon, mark up the belly, and then get your rasp out. Use that faceted tillering technique to remove wood by removing your crayon marks. At a SLIGHT angle, rasp down one side of the belly, then the other side of the belly, then rasp down the high spot you left in the middle. This is MUCH easier and faster than trying to remove the wood all at once across a flat surface. Each time you do this you will remove 1/64"-1/100" or so, unless you are really horsing on the rasp.
Work this all the way to the fades, leaving them crowned or rounded in the middle, just a bit. At some point, the limbs will bend when you put the 50 lb weight on them (or pull), mostly close to the fades. The tips will move 2", or maybe 3". Are they even ? Does it bend the same? If not, do the limb that is bending less. Since the thickness is the same for the whole limb, the bend should concentrate near the handle. Once you have that even, just chase that bend from the middle out along the limbs, keeping it even.
Get out the crayon. Color the whole belly EXCEPT right near the fades. Mentally divide the limb into 4ths, say. Color the outer 3/4ths, and not the inner 1/4th. Then rasp and scrape that off. Then color the outer half, and rasp and scrape that, both limbs the same. Hang the bow on the tree and puill it with 50 lbs of force (or whatever) Does each limb bend the same amount? In the same places. Mark out any weak spots or hinges using the crayon on the BACK of the bow, and stay away from there for a pass or two. It will be bending a few inches now.
From here on, tree the bow, mark stiff spots with crayon, and then make the marks disappear. After a couple bows, you'll just stop using the marks because you'll get it visually, and can go right to the rasp.
Since I started doing this, the hardest part of the bow is roughing them out without gouging them, or heat treating without getting distracted and burning them.