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Crossbows - Everything about Building, Modding, and Using your Crossbow Gear

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    yew and sinew prod help needed

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    stuckinthemud1
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    Post by stuckinthemud1 Fri May 04, 2018 3:58 pm

    Hi everyone!  I have roughed out a yew prod 27" long from a 2" wide stem.  It is 2" wide and 22mm thick at the centre, 1" wide and 18 mm thick at the current tips - I intend splicing horn nocks into the ends.  It has 5mm reflex but I plan on deflexing it a few inches and sinewing.  It does not move at all at the moment, even with all my body weight on the tips.  What is a useful draw weight to tiller to and how much movement should I be looking for? I have built a number of long bows and made a couple of mini crossbows but this is my first 'proper' crossbow so any and all tillering advice will be gratefully received. At the moment I am thinking of using 9" bolts, is this realistic?
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    Post by OrienM Fri May 04, 2018 5:58 pm

    Maximum draw weight will be determined mostly by the method you use to cock the bow; will you be drawing by hand, pulley rope, or...? In my experience heavy wood/sinew prods will be pretty stiff, near-impossible to flex very far by hand or with body weight.

    You will likely be able to get a draw length (brace + power stroke) of about 1/3 of the total, so 9" should be about right. I'd go a little longer (maybe 10-12") on the bolts themselves.

     Personally I used a pulley rope, along with a simple jig to tiller my last few prods. The most recent ended up drawing about 200#, near the maximum I can pull with the rope. I don't tiller at all before sinew is added, and tiller as little (and as carefully) as possible on the jig to keep draw weights high.

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    Post by stuckinthemud1 Sat May 05, 2018 1:48 am

    Love the jig, that's very clever, thanks for the photo I'll make something similar but how did you knot-up the stirrup?  That is super-cool!   
    I put calipers across the prod, my thickness tapers are 24mm at the centre 3 inches (1.5 inch each side of centre), then reducing by 2mm  every 3 inches constant taper to the tips; do you think they will work out OK?
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    Post by Geezer Sat May 05, 2018 8:16 am

    For bolt length: consider going longer, say 14-15 inches.  Very short bolts will fly just fine, but they will tend to bury themselves in the target, deep enough to screw up the fletching.  That means you'll be constantly refletching/repairing bolts.  Making them longer will protect the feathers/vanes because the bolts will stop before the feathers get buried.  (how do I know this?  I tried it of course, with 10 inch bolts) Geezer.
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    Post by OrienM Sun May 06, 2018 12:52 pm

    Your tapers sound reasonable to me; of course it's always a bit of a guess until it can be actually drawn!

    The stirrup on the jig is just a length of paracord, maybe 20' long. After passing back and forth around the limbs a few times to form the stirrup, the working ends were used to whip the strands together, starting at the prod on each side and meeting in the center. The whipping is a 'coxcomb' pattern, just repeated half-hitches, but alternating direction each time.

    I was very worried at first that the cordage stirrup would break at full draw... Shocked. However, in the end it proved more than strong enough to do the job.
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    Post by stuckinthemud1 Mon May 07, 2018 2:50 pm

    Thanks for all that, it's going to be really helpful. On another  note, I've started roughing out the stock and the apple  branch I'm using is slightly curved which could well result in my stock having  a tiny u-shaped profile along it's length. I have noticed several historic stocks with a similar profile, is this a result of manufacture (deliberate), warping or wear-and-tear or all of the above? Any one know?
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    Post by Dark Factor Tue May 08, 2018 11:35 am

    Can u show a picture of the shape of the bow? You speak about general shape or U-cross section? (not so good in english, so I'm not sure to understand).
    The best for bow is a reflex shape, which mean the bow is curved at the opposite side of the one it will have with the string. So when you put the string, the bow has a larger prestressing which give more speed to the arrow/bolt. But reflex gives more stress to the bow and so more risk to break.
    At the opposite, the deflex bow has less stress, less risk to break but slowlier shoot at identical draw weight.
    In bow making, the maximum draw weight is fixed by the user (what he can use), so reflex bow is clearly the best, so we prefer using curved branches if possible. For crossbows, with bending triggers, that's maybe not the same.
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    Post by stuckinthemud1 Wed May 09, 2018 1:50 am

    Alright, things are still very early on, the prod is close to being ready for deflexing before I sinew it but I will finish roughing out the stock so I can be confident it fits - the dimensions of the stock are really marginal - I might have to make do with a 1" nut as I'm not convinced I have the meat to go to 1 1/4".  Will be very happy to receive all comments and advice.  Stock is still being worked by hatchet so things are literally a bit rough.  The line of the floorboards should show the dip in the back of the stock

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    Post by Dark Factor Wed May 09, 2018 10:22 am

    Yes, your bow is curved on his side... I thought it was on the other direction.
    That's a problem when you make a "hand" bow because it turn on your hand, but for crossbows, I think that's better so the string is straighter and slide better on the tiller.

    I rarely make sinew backed bows, but that's generally better to make a quick tillering before putting sinew. Also, that's important to take out the darker part of the bark still on your bow before you glue sinew (not important at all if you make selfbows) because on some wood species, this will go out naturally... with all the sinew glued on it. (If it's really yew, I advice you to take out the darker parts, because it will go with time)

    You already have your sinew? how long they are?

    Personnaly, I "love" drawknifes. hatchet and other tools (even moderns) don't works as well as a good drawknife to make bows... but others can think differently too.
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    Post by stuckinthemud1 Thu May 10, 2018 1:32 am

    Yes, I will be taking the top layer down to the sap-wood. The sinew is buffalo back sinew but it is cut into 15cm lengths so I will be overlapping the lengths and laying down 3 layers.  I don't have a problem using power tools, I would love to have a big band-saw, but I very much prefer using hand-tools for most work, though I confess my Shinto rasp is used much more than my draw-knives for bows and such-like.
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    Post by Dark Factor Thu May 10, 2018 2:58 am

    Everybody has his favourite tools. The result can sometime be different according to the one you use, but it it works for you, that's good.

    Yes, sinew is rarelly long. that's a pity they cut back sinew because that's the longest. I've tried deer leg sinew and it was about 15-25 cm long.http://www.licorneargent.be/les-arcs/facture-experience/fabrication-arc-composite/6-preparation-tendon/
    For a crossbow bow, this will be easier because it's short, but for longer bows, the longest, the better.
    You must put layers of sinews like a brick wall. Yes, minimum 3 layers, but it depends the thickness of them. Generally we consider the sinew part of bow must be at least 1/10 to 1/7 of the thickness of the total bow. This can be more for more security and if you want a very strong bow.

    honestly, sinew isn't something I like to glue, so I rarelly do it. and it demands hours to hammer the orginal tendon + hours to glue all... it's good to try once or two, but longest materials are much easier to use.
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    Post by OrienM Sat May 12, 2018 8:29 am

    Your wood pieces look good...the stock/tiller piece is kind of marginal in size, but should work fine. The bend to the right shouldn't hurt anything, assuming you are right-handed; I carved my last tiller that way on purpose for a better sight picture.

    Prod also looks good...definitely remove any trace of bark, and roughing up the back surface before gluing sinew won't hurt, either.

    Personally, I prefer leg sinew to back, despite the shorter lengths; leg sinew is finer, and packs down more tightly. Back sinew is a bit wiry, and can leave gaps between the strands if you aren't careful. You may want to wrap up the sinewed prod to compress it while it cures, using an ace bandage or similar.

    You'll get better bonds between layers if you don't let the surface dry out completely before adding the next layer; I also recommend touching the sinew-back as little as possible, as hand oils will impair gluing.
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    Post by stuckinthemud1 Fri May 25, 2018 2:44 pm

    Just a swift progress update; the stock is about 2/3 carved and I'm starting to play around with patterns for the veneers and horn pieces.  The horn should be re-sawn next week and the bone cut to size, all being well that is. Any/all comments welcome
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    Post by stuckinthemud1 Thu Jun 07, 2018 1:34 am

    I have found a blacksmith who is very keen to help with this project and so have a couple of questions about the metalwork: I am trying to stay close to dimensions used in the 14th century, I think the tiller at the pivot point will be about 8mm thick? What would the dimensions be at the sear?  Also, what diameter should I be aiming for for the pivot-pin?   Regarding the stirrup, I am planning for a circular stirrup, but have no idea for the dimensions needed.  Thanks in advance :-)
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    Post by stuckinthemud1 Sat Oct 06, 2018 4:40 pm

    Ok, small problem, I've got the prod moving, but a two handed pull only gives me about an inch and a half of movement.  How much mechanical advantage do the various levers give? That is a wippe or a goats foot or a belt hook? Belt hook was my original preferred option, well, actually, two- handed pull was my original thought but I'll have to remove a lot of material to get anywhere near that.

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