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    Edward donald
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    Post by Edward donald Fri Jul 26, 2019 12:03 pm

    Hi there

    I am new to posting in this forum but have used it in previous builds. I am looking to build crossbow prod useing  Yew and sinew only. Horn seems too time consuming. 

    I would like to follow a build I have seen by the user OrienM:

    https://thearbalistguild.forumotion.com/t1655-yew-and-sinew-prod-help-needed

    However i would like the draw weight to be at least 250lbs. I know this is a lot to ask without useing horn but is anyone able to give me a guess as to the dimensions for what that might be before tillering.

    On a side note the design of the crossbow is very unique as it allows the crossbow to cocked in under 3 seconds with a draw weight of 400lbs and utilises this speed of draw with a magazine of bolts. The materials used were available to anyone living in the period of when crossbows were still used on the battlefield and so from a historic sense this build is very interesting. The design is relatively compact and very easy to use with minimal effort in the loading process. 

    I'd very much appretiate any advice/help, and would be happy to reveal the design in a PM

    Regards

    Ed
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    Post by banuvatt Fri Jul 26, 2019 12:51 pm

    I am rather interested in your design, I found this on Youtube regarding the dimensions of your crossbow. But I'm not sure if you want to make a d belly shaped or flat bellyed prod. https://youtu.be/bvvsE2jtm9E
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    Post by banuvatt Fri Jul 26, 2019 1:04 pm

    But just as a reference or something to be off of maybe try 1.75" in width in the center tapering to 3/4". Try making a prototype at first so you have a good idea of how much wood to take off the prod. I've seen this skane crossbow that was made out of red oak it was 40" nock to nock, the width in the center was 1 1/2" for 4 inches on both sides. So it was full width in total for eight inches. Then it tapered to 3/4" wide tips at the nocks, for the center eight inches it was 3/4" thick and tapering down to 1/2" thick. The draw weight of the prod was 120 lbs. I hope this helps you in anyway.
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    Post by banuvatt Fri Jul 26, 2019 1:45 pm

    This maybe a bit experimental but why don't you try either reducing or taking off the sap wood if you can completely then putting the sinew on? You don't need sap wood on the prod if you have a backing such as sinew. It will make it so you don't have to remove as much wood as if you left the remaining sap wood on the prod. I think it will overall leave you will a crossbow that is higher in draw weight, but not as thick or wide if you chose to leave the sap wood on to get the same draw weight.
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    Post by Edward donald Fri Jul 26, 2019 2:06 pm

    Hi 

    Thanks for the reply

    The yew I am useing is italian yew and so the growth rings are very compact. I agree that taking the sap wood off would seem like a good idea as sinew essentially replaces it. however If i made the thickness 1.75 in the middle only 15-20% of that would be sap wood as it is so tight. I quite like the look of the sap wood as well but if you think its too much of a burden then maybe just leave it off. 

    Those thicknesses sound good to me. Havn't really found any guides on the internet for this yet.

    You say that the example you saw was 120lbs with a 1.5 inch centre. Do you not think 1.75 inches is not going to get you up to 300lbs?

    Yes, I will be making a prototype first. perhaps start with aiming for 250lbs

    very happy to show you the design.

    Send me a PM

    thanks
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    Post by banuvatt Fri Jul 26, 2019 2:23 pm

    Well I think if you added the sinew it would increase the draw weight. I think the sap wood is in my opinion just excess weight, if you already have a backing. This is just a guess, I could see your point about how 1.75" might not be enough I know of flat bows that have a width of 2-2.5" so you could try that.
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    Post by Geezer Sat Jul 27, 2019 7:56 am

    The sap wood is the springiest part of a yew bow.... don't remove it.  Just add sinew on top.
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    Post by stuckinthemud1 Sat Jul 27, 2019 12:11 pm

    The yew and sinew lath I have just finished is 110lb at 11" draw, it is 28" nock to nock, 1 3/4" wide at centre, the width is constant taper to the tips which are 1 1/4" wide, thickness taper is about 1/2mm per inch.  Thickness of lath at limb centre is in the region of 12mm, but the two limbs are different thickness due to one limb being stronger than the other so you would need to tiller your lath on a tillering bench to ensure an even bend (but you knew that).  Regarding sapwood, you have several options - don't bother with sinew - medieval wooden laths were not always sinewed; sinew over the sapwood and you don't need to use so much sinew as Geezer points out, the sapwood in yew does the exact same job; reduce the sapwood to nearly nothing as medieval longbow builders did and don't sinew; entirely remove the sapwood and replace with a good thick layer of sinew. All the options are valid and all have historic precedent.  Most modern bow builders would totally remove the sapwood if they were going to sinew as sinew can delaminate yew as it dries but I put a single course of sinew over my yew sapwood as I wanted to practice the technique and it held together just fine. 

    If you made the lath 30" long, nock-to-nock, 2" wide at centre and 15mm thick at the centre of each limb and used 3 courses of sinew, you would be close to 300lb at 8" draw length, I should imagine
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    Post by OrienM Sun Jul 28, 2019 10:31 am

    Not having worked with Yew wood, I don't have any intuition on ideal dimensions; my own wood/sinew prods were of Osage Orange, a much denser, stiffer wood. In my experience, a limiting factor is the force needed to steam-bend the stave into deflex; the thickest 40" long piece of yew you can still steam-bend might be a good place to start.

    I cringe to contradict Geezer, who knows more about crossbows than I'll ever know...however, personally I'd want to use all yew heartwood for a sinewed prod. My understanding is the heartwood is the more compression-strong component; the tension-strong sapwood isn't really needed under sinew, and I'd worry about adding weight and potential set by including it.
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    Post by Edward donald Sun Jul 28, 2019 10:37 am

    Thanks for that advice on the prod.


    I am going to get a feel for the dimensions by building a prototype out of a not such good bit of yew. without adding the sinew I will then tiller it until it breaks or reaches 220lbs. that hopefully will tell me how much roughly i'll need for the real thing.

     I will then proceed to the better wood and add the sinew. 


    Im in the workshop tomorrow so I'll keep you updated
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    Post by banuvatt Sun Jul 28, 2019 10:46 am

    What are you using as a wood glue? I heard of people using Titebond II or III as a glue for backing bows. Titebond III is water proof, while Titebond II is water resistant. Or are you using more traditional methods such as hide glue, or fish bladders?
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    Post by Edward donald Sun Jul 28, 2019 10:49 am

    hi i'm using hide glue

    Heard lots of bad things about modern glues. Something about how the molecular structure isn't given enough time to form with the quick drying process of modern glues. Not an expert at all so someone i'm sure can correct me.

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    Post by Edward donald Sun Jul 28, 2019 10:54 am

    banuvatt wrote:What are you using as a wood glue? I heard of people using Titebond II or III as a glue for backing bows. Titebond III is water proof, while Titebond II is water resistant. Or are you using more traditional methods such as hide glue, or fish bladders?


    hi i'm using hide glue

    Heard lots of bad things about modern glues. Something about how the molecular structure isn't given enough time to form with the quick drying process of modern glues. Not an expert at all so someone i'm sure can correct me.

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    Post by banuvatt Sun Jul 28, 2019 10:56 am

    If you watch Clay Hayes I think he uses Titebond III. He's a bowyer if you don't know him, go on to his Youtube channel. He has done tutorials on gluing sinew as a backing if I am not mistaken.
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    Post by OrienM Sun Jul 28, 2019 11:07 am

    DEFINITELY use hide glue...in my experience no other glue has quite the right qualities. Sinew and hide glue are basically the same material, collagen...they stick together extremely well, and shrink at a very similar rate. Titebond-type glues have been used successfully, but they won't shrink along with the sinew and add draw weight like hide glue does.

    Knox unflavored gelatin makes an easily available, inexpensive hide glue (I like 3 parts warm water, 1 part gelatin granules...briefly simmer, and use warm)

    It seems to work best to add sinew while the previous layer is still a bit damp; I usually apply sinew in a single, hours-long glue-up session, with only brief pauses to wait for the glue to jell up. Avoid touching the drying sinew with bare hands, since hand oils will impair the bond.
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    Post by Edward donald Sun Jul 28, 2019 12:23 pm

    stuckinthemud1 wrote:The yew and sinew lath I have just finished is 110lb at 11" draw, it is 28" nock to nock, 1 3/4" wide at centre, the width is constant taper to the tips which are 1 1/4" wide, thickness taper is about 1/2mm per inch.  Thickness of lath at limb centre is in the region of 12mm, but the two limbs are different thickness due to one limb being stronger than the other so you would need to tiller your lath on a tillering bench to ensure an even bend (but you knew that).  Regarding sapwood, you have several options - don't bother with sinew - medieval wooden laths were not always sinewed; sinew over the sapwood and you don't need to use so much sinew as Geezer points out, the sapwood in yew does the exact same job; reduce the sapwood to nearly nothing as medieval longbow builders did and don't sinew; entirely remove the sapwood and replace with a good thick layer of sinew. All the options are valid and all have historic precedent.  Most modern bow builders would totally remove the sapwood if they were going to sinew as sinew can delaminate yew as it dries but I put a single course of sinew over my yew sapwood as I wanted to practice the technique and it held together just fine. 

    If you made the lath 30" long, nock-to-nock, 2" wide at centre and 15mm thick at the centre of each limb and used 3 courses of sinew, you would be close to 300lb at 8" draw length, I should imagine
    Andrew


    Hi Andrew 


    Thanks for this. I will give these dimensions a go on a prototype

    However I would like the draw length a bit longer. If I increase the length of the prod to say 35" will that be ok to get a draw length of 11"?

    regards 

    Ed
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    Post by banuvatt Sun Jul 28, 2019 1:45 pm

    If you back it yeah it should be fine. You could go even shorter with a backing, the 1/3 rule I think really only applies to self bows. What I did with my prod is decided how much of the center would be full width. Then for the total length of the prod would be the center full width + the draw length times two.
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    Post by stuckinthemud1 Sun Jul 28, 2019 2:31 pm

    I did not steam any deflex unto my bow, just tillered very slowly and carefully. Bow took under 1/2 inch of set.
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    Post by stuckinthemud1 Sun Jul 28, 2019 2:36 pm

    My bow has a draw length of 11 inches and was tested beyond that. The bow needs enough draw length to get the sinew working and although it is mounted in a tiller drawing 8 inches, that is under stressing it and I am going to make a new tiller with the correct draw length one day. I would suggest 35inches is way too long, double draw length plus 10 per cent would be plenty, remember, power comes from width, flexibility from thickness. A wide, thin lath is very powerful and very bendy
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    Post by stuckinthemud1 Sun Jul 28, 2019 3:00 pm

    Oh One more thing, I appled my sinew using exactly the method Orion describes, go slow, keep calm and wait a couple of months for everything to dry fully
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    Post by banuvatt Sun Jul 28, 2019 4:47 pm

    I thought it took sinew backings to dry fully like six months to a year. This is according to what I had heard from bowyers who make Asiatic bows. Also I remember the topic of birch bark came up some time ago to protect sinew backings from moisture.
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    Post by Edward donald Sun Jul 28, 2019 5:48 pm

    stuckinthemud1 wrote:My bow has a draw length of 11 inches and was tested beyond that. The bow needs enough draw length to get the sinew working and although it is mounted in a tiller drawing 8 inches, that is under stressing it and I am going to make a new tiller with the correct draw length one day. I would suggest 35inches is way too long, double draw length plus 10 per cent would be plenty, remember, power comes from width, flexibility from thickness. A wide, thin lath is very powerful and very bendy

    I'd love to see this bow. is there a thread on this website?

    When you say that "double draw length plus 10 percent would be plenty" what exactly do you mean. 

    I would like a slightly longer draw length to show case the movement of the cocking mechanism. Obviously if this is going to mean breakage is more likely then i will stay at 8". Was just wondering what I might be able to do to get that longer draw. I am actually not that worried about power at the moment. Its all about showing that the cocking mechanism is able to draw back a very heavy bow to a long draw length.
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    Post by banuvatt Sun Jul 28, 2019 6:10 pm

    So if you times 8 with 2 you get 16, then you add 10% on a calculator for your final answer you get 17.6 inches long.
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    Post by banuvatt Sun Jul 28, 2019 6:16 pm

    Keep the center stiff and have only the limbs bend, as I mentioned before that 120 lb red oak board was 40" long ntn. The center was eight inches long, the draw length was 14 inches long. Since 40 - 8 = 32 you then get 16 when you divide that number by two.
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    Post by Edward donald Sun Jul 28, 2019 6:26 pm

    Oh i see you can work out the length ntn you need depending on what length of draw you want. So if I want 12"draw length i double: 24 +10% =26" . ntn

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