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

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» 12th Century Chinese Crossbow Chronographed
by stuckinthemud1 Fri Nov 24, 2023 3:50 pm

» Crossbow Stock
by kenh Tue Oct 31, 2023 6:19 am

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» flexible string
by jasper1978 Mon Mar 20, 2023 1:25 am

» [solved]Skane/Lillohus crossbow thread
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» jens sensfelder
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» Digitar prodsc
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» Troubleshooting
by Andy. Fri Jan 06, 2023 12:29 pm

» Wood Prods
by stuckinthemud1 Fri Dec 30, 2022 12:47 pm

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» Fiberglass H-bows
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» Anyone make their own bolts?
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4 posters

    Skew of tiller

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    crusader
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    Skew of tiller Empty Skew of tiller

    Post by crusader Sat Aug 07, 2021 3:07 am

    Dear members,

     
    I want to determine the skew of stock.  
    on the front side.  
    where should the string touch the stock?  
    when he's behind the rollernut?  or at the BH height?  

    I would like to hear from you.

    Regards,

    Crusader
    kenh
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    Skew of tiller Empty Re: Skew of tiller

    Post by kenh Sat Aug 07, 2021 8:34 pm

    The string should touch the prod at brace not at cock.
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    Skew of tiller Empty Re: Skew of tiller

    Post by crusader Sun Aug 08, 2021 8:02 pm

    Heej Kenh,


    prod must be stock I think?  
    I just thought it was the other way around.  
    why are the sides always chamfered? 
    along the draw length?

    Regards,
    kenh
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    Skew of tiller Empty Re: Skew of tiller

    Post by kenh Mon Aug 09, 2021 4:06 pm

    Yes -- prod in tiller.  Prod angled down so that string at brace is touching the bolt track.

    Sides are "rounded" along the draw length of the tiller because when the string is in the cocked position it is pushed downward onto the tiller and sharp edges cause unnecessary string wear.
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    Skew of tiller Empty Re: Skew of tiller

    Post by crusader Tue Aug 10, 2021 8:34 am

    hey,

    Thanks for your reply.

    I thought if the string touches the tiller at BH,

    If you then bring the string back in a squard line with the prod, there is space created between the string and the tiller.

    So I thought wrong.

    Best regards
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    Skew of tiller Empty Re: Skew of tiller

    Post by crusader Thu Aug 12, 2021 6:17 am

    Skew of tiller Tough_10
    Skew of tiller Tough_11
    Here's a drawing of what I mean.

    What will be most efficient?

    maybe the string/tiller intersection in the middle of the draw length??

    I get to 15 degrees at the BH.

    and 7.5 degrees behind the roller nut.

    I think it's worth discussing again.. Smile

    let me know!
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    Skew of tiller Empty Re: Skew of tiller

    Post by kenh Thu Aug 12, 2021 1:27 pm

    See the dot in the top sketch where you have 88.9??  Remember that your prod is curved when strung, and that dot would be about where the string should be, sitting on the surface, when the prod is at rest. Not where you show it aft of the 9.  If I remember correctly the angle is 12 degrees.

    If you set it up as in the second drawing, the string is going to scrape down the entire deck to the prod, wasting its energy and significantly reducing the energy transferred to the bolt.  Not to mention causing massive wear and tear on the string itself...
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    Skew of tiller Empty Re: Skew of tiller

    Post by crusader Fri Aug 13, 2021 3:54 am

    Skew of tiller 1751_d13
    Okay,

    Here the design; what do you think?

    I think the degrees is too much. it is now 17.51 ​​degrees!

    so the bow doesn't hit the tiller BH

    There is now 10mm above the prod and tiller.

    As the distance increases, the degrees also increase.

    how many mm do you always wear for that?
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    Skew of tiller Empty Re: Skew of tiller

    Post by stuckinthemud1 Sat Aug 14, 2021 1:04 am

    Don't forget string is flexible, it moves up and down and you lift and drop it as it goes over and behind the nut

    Up to a point, you need the string to slide along the deck as it needs to collect the bolt, not hop over it  this is where 'art' comes into things. Also, as the string pushes down on the table at BH, it acts as a brake helping stop the prod over extending. I think you have to accept a level of trial and error, my current project is too tight to the bolt table and is going to need adjusting, its a nuisance but only an afternoon's work to do, so not the end of the world.
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    Skew of tiller Empty Re: Skew of tiller

    Post by crusader Sun Aug 15, 2021 3:16 am

    hey,

    I'm going to make a test model in pine wood.

    and see how everything behaves.

    if all goes well I will make it from a more expensive type of wood.

    Thanks for the responses.
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    Skew of tiller Empty Re: Skew of tiller

    Post by crusader Sun Aug 15, 2021 3:19 am

    here are some more pictures of the slants in different designs and versions.

    As you can see there is a lot of difference between them.

    Skew of tiller Barbar10
    Skew of tiller Dan_sn10
    Skew of tiller Lindyb10
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    Skew of tiller Empty Re: Skew of tiller

    Post by crusader Sun Aug 15, 2021 3:20 am

    Skew of tiller Lindyb11
    Skew of tiller Pinter10
    Skew of tiller Rus10
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    Skew of tiller Empty Re: Skew of tiller

    Post by crusader Sun Aug 15, 2021 3:20 am

    Skew of tiller Todstu10
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    Skew of tiller Empty Re: Skew of tiller

    Post by drawknife Fri Aug 27, 2021 9:18 am

    First of all let us start with a few basics. A crossbow prod is not symmetrical when viewed from the front. Its top edge curves upwards from its middle and the string notches are level with or above the top surface when not braced. The angle needed to fit the prod to the tiller/stock is determined by bracing the prod and finding the angle the prod makes with the front of the stock when the string is just touching the top surface. as the string is drawn back towards the nut the string notches not only pull backwards but also curve downwards allowing the string to remain just touching the stock. (Try this by doing a V sign with the fingers of your left hand and holding your palm at a slight angle to horizontal. Pull your finger tips back with 2 fingers from your other hand. As your finger tips come back they also drop lower towards your palm). this is what should happen with the string notches on your prod which allows the string to glide without friction across the top of your stock. 
    The medieval crossbow designers were a clever bunch.
    ps It is not easy to explain what happens without a video but you could try it with a wooden model using a thin bendy strip. A shallow u shape should do the trick.

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    Skew of tiller Empty Re: Skew of tiller

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