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    Finnish crossbow project

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    Juri
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    Finnish crossbow project

    Post by Juri on Thu Feb 05, 2015 7:30 am

    Hello guys!
    I am Juri, from Finland. I have been lurking here for a while but now is the time to start a project of my own.
    Me and my colleague, Jari, managed to get two pretapered spring steel billets from master smith Taisto Kuortti. We decided to try two traditional Finnish crossbows. We have never made steel prods or crossbows before. So, we probably will need your generous help in various stages...
    Here is some dravings about the model, made by etnologist U.T. Sirelius 1919.
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    Juri
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    Re: Finnish crossbow project

    Post by Juri on Thu Feb 05, 2015 7:50 am

    Here is where we started. 860 x 50 mm, about 34 x 2 inches. Imatra MS 416 spring steel.
    Tapering from 8mm, 0,3" from center to 4mm, 0,15" at the tips.




    Cut in shape. 45 mm, 1,77" at the center, 27 mm, 1,06" at the tips.



    Then "a bit" grinding to make the both limbs as symmetrical as possible.



    to be continued...
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    Juri
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    Re: Finnish crossbow project

    Post by Juri on Thu Feb 05, 2015 7:54 am

    Shaping the tips. That's Jari.



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    Juri
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    Re: Finnish crossbow project

    Post by Juri on Thu Feb 05, 2015 8:00 am

    Nocks welded from 12 mm, 0,5" bolts.







    And the final shape.

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    Juri
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    Re: Finnish crossbow project

    Post by Juri on Thu Feb 05, 2015 8:37 am

    Ok, shaping the side profile.
    We also used a template made of thin metal plate to get the shape right and symmetric.



    Me inspecting quality.



    After steel brushing.

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    mac
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    Re: Finnish crossbow project

    Post by mac on Thu Feb 05, 2015 9:32 am

    Juri,

    The bow's widths and thicknesses look good to me, but I am worried about the amount of recurve at the tips.  Check it against the bow in the first pic you posted and I think you will agree.  As it is, the string will rest on the bellies of the limbs when it brace height.  In my experience that will make the string tend to come off at the end of the shot.  That's bad for the bow as well as your peace of mind Shocked

    This should be easy to change if you have not hardened it yet.

    Mac
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    Re: Finnish crossbow project

    Post by Geezer on Thu Feb 05, 2015 10:39 am

    Thanks guys for posting the stuff about Finnish crossbows. It allowed me to chase down Sirelius' 1919 drawings online.  I've had lousy photocopies of those bows for years... faint and small sized.  Now I've got fresh new ones that can be blown up to any size I want.  Geezer
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    Re: Finnish crossbow project

    Post by Juri on Thu Feb 05, 2015 11:25 am

    Thank's for the replys!
    Mac, unfortunately It is allready hardened. I have also started to doubt there might be too much reflex.
    If the string jumps off, then the prod must be shaped and hardened again. We will see...

    Well, here is the hardening process.
    That was made by a professional smith Jarkko Kotakorpi, company called Vallilan Takomo. They are making leaf springs for vehicles there.



    For a case that the prods twist in hardening I welded them together. The smith also added a clamp in the middle.



    Here it goes! First to owen 940° C, 1724° F and then to water.
    This stage can be a step forward or a looong jump backwards, if something goes wrong.



    I tried to film everything, but I was so nervous that I pushed a wrong button in my camera.
    However, it went well! Here is my relieved face with the prods, hard as a glass.



    After this the prods went for annealing 430° C, 806° F for 2 hours. That owen is just behind my back.
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    Juri
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    Re: Finnish crossbow project

    Post by Juri on Thu Feb 05, 2015 11:37 am

    Well, this is the situation today.
    Not a glue about the brace height, draw lenght or draw weight yet.
    First experiment with a long string, I'm trying to figure out how long and how thick should the real string be. I'm planning to use B-50 Dacrong at first.
    The tips have moved 5 cm, 2" and the weight is allready 190 pounds. Looks like I need a bigger scale!

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    Re: Finnish crossbow project

    Post by ali.j on Thu Feb 05, 2015 3:29 pm

    nice. Shocked

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    Re: Finnish crossbow project

    Post by Hermit on Thu Feb 05, 2015 5:29 pm

    Juri,look at my posting today 'R.D.T' experiments.The posting has a method I have used to determine the number of stands needed for any given draw weight,this will give you an idea of string thickness.It worked for me,hope it works for you.
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    Re: Finnish crossbow project

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