int(2) Trouble with my Gafa

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    Trouble with my Gafa

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    msalazar2310
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    Post by msalazar2310 on Mon May 21, 2018 1:21 pm

    Trouble with my Gafa Img_0211
    Trouble with my Gafa Img_0210
    By trying to span the bow, applying force with a long lever, two things happen:

    1.- The string goes far above the nut making impossible to cock it. Geezer suggested me to go  further back passing the nut and than slowly go back and the string goes down by itself. This I did it and finally the string was in place

    2.-The force I need to pull the string back is too much, (nothing to do with Tods videos where he pulls the Gafa lever with two fingers).

    My bow is 900mm. long, 40mm. wide in the middle, and 11mm. wide at the tips, the bow is made of automotive spring steel, with a thickness of 6.4 mm.6.4mm. 

    I would appreciate if you make me your recommendations for I am sure that I have done somethin wrong, possibly in the geometry of my gafa, or the bow with these meassures has got a draw weight far above to be cocked with it and I need a cranekin.

    Manuel Salazar
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    Post by Dark Factor on Tue May 22, 2018 12:05 pm

    What's the bow draw weight? I've never used this kind of lever but only the wooden one (from the stirrup) and with it we have about 2-3 times more force, not more.
    Force with 2 fingers doesn't mean a lot. I shoot 60lbs bows with 2-3 fingers. Stronger seems impossible for me but a friend of me can draw 130lbs bows with 2 fingers too and it doesn't seem hard for him !
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    Post by msalazar2310 on Tue May 22, 2018 6:27 pm

    I do not know thw draw wight, I assume it may be 200 pound
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    Post by msalazar2310 on Wed May 23, 2018 2:07 pm

    https://youtu.be/iIkxyjVu9gc

    This is what I mean by "holding the lever with two fingers"
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    Post by c sitas on Wed May 23, 2018 4:07 pm

    yes ,that is all well and good. Notice where the fingers of the lever set when starting out. He has lots  of leverage this way. The way your's are setting ,you have no leverage at all. Fingers are too long.
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    Post by msalazar2310 on Thu May 24, 2018 8:47 am

    Thanks a lot, I made the fingers longer as necessary in order to have "room" for corrections, one ting I also can do is to relocate the pin, however I will have to guess in what direction, this prior to modify the curve of the fingers, whtever ideas you got, let me know
    Manuel
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    Post by Dark Factor on Thu May 24, 2018 10:18 am

    Not sure the length of the 2 fingers of the lever are a problem. If it's longer than necessary, there is no problem.
    But is it the final lever or an old picture ? I mean there is no lever limb. For me, the length of the limb is the force multiplier... the longer the better for multiplying the force.
    That's only physics... if the final distance between the nut and the lever axis is 4 times smaller than the distance between your hand and this axis, you multiply force by 4... if more, this will be easier
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    Post by Geezer on Thu May 24, 2018 12:31 pm

    Certainly the lever in the photo has no upper limb.  That's what gives you the 'leverage'.  Also note that the 'fingers' on the illustrated lever are mounted on a thru-axle (Yes, Payne Gallwey's pattern does it that way) but in fact plenty of 'gafa' or 'goatsfoot' levers hang the fingers on two rivers, with no axle.  The advantage to doing it that way is that the axle doesn't limit the range of motion on your lever.  I have seen a few period bows with marks on the stock where the axle for fingers would end up stricking the top, but I've also seen lots of these bows (Padre Island bow or Maltese bows) with no such marks. 
    In some cases, the missing upper limb is immovable, but most of them swivel, so the lever can be folded when not in use.  Geezer.
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    Post by drawknife on Fri Jun 15, 2018 2:56 am

    Hi,
    Just to add what has been said;
    The shape of the bent levers near the claws is not the correct shape, See Payne Galways goatsfoot lever design. (should be on the internet).
    Your device needs an extended lever forward of the  bars that you use to pull the device back. this will give you more leverage.
    The smoother you can polish the sliding surfaces the easier it will be to pull.
    I made one of these to (almost) Payne-Galways design and it worked but still lifted the string. It is all in the shape of the curved legs.
    Hope this helps

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