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    Hello from the north

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    a_macdiarmid
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    Hello from the north

    Post by a_macdiarmid on Sun Jan 27, 2013 6:33 pm

    Hello Guild,

    Let me start by saying to my embarrassment, that after having signed up some 2 years ago the thought had only come to me recently that it might very well be high-time I actually committed to any communicative activity on the forum. Which is a fantastic resource by-the-bye. A thanks to the community.

    Not much to say I suppose , other than my arbalest bend is mostly looked on by complete confusion by anyone and everyone around me or even by myself really for that matter, not that I mind however. I have built one bow so far which was made in a ridiculous hurry, but thankfully have plans to build a few more... insh'allah. Oh that little mangled bit behind the nut was my lesson in not trying to stop the nut from spinning. Not sure why I even wanted to do that in the first place. Smile



    All the best,
    Alan

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    Re: Hello from the north

    Post by Geezer on Sun Jan 27, 2013 6:54 pm

    Yup, a spinning nut... particularly a metal nut on a strong bow, has lots of inertia. Stopping it can be tricky... and damaging. Been there, tried that. Nowadays, I just let 'em spin till they stop.
    Geezer.

    mac
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    Re: Hello from the north

    Post by mac on Sun Jan 27, 2013 8:32 pm

    The "mangled bit behind the nut" must have been cropped out of the pic.

    I've trained my self shoot with my thumb right on the nut. This keeps the bolt in place, and leaves my thumb in a good position to stop the nut. The faster you stop the nut, the sooner you can reset it and let go of the tickler.

    Mac

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    Re: Hello from the north

    Post by Geezer on Sun Jan 27, 2013 8:38 pm

    Yep, unlike we modern shooters, who hold against the shoulder, most period illustrations show the fore-hand underneath the lock, presumably with a finger atop the nut... that would obviate necessity for a bolt-clip and speed resetting the lock. Yer doing it right, Mac... as usual, darnit! Geezer.

    shiloh
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    Re: Hello from the north

    Post by shiloh on Thu Jan 31, 2013 5:18 am

    Hi Alan, nice bow, good to see a fellow Canuk in the same area. Yea the folks around me don`t get the desire to build bows either, they figure the time would be better spent just buying off the self. To that I say nope!
    I`d rather be out in the shop.

    Cheers

    jds6
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    Re: Hello from the north

    Post by jds6 on Thu Jan 31, 2013 10:02 am

    Greetings;

    Nice bow indeed!
    As far as people not understanding your passion in crossbows, well, I guess we all have been there are still are. After a year and a half of crossbow building people still think I'm a little off!
    My wife would say" crossbow this crossbow that!" Now she wants me to build the next one for her!
    Thanks for sharing your project, and happy building!

    jds6

    a_macdiarmid
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    I'm new to crossbows


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    Re: Hello from the north

    Post by a_macdiarmid on Fri Feb 01, 2013 11:43 am

    thanks for the welcome guys. I've started my new project. slow as ever.

    Can I ask if anyone has had any necks break from too strong a prod/to thin a design etc... purely conjecture I know as every variable makes a difference. but just trying to assess whether if it looks reasonable its likely to be reasonable, or if theres more to know.


    mac
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    Re: Hello from the north

    Post by mac on Fri Feb 01, 2013 1:43 pm

    A_MacD,

    I am glad to see you address this. The wood between the prod and the nut is loaded primarily in compression. There is a small bending load, but it is hardly worth talking about. I have never seen a tiller even flex here, let alone break.

    Most modern makers err on the side of too much wood in their tillers. Our ancestors were content to use much lighter tillers to support much stronger prods. I recommend to everyone that we all take a good hard look at the proportions of authentic old crossbow tillers, and than vow to never make one that is the slightest bit thicker.

    (I shall now climb down from my soap box)

    Mac

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    Re: Hello from the north

    Post by mac on Fri Feb 01, 2013 1:51 pm

    ....There is a pic of one of my bows on the second page of this thread. http://thearbalistguild.forumotion.com/t223p15-wood-prods-general-question

    I have made it pretty slim, and there is no sign of any trouble.

    Mac

    jds6
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    Re: Hello from the north

    Post by jds6 on Fri Feb 01, 2013 2:45 pm

    Mac,
    Since you are the topic of tillers, what was the average width of the one's our ancestors use?

    jds6

    mac
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    Re: Hello from the north

    Post by mac on Fri Feb 01, 2013 3:25 pm

    JDS,

    I'm afraid I don't have any numbers.

    Whenever I build anything, I draw it out in at least two views at full scale, working within any known dimensions or parameters. For example, if I know the overall length of the tiller, or the diameter or width of the nut, I make the other dimensions "work" within that. Once the project has a physical, three dimensional existence, I can view it from the same angle as my pic of the real one, and ask myself "where does this look wrong" and then correct it.

    I sorry to get all theoretical on you when you just wanted numbers, but that's just how I work.

    If you show me a picture of a crossbow with one known-dimension, I'll bet I could figure out the dimensions of the tiller within a couple of percent. (This could be a sort of crossbow geek's party game!)

    Mac

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    Re: Hello from the north

    Post by mac on Fri Feb 01, 2013 3:44 pm

    a_macdiarmid wrote:

    Looking at this bow here.....

    I would guess that the nut is about 1" wide, and maybe 1 1/8" in diameter. I put the bow at about 2 1/4" tall in the center, and the distance from the back of the bow to the axis of the nut at 7 1/2". If all that's the case, the width of the tiller at the "nut well" is about 1 1/2". The height of the tiller at the nut well is no more than 1 3/8". The narrow part of the tiller, between the bow socket and the nut well is probably about 1 1/4" tall and perhaps no more than 1" wide. The width at the bow socket is probably about 1", or maybe as narrow as 7/8".

    This is a fun game!

    Mac

    jds6
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    Re: Hello from the north

    Post by jds6 on Fri Feb 01, 2013 4:57 pm

    Mac,
    That's a great gift you have there! Hopefully some day I can pick up on things like that.
    I knew the tiller was thin but didn't realize that slim. Personally I like the slim line tillers myself.

    Thanks Mac for all the info !
    SLIM and TRIM!!!!!

    jds6

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    Re: Hello from the north

    Post by Geezer on Fri Feb 01, 2013 5:32 pm

    Mac's figures for that skinny Germanic bow look about right, and in fact, the Padre Island bow is built to similar dimensions. It's about an inch and three-eighths wide and high at the lock. Roller is 1 inch wide and very slightly more in diameter (1&1/6 TO 1&1/8 dia.) At the tail, the stock may be 1 inch square, but possibly narrower. There are lots of high-middle-ages bows that are really-really skinny. It's the later 15th and 16th century bows that are chunky through the lock and head, but still the hefty Flemish arbalests are only about 1&5/8 wide. My customers tend to buy thicker stocks, so I make a lot of those, but in fact, you should be able to build substantially strong bows with very light stocks. Some sources suggest the Weight of the prod should no more than the Weight of the stock, or you'll have too much recoil! Geezer

    mac
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    Re: Hello from the north

    Post by mac on Fri Feb 01, 2013 8:42 pm

    As far as I can tell, there are three things that make the later crossbows have heavier tillers.

    The first is stronger bows, including steel ones. These just plain put heavier loads on the fore part of the tiller, and it has to be thicker to stand up.

    The second is the use of spanning mechanism that anchor behind the nut. With a stirrup and a belt hook, the nut-well area never sees any of the spanning load. By contrast, a hook and pulley or hook and roller subjects the nut-well to a force of about 1/2 the draw weight of the bow. Consequently, these tillers must be more robust through that area.

    With cranequins, the nut-well must resist the entire draw weight, and these tillers must be beefier yet. The nut-well area of these tillers is typically wide and bulgy as well as deep.

    (A crossbow that is spanned with a goats-foot leaver has the same sort of stress issues, but here the nut-well ares is typically reenforced with metal plates. This is more suitable to the geometry of the goats-foot than the bulgy nut-well areas of cranequin bows.)

    The third is the development of a more ergonomic cheek. This makes the back end of the tiller taller to accommodate the asymmetric flat area that allows the shooter to get his eye centered over the tiller without tilting his head.

    Mac

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    Re: Hello from the north

    Post by Geezer on Fri Feb 01, 2013 10:20 pm

    Yup, in a nutshell. Geezer

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