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    Recommendations for Pistol Crossbow

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    RevJ
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    Recommendations for Pistol Crossbow

    Post by RevJ on Sat Nov 24, 2012 3:28 pm

    New to crossbow building, know nothing about it, thought it would be interesting to give it a go ^.^

    I want to build a pair of pistol crossbows, but I want them to be powerful and at least decently accurate. I've read that, generally, pistol crossbows are neither. I have little to no idea what I'm doing, and some help would be nice Very Happy

    I've done a few calculations and determined that a prod with 120 lbs. draw strength exerts a tension force of 533.76 Newtons. I want my bows to each have a crank that automatically cocks the string after only one turn. At 533.76 Newtons of force, and with a draw length of one foot, and an average torque exerted by my arm of 220 Newtons (50 pounds), the ideal radius of the crank would be 29.1 inches. That ain't a very good radius. Obviously, this isn't really feasible, but with 7 turns (not TOO terrible), I could decrease the radius to ~4.2 inches. One of the problems I've run into is where exactly to stick the 8-inch crank on a hand crossbow that likely won't surpass 24 inches in length.

    Another issue is the material I should make it from. Carbon fiber is lightweight and more durable (I think, though I might be wrong) than wood. It's also pretty freakin' pricey. And difficult to work with. As an alternative to carbon fiber, what kind of wood, do you think, would be best to work with? I'd prefer a lightweight but strong wood that looks moderately presentable.

    What material should the prod be made from? I've read that spring steel can endure a lot of stress and is fairly cheap and available. Not quite sure what to use. I'd like a recurve prod that's strong (100+ lbs.), durable, and doesn't look awful.

    So these are the main problems I've run across thus far into the planning stage. I haven't educated myself fully about the mechanics portion yet, but I shall soon, and I don't foresee it being a large problem.

    Thanks for the help!
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    Re: Recommendations for Pistol Crossbow

    Post by B.Cheers on Sun Nov 25, 2012 1:47 am

    Well all i can say is just keep it simple it would be a lot easier to put a smaller prod on that you can pull back by hand then to try whack a crank system on i learnt that one the hard way.
    Also 24inchs is pretty damn long for a pistol crossbow my bullpup crossbow is only 9.8inchs long with out the stock, As for using spring steel for a prod it works wonders the one i made i was sure it was gonna snap yet its still holding up with no cracking or any sign of wear and tear.
    Thanks Ben
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    Re: Recommendations for Pistol Crossbow

    Post by kenh on Sun Nov 25, 2012 8:14 am

    Commercial crossbow pistols generally have a 17" or 18" prod, and the tillers are under 18" (and generally under 16") from bow to butt. You can buy 120# fiberglass replacement prods through Ebay for under $50. That length of prod I personally consider more of a carbine than a pistol, but that's neither here nor there..

    An 18" prod does not have anything like a 12" draw... more like 7"-9". And for 120# draw you really don't need the complications of crank cocking. A simple foot loop cord (which can double as a carry sling) will do the job perfectly well.

    Some of us are developing 'real' pistol-sized prods - 10" to 12" - with serious draw weights in the 50-100# class that will fit on real pistol-sized tillers under a foot in length.

    For the tiller there are any number of good 'exotic' hardwoods like Satinwood (which the Aussies call Silk Oak), Brazilian Walnut, and Zebrawood which are reasonably light and strong. Certainly not as heavy as Jatoba, Ipe, Ebony or Lignum Vitae. Look at a table of Janka Hardness values to get an idea of wood strengths compared to woods you may already know about like Oak, Maple, etc.

    Accuracy comes from many factors including the trigger mechanism, bolts used, track or bolt retaining system, shooter skill.

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    Re: Recommendations for Pistol Crossbow

    Post by RevJ on Sun Nov 25, 2012 9:14 am

    Yeah, I ended up reading further after posting and figuring out for myself the range of sizes for a pistol prod. Derp. I think I'm also just going to build a cocking lever onto the top of the crossbow - pull back, instant cock. But I do like the idea of a sling Very Happy

    As for accuracy: which kind of trigger is generally the most accurate? I was toying around with the idea of a bull-pup trigger, but I'm not sure if I want the bows to have stocks.

    Do you know if any smaller steel prods are commercially available? I'm not certain if I can get access to an angle grinder, lol

    Thanks,
    -R
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    Re: Recommendations for Pistol Crossbow

    Post by kenh on Sun Nov 25, 2012 2:55 pm

    Don't know of any smaller commercial prods available YET. As I say some of us are working on some things... You might try one of the 18" 50# fiberglass prods and trim 3" off each limb to see what you get.

    Checkout the crossbow Building Wiki and the threads here on various triggers/actions. Generally those with more than one pivot point will have a smoother action, which will certainly enhance accuracy.

    Bull pup setups are intended to reduce overall length. With a real pistol sized prod - say the size of a Gold Cup .45, you won't need that reduction as the action will already be sitting just above the trigger.

    I'm working up a 1" diameter roller nut style pistol sized action.

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    Re: Recommendations for Pistol Crossbow

    Post by RevJ on Sun Nov 25, 2012 4:04 pm

    Yeah, I'm not really certain if I want to use a fiberglass prod. I think I'm going to search around for a leaf spring and cut it down with my buddy's angle grinder to maybe 16" for a prod. Packs a bigger punch, if nothing else Razz

    I'll look around for a trigger design that's not too complex and will fit in a pistol crossbow.

    Thanks,
    -R
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    Re: Recommendations for Pistol Crossbow

    Post by Geezer on Sun Nov 25, 2012 7:16 pm

    Pistol crossbows: Surely I've said this before, but to reiterate... crossbow power is dependent on three factors: weight of draw, length of draw and prod efficiency. Pistol crossbows, due to their small size will be limited as to weight of draw and length of draw, leaving only one factor that can be manipulated in their favor.... efficiency. Steel prods are robust and nearly indestructible. They are not particularly efficient.
    Anybody who hopes to make an effective pistol crossbow will need to look at compound-pulley type systems using the most efficient prod-materials they can get. I would recommend starting with carbon-fiber composites.
    Beyond that, don't ask me, I'm sticking with medieval bows. Good luck stormin' da castle! Geezer.

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    Re: Recommendations for Pistol Crossbow

    Post by RevJ on Sun Nov 25, 2012 7:55 pm

    I'm not really skilled enough to build a compound bow :/ thanks for the tip, though!

    -R
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    Re: Recommendations for Pistol Crossbow

    Post by Geezer on Sun Nov 25, 2012 8:24 pm

    If you want a powerful, accurate pistol bow, the principles I outlined above are the ruling ones. A compound-bow would be potentially more powerful, though heavier and more complex. Longer draw-length and higher draw-weight will give you more power and accuracy. Lightweight, modern materials will give you greater spring for less weight, which equals improved efficiency. If you opt for reliable, easy to get steel, and go for light-weight and short draw, you may get a pistol-crossbow that's fun to shoot, but it won't be powerful and accurate.
    The situation reminds me of a sign we used to have in the print-shop where I worked years ago. "You want it, quick, good and cheap? Pick two and call us back." You want a strong, accurate, efficient, lightweight pistol crossbow? Pick two and call us back! From my experience, you aren't liable to get everything. Geezer.
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    Re: Recommendations for Pistol Crossbow

    Post by Todd the archer on Mon Nov 26, 2012 2:51 am

    I think your best bet for a powerfull pistol crossbow is to go with a reverse draw design. If you don't know what I mean, go to google images and type in "reverse draw crossbow".This gives you the longest power stroke but you have to go with a compound design.



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    Re: Recommendations for Pistol Crossbow

    Post by Geezer on Tue Nov 27, 2012 8:35 am

    So did you guys know Leonardo da Vinci has drawings of rudimentary pulley-bows in his notebooks. Since the pulleys available were fairly heavy, he mounted them to crossbow stocks, but the ideas are all there.
    Nothin' new under the sun. Geezer

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    Re: Recommendations for Pistol Crossbow

    Post by RevJ on Tue Nov 27, 2012 6:04 pm

    To be quite honest, I think I'm going to postpone making a pistol crossbow(s). I'd actually like to try making a full-size bow completely out of gaboon ebony. I love the color, and it's absurdly strong. Due to its high cost, I've been searching for the best possible deal. I've found one piece that's 24"x2"x2" and relatively cheap. I think I'll cut it down to 20x2x2 and use the remaining 4x2x2 piece as a handle that I'd attach to the stock. Would that be thick/long enough for a stock? I know ebony's very heavy and very difficult to work with; would making a stock entirely from ebony be feasible?
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    Re: Recommendations for Pistol Crossbow

    Post by Geezer on Tue Nov 27, 2012 6:37 pm

    You propose to make your crossbow stock from Gabon Ebony? Well perhaps you're a glutton for punishment, but in that case, why not bite the bullet and build it of ironwood or lignum vitae?
    I can only reiterate... go for a nice, stable fruit or nutwood, like cherry, beech, oak, maple, walnut? These are all proven woods, reasonable in price and reasonably easy to work. Bolivian or Indian Rosewood, ebony ironwood, lignum-vitae are expensive, very hard to work and often highly allergenic. But why listen to me? I've just been building crossbows for 30 years!
    Geezer, perplexed.

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    Re: Recommendations for Pistol Crossbow

    Post by RevJ on Tue Nov 27, 2012 6:45 pm

    I'm a masochist. And I really, really, really like the color and texture of gabon ebony. And the board only costs 30$ Razz

    I've always been pretty bad about jumping into a difficult project before finishing easier ones; stupid ADD. Lol.
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    Re: Recommendations for Pistol Crossbow

    Post by Geezer on Tue Nov 27, 2012 7:59 pm

    You're a masochist? 'Nuff said. Enjoy. DRW

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    Re: Recommendations for Pistol Crossbow

    Post by RevJ on Tue Nov 27, 2012 8:09 pm

    DRW?
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    Re: Recommendations for Pistol Crossbow

    Post by Geezer on Tue Nov 27, 2012 8:28 pm

    Yeah, DRW, my real-world initials. I sign all my business correspondence that way. This was a slip.
    And since we're back online, I figure a chronic failure to finish projects is often involved with subtle self-sabotage... Making the job really-really hard is a good excuse to give up on a challenging job. I had an apprentice who did that quite often. It took years to change that habit, but eventually she turned into a good crafts-person.
    That isn't to say YOU do this, but I've encountered it before.
    The doctor is now out... you owe me 50 cents for counsel. Geezer
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    Re: Recommendations for Pistol Crossbow

    Post by kenh on Tue Nov 27, 2012 8:29 pm

    DRW ...his real world initials.

    I agree with Geezer. Masochism is one thing; working with ebony is another! Wear goggles and a respirator, not just a paper mask, and be prepared to throw away your work clothes - the dust is really pervasive, not to mention moderately toxic!

    There are hundreds of other less expensive, beautiful fruit woods and exotics. $30 for a 2x2x24 stick is outrageously expensive. For a first try use something easier to work and the pocket book!

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    Re: Recommendations for Pistol Crossbow

    Post by RevJ on Tue Nov 27, 2012 8:40 pm

    @Geezer,
    I've had trouble with completing a project in the past, but not because of self sabotage Razz I tend to cycle a lot - I'm rather fickle regarding my interests. For the most part, though, I can power through just about anything if I'm motivated enough

    @Kenh,
    I like ebony Sad perhaps I'll buy the piece and postpone working it until a later date
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    Re: Recommendations for Pistol Crossbow

    Post by Geezer on Tue Nov 27, 2012 8:55 pm

    Sigh: Geezer
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    Re: Recommendations for Pistol Crossbow

    Post by B.Cheers on Tue Nov 27, 2012 9:09 pm

    @Revj i think your setting your self up for a hard crunch why not just build a simpler lower cost crossbow before rushing out and buying top dollar woods then at lest you can get the feel and a better understanding on what needs to be done.
    Thanks Ben

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    Re: Recommendations for Pistol Crossbow

    Post by chaz on Tue Nov 27, 2012 11:00 pm

    Revj,

    So far ...............just observing this bantering conversation, I'm lead to believe there is something more than simply being a masochist going on here, however, not being versed in the art of personalities, may I wish you the best in your quest. I'm sure we are all waiting anxiously for the posting of your results.

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    Re: Recommendations for Pistol Crossbow

    Post by Ivo on Wed Nov 28, 2012 11:17 pm

    Masochism?...dust in the nose?...sounds like a high-school girl's bathroom. Razz

    Prod.
    >>>Link

    It IS a steel prod, BUT it has a clever design ("v" shaped cross section) that makes it more stiff compared the limb with a flat profile of the same mass.

    Gnome did a build where he stacked these little prods to increase the draw weight you're also after in a pistol.

    http://thearbalistguild.forumotion.com/t618-crossbow-3-pistol-1

    Accuracy.

    Just as guys have said it...it's a combination and balance of a bunch of things...but hold on a sec...you're building a pistol bow, right? How accurately CAN one shoot off hand?

    Advice there is..

    Don't want a Full Stock? ~ do a Half Stock (like in the pic below...goes over the shoulder and you shoot it like a small bazooka tongue)...a little more control never hurt and technically it's still a pistol.



    On the side note...Pistols on their own, as I see them, are a recreational type of crossbow. Doesn't mean they can't be awesome and powerful, but for most part it's a back yard plinker for 20...maybe 30 yards.

    Trigger. (*bull-pup*)

    Chaz you pointed out that this bit needs to be added to the glossary...will do man, good looks.

    But yeah, *bull-pup trigger*...what the hell is a bull-pup trigger?...it's really *any* (literally) trigger with an extended trigger hook, done so via push or pull extension rod.

    If you look at the above picture, it's got just that - a set forward grip and the trigger extended following it.

    Wood.

    Just use morning wood... *hehe, now that's a masochist's masochist* Razz ...Just use what you got on hand...think of it this way - if you have patience to swing the file for hours non-stop and then sand it for hours more...then get the crazy hardwoods...if you're like me and can't stand it for more than an hour, get a softer hardwood. Maple is good choice (you can paint/stain it in sooo....sooooo many different ways). Stick to clean, simple lines - don't get too crazy.

    Signing off for now, but with the amount of attention you got, you better be thinking of a build-along topic right about now.

    Ivo




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