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    New modern crossbow build - trigger/lock choices?

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    kiltedcelt
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    New modern crossbow build - trigger/lock choices?

    Post by kiltedcelt on Wed Jan 22, 2014 10:31 pm

    While I'm working on a 1500s German hunting crossbow I have a mind to build a totally modern hunting crossbow. My first thought is to build it using a roller nut and a trigger mechanism that would be a little bit easier and less cumbersome to actuate than the traditional tickler. The bow I want to build will have a traditional rifle like stock and possibly a mount for a scope or other type of sight. My main question is, what would be the advantage of a lock like a clap lock over a roller nut type of release? Also, the prod I'll be using will have a minimum draw weight of 125 lb so the tension on the string shouldn't be excessively high. With a normal rifle style of stock can a shorter rifle type of trigger actuate a clap lock or roller nut type of mechanism?
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    Re: New modern crossbow build - trigger/lock choices?

    Post by Todd the archer on Thu Jan 23, 2014 2:06 am

    Can not say for sure what advantages a clap lock has but I like it. Here is my build:

    http://thearbalistguild.forumotion.com/t422-starting-a-new-project

    If you don't go the double trigger route I am pretty sure a regular trigger will work as well.

    If you have questions I will try to answer the best I can.

    Todd

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    Re: New modern crossbow build - trigger/lock choices?

    Post by Rizzar on Fri Jan 24, 2014 12:24 pm

    Advantages of a claplock (not to confuse with a clawlock) are force distribution to the tiller so the lock only has to hold a small part of the draw weight and there is no or little energy used to open the lock in comparison to the rotation energy required for a more or less heavy roller nut.

    This generally improves mechanism speed leading to better shot behavior/accuracy.

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    Re: New modern crossbow build - trigger/lock choices?

    Post by kiltedcelt on Fri Jan 24, 2014 6:09 pm

    As this will be a bow used for hunting, there is some weight that can be given to using a claplock mechanism because the spinning roller nut can be a potential issue with spooking the animal that has just been fired at apparently. Since this bow will utilize a modern rifle-like stock, I'd prefer not to have to use a lengthy lever to engage the lock, be it a claplock or roller nut mechanism. In either of those instances, the lengthy lever would look out of place on the modern type of stock.

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    Re: New modern crossbow build - trigger/lock choices?

    Post by Rizzar on Fri Jan 24, 2014 11:57 pm

    Depends what would be a lengthy lever to you...

    And of course depends on designated draw weight. What do you consider to be sufficient for your hunting tasks?
    With "normal" crossbows you usually can cock the weapon either by hand or easiest way a rope spanner or worst case a spanning belt.
    But if you aim higher perhaps a lever will be needed or just better.

    Regarding to the spinning nut, do not think the animal will be spooked by the rotating nut, more likely it will be spooked by a relative loud crack the crossbow will make when shot.
    And if built without guiding axle the nut usually will not rotate a very long time.

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    Re: New modern crossbow build - trigger/lock choices?

    Post by kiltedcelt on Sat Jan 25, 2014 5:58 am

    Rizzar,
    Most areas seem to require a minimum hunting weight for a crossbow to be at least 125lb draw weight. I'd like the option of taking larger game than deer at some point so I was looking at a prod that would give a draw weight between 150 and 200lb. As far as the long lever goes, the whole point of making a rifle-like stock is to get the trigger mechanism farther forward and closer to the lock. To get the leverage to disengage a lock on a crossbow with a long lever it seems like the shooter is usually having to pull on the lever at the end farthest from the lock. I'd actually prefer to have the trigger mechanism be as close to a normal rifle as possible, with a small gun/rifle-like trigger fairly close to the lock.

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    Re: New modern crossbow build - trigger/lock choices?

    Post by Rizzar on Sat Jan 25, 2014 6:14 am

    Ahh, you mean the trigger lever.

    I always thought about a spanning lever...


    There are various designs of trigger systems that benefit form different lever situations.
    Some are closer to the lock, some more to the "butt" end.

    Usually with single axle mechs you need a longer lever to pull the force, especially with high loads (btw I for myself consider 150-200lbs to be a lightweight crossbow though enough power to kill depending on distance and bolt mass).

    When thinking about your stock design remember everything has to fit to the prod. The prod is the most crucial part and getting the maximum out of a prod is paramount for speed and further impact energy.
    Prod first...

    A multi axle trigger can be designed to have a rather short distance to the lock but still be able to hold several hundrets of pounds.
    Claplocks can be easily built to work with short distances, too.

    Triggers can be made in many ways, I´d suggest you to have a look at the youtube channel of a friend. You can see some historical examples of triggers that can be modified by inner lever length. Here as an example for the Claplock with short inner lever:
    http://www.youtube.com/watch?v=qUCEFqof25Q
    (concerning your designated poundage I´d bet the inner lever can be designed even shorter with some disadvantage of trigger resistance)


    Rizzar


    Last edited by Rizzar on Sat Jan 25, 2014 6:21 am; edited 1 time in total (Reason for editing : grammar spelling ...)
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    Re: New modern crossbow build - trigger/lock choices?

    Post by Todd the archer on Sat Jan 25, 2014 6:30 am

    In case you did not see this in my thread here is a pic of my claplock mechcanism. As you can see it is quite compact.





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    Re: New modern crossbow build - trigger/lock choices?

    Post by Rizzar on Sat Jan 25, 2014 7:38 am

    Yeah, that is a great example of using a pivot point to compress mechanism length.
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    Re: New modern crossbow build - trigger/lock choices?

    Post by kiltedcelt on Mon Jan 27, 2014 1:53 pm

    I didn't want to go with anything too complicated - ie. not too many pivots or extra parts. I realize that fewer pivots/less axles will increase the force required to release the trigger/lock. I talked at length with the owner of SloBows regarding prods, and trigger mechanisms. On his advice I'll be building this bow with a roller nut lock instead of a clap lock. He had some examples of simple designs of trigger mechanisms for a roller nut lock that only utilize a couple axles and still have a light trigger. He said he'd email me some diagrams or photos of what he's talking about. I have the book, Crossbows in the Royal Netherlands Army Museum, and in there on page 38 there is a simple two axle design for a roller nut for a target crossbow that I think I'll follow for my design. The only thing I don't like about this otherwise simple design is the need for a pin that pushes through the top of the stock to reset the trigger. I'd prefer to have the trigger reset itself by the act of bringing the string back into the roller nut. I'll be interested to see what sort of diagrams or photos I get from SloBows. I've pored over the trigger mechs thread but alas, find it almost useless because it's concerned mainly with clap lock type mechanisms and adapting actual rifle type triggers to crossbow applications. What  I want with this bow is a stock that looks fairly modern in design with some slightly "archaic" touches, what with the roller nut and a simple lock design.
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    Re: New modern crossbow build - trigger/lock choices?

    Post by Todd the archer on Tue Jan 28, 2014 2:47 am

    It is not necessary to make the caplock complicated and I am sure it is possible to make a two axle version with a light trigger pull with out going to a long trigger lever. So don't rule them out thinking they need multiple axles to work well.

    Interested to watch your progress so keep us up to date.

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    Re: New modern crossbow build - trigger/lock choices?

    Post by kiltedcelt on Tue Jan 28, 2014 10:43 am

    Todd,

    I'm still in the planning stages - "doin' a bit of ciphering" as a master carpenter I used to know would say. I'm going to head out today to pick up some rigid foam insulation for roughing out stock mock-ups before I tackle a nice piece of hardwood. I'm starting to zero in on what sort of layout I'm wanting for the stock, taking into account the prod draw length, type of axle/lock and some of the other considerations I mentioned such as a longer table to support the longer arrows. I predict it's going to be an interesting looking beast. I also plan to have a lot of etching on the various metal parts - everything from the prod to the lock plates, as well as some decorative carving on the stock as well.

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