Designing a Slingshot Crossbow

Discussion in 'General Slingshot Discussions' started by Enn Block, Sep 3, 2012.

  1. Enn Block

    Enn Block New Member

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    So, when I started my introduction thread I asked which forum would be best to ask questions about making a slingshot crossbow, and I was told that the general forum was fine. If I made this topic in the wrong place, please move it. Because I have so many questions about designing a slingshot crossbow I decided to divide my questions into 2 topics: 1 on the physics/limits/potential of Theraband (mostly on theraband gold), and the other on designing a slingshot crossbow in terms of body design, materials to use, etc.<br><br>Questions on how to design a slingshot crossbow:<br><br>For his bands, Joerg says he likes the "clamp method", and has mentioned this both in a review of a slingshot and in the video showing his bullpup slingshot. I would like to make mine with a clamp as well. How would I go about doing this? (I do not have any tools to cut or shape metal) <br>1. Would the only requirement to be to attach a piece of wood or metal to the body of the crossbow and attach it with nuts and bolts to tighten/loosen it, or is there a specific way?<br><br>2. In my introduction topic someone mentioned using fairleads to tie string. Would they be useful for tying bands?<br><br>My next questions are about wood:<br>3. What sort of wood do you recommend for the body of a slingshot crossbow?<br><br>4. Joerg seems to use just normal wooden boards for his bullpup/blunderbuss slingshots, do these materials handle high band tension well?<br><br>5. Has anyone used a different kind of wood, like lumber (such as 2x4's) and is it any stronger than wooden boards?<br><br>6. If I end up using wooden boards/ 2x4 lumber to make the crossbow, would it be worth the effort to sand/stain/use some form of preserving coating on the wood, or is the material not worth the effort?<br><br>7. If so, what kind of coating should I put on it to preserve it? (I have looked at how to sand the wood on other topics so no need to repeat how to do it)<br><br>My next set of questions is about trigger design. I am planning to use the same trigger type as the one used for Joerg's blunderbuss slingshot, where the band pushes against the front of the release hook, causing it to lower and catch the band. You can see a picture of it on the first page of the blunderbuss topic several posts down. I wanted to ask:<br>8. The trigger seems to be cut from a wooden board and does not seem to be very thick. I am concerned about making a trigger of the same design, and so I am wondering, what is the best way to reinforce it so that the hook will not break under high tension?<br><br>9. The picture Joerg took of the trigger mechanism is too small for me to determine what he used for the axle on the trigger, what should I use?<br><br>Lastly I need to ask about the relationship between the bands and the body of the crossbow:<br>10. I plan to make the crossbow with pulleys to hold the slack band, (like on the bullpup crossbow and arm mounted crossbow), how wide should the bands be at most?<br><br>11. Should I use any sort of tapering on the bands?<br><br>12. How deep should I make the channel on the shaft of the crossbow? I know it is likely more specific to the size of the ammo I am shooting, so let us say theoretically I am shooting either balls with a diameter of 1/2 and inch or arrows/bolts with a shaft diameter of 1/2 an inch. How deep should the channel be for holding that kind of ammo?<br><br>13. Because the bands need to be able to pull the projectile across the shaft, they need to be close to the channel walls on the shaft. However, I do not want to have them drag against the shaft with every shot because I am concerned about adding wear on the edges of the band. could this issue be solved by making the pouch tall enough to fit inside the channel?<br><br>14. If I were to make the channel on the shaft wider than the projectile I normally plan to use will this adversely affect accuracy? Should the channel be designed to fit the normal sized projectile only?<br><br>15. If I were to cut the channel in the shaft such that instead of being rounded it has walls at a 45 degree angle and a flat bottom, would this be less accurate than a rounded channel?<br><br>If you have any ideas for how to make a trigger safety I would appreciate hearing about that as well.
     
  2. JoergS

    JoergS Administrator

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    Lots of questions! I am currently at a show and won't have full web access before Friday. Will answer over the weekend for sure.<br><br>
     

  3. Enn Block

    Enn Block New Member

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    I do not mind waiting one bit, especially because it means getting answers straight from the head honcho himself.
     
  4. JoergS

    JoergS Administrator

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    <table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>Enn Block wrote:</b></span></td></tr>
    <tr><td class="quote">
    <br>1. Would the only requirement to be to attach a piece of wood or metal to the body of the crossbow and attach it with nuts and bolts to tighten/loosen it, or is there a specific way?<br>
    </td></tr>
    </table>
    <span class="postbody"><br><br>You have to make sure the rubber is thick enough. The piece of wood (the clamp) will bend slightly. You can either put some extra rubber under and over the slingshot band, or leave it longer and fold it over. Thick bands (like three layers) need no such "upholstering". <br><br></span><table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>Quote:</b></span></td></tr>
    <tr><td class="quote">
    <br>2. In my introduction topic someone mentioned using fairleads to tie string. Would they be useful for tying bands?<br>
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    <span class="postbody"><br><br>I don't think so. But this may be a misunderstanding. <br><br></span><table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
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    <br>3. What sort of wood do you recommend for the body of a slingshot crossbow?<br>
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    <span class="postbody"><br><br>I use inexpensive wood, mostly spruce as this is what my hardware store sells. If you want beauty, lots of options. If I want delicate shapes, I use plywood because it is the most reliable type. <br><br></span><table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
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    <br>4. Joerg seems to use just normal wooden boards for his bullpup/blunderbuss slingshots, do these materials handle high band tension well?<br>
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    <span class="postbody"><br><br>If you make them thick enough, yes. Keep in mind the direction of the force is lengthwise, so there is little danger of splintering. <br><br></span><table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
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    <br>5. Has anyone used a different kind of wood, like lumber (such as 2x4's) and is it any stronger than wooden boards?<br>
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    <span class="postbody"><br><br>2x4s are mighty strong. But heavy and bulky.<br><br></span><table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
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    <tr><td class="quote"> <br>6. If I end up using wooden boards/ 2x4 lumber to make the crossbow, would it be worth the effort to sand/stain/use some form of preserving coating on the wood, or is the material not worth the effort?<br>
    </td></tr>
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    <span class="postbody"><br><br>If you want to shoot outdoors, I recommend oiling the wood so it isn't soaking up rain. Otherwise, you don't have to. <br><br></span><table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
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    <br>7. If so, what kind of coating should I put on it to preserve it? (I have looked at how to sand the wood on other topics so no need to repeat how to do it)<br>
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    <span class="postbody"><br><br>Linseed oil works best, just apply three coats or more with a brush. I use linseed oil from the supermarket. Of course you can also use commercial wood oil/stain for garden furniture and so on. <br><br></span><table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>Quote:</b></span></td></tr>
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    <br>My next set of questions is about trigger design. I am planning to use the same trigger type as the one used for Joerg's blunderbuss slingshot, where the band pushes against the front of the release hook, causing it to lower and catch the band. You can see a picture of it on the first page of the blunderbuss topic several posts down. I wanted to ask:<br>8. The trigger seems to be cut from a wooden board and does not seem to be very thick. I am concerned about making a trigger of the same design, and so I am wondering, what is the best way to reinforce it so that the hook will not break under high tension?<br>
    </td></tr>
    </table>
    <span class="postbody"><br><br>I use quality birch plywood for the trigger, the only wood material that is safe for such purposes. You can strengthen it with steel (which is what I do when the material gets too thin). I also use wood screws to hold the layers together. <br><br></span><table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>Quote:</b></span></td></tr>
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    <br>9. The picture Joerg took of the trigger mechanism is too small for me to determine what he used for the axle on the trigger, what should I use?<br>
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    <span class="postbody"><br><br>I use an 8mm aluminum tube, very smooth. Steel works, too, and is recommended for high draw weights. <br><br></span><table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>Quote:</b></span></td></tr>
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    <br>Lastly I need to ask about the relationship between the bands and the body of the crossbow:<br>10. I plan to make the crossbow with pulleys to hold the slack band, (like on the bullpup crossbow and arm mounted crossbow), how wide should the bands be at most?<br>
    </td></tr>
    </table>
    <span class="postbody"><br><br>Use my band calculator. For a crossbow, increase the values by 1.5 or 2. Don't make the bands too wide as they should stay on the rollers - wide rubber "wanders" off sometimes. <br><br></span><table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>Quote:</b></span></td></tr>
    <tr><td class="quote">
    <br>11. Should I use any sort of tapering on the bands?<br>
    </td></tr>
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    <span class="postbody"><br><br>Tapering increases the speed of the projectile and shortens the lifetime of the bands. Just find your personal preference. <br><br></span><table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>Quote:</b></span></td></tr>
    <tr><td class="quote">
    <br>12. How deep should I make the channel on the shaft of the crossbow? I know it is likely more specific to the size of the ammo I am shooting, so let us say theoretically I am shooting either balls with a diameter of 1/2 and inch or arrows/bolts with a shaft diameter of 1/2 an inch. How deep should the channel be for holding that kind of ammo?<br>
    </td></tr>
    </table>
    <span class="postbody"><br><br>The string that pushes the ammo needs to be in the middle of the projectile, or else it will slip under/over. Make the groove accordingly deep. <br><br></span><table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>Quote:</b></span></td></tr>
    <tr><td class="quote">
    <br>13. Because the bands need to be able to pull the projectile across the shaft, they need to be close to the channel walls on the shaft. However, I do not want to have them drag against the shaft with every shot because I am concerned about adding wear on the edges of the band. could this issue be solved by making the pouch tall enough to fit inside the channel?<br>
    </td></tr>
    </table>
    <span class="postbody"><br><br>I don't really understand the question. The bands should not touch anything really, as they will suffer greatly. Just make the string/pouch long enough so the bands run free.<br><br></span><table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>Quote:</b></span></td></tr>
    <tr><td class="quote"> <br>14. If I were to make the channel on the shaft wider than the projectile I normally plan to use will this adversely affect accuracy? Should the channel be designed to fit the normal sized projectile only?<br>
    </td></tr>
    </table>
    <span class="postbody"><br><br>By all means yes. a wider channel will allow the projectile to swing left and right in a chaotic way. <br><br></span><table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>Quote:</b></span></td></tr>
    <tr><td class="quote">
    <br>15. If I were to cut the channel in the shaft such that instead of being rounded it has walls at a 45 degree angle and a flat bottom, would this be less accurate than a rounded channel?<br>
    </td></tr>
    </table>
    <span class="postbody"><br><br>I often use 90 degree angles (just edges really). This reduces friction. You want as little friction as possible. <br><br></span><table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>Quote:</b></span></td></tr>
    <tr><td class="quote">
    <br>If you have any ideas for how to make a trigger safety I would appreciate hearing about that as well.</td></tr>
    </table>
    <span class="postbody"><br><br>I would recommend a lock safety rather than a trigger safety. Keep in mind the lock bears the entire draw weight. The design of a lock safety depends on the lock, really. Lots of methods.</span>
     
  5. Enn Block

    Enn Block New Member

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    Thank you Joerg! And don't worry about the question I didn't write all that clearly, because you gave me the answer I needed.