Jan 8, 2016 | By Alec
There’s no discussion in the 3d printing community that is more divisive than 3D printed guns, but other 3D printed weaponry is usually far less controversial. Perhaps because they’re often far cooler and less lethal? Nonetheless I won’t want to be on the other side of this 3D printed crossbow by DIY Dudes either. While some 3D printed mini crossbows have circulated the web before, DIY Dudes’ Dan has just completed a this very impressive, full size and largely 3D printed medieval weapon that packs a serious punch, as you can see in the clip below.
DIY Dudes, in case you’ve never heard of them, is an interesting blog full of cool 3D printed designs, with an impressive bow among them as well. Perhaps that partly inspired Dan to move on to the most lethal weapon of the Middle Ages, which was famous for being powerful enough to pierce a knight’s complete armor from a far distance. As he explains on his blog, this project was also partly inspired by the limitations often attributed to 3D printing: that 3D printed parts are supposedly very limited and strength and require careful design to make anything capable of withstanding pressure. "With this in mind, I pose the question: is it possible to 3D print a powerful full sized crossbow? Yes, in fact, it is,” Dan says.
The design he came up with is very impressive, especially because it is almost completely 3D printed – even the trigger mechanism. “It has an automatic safety and a Picatinny rail for accessories. It draws 20" and 85#,” Dan explains. The only non-3D printed parts are some aluminum tubes that form the channel of the bolt, while the prod (the bow) is made from PVC, with some fiberglass driveway markers – to ensure it can handle the immense pressure that bows are exposed to. “Combine this with the fact that plastic, especially when 3D printed, is not especially durable, and you have a bit of a design challenge. To prevent the crossbow from breaking, the majority of the stress is placed on the aluminum tubes, which are plenty strong,” he explains.
To ensure that this bow can handle all that power, the part that holds the string (which is subjected to the most pressure) is directly bolted on to the aluminum tube, and not to any plastic. However, all 3D printed parts have been designed in such a way that the layers will not be pulled apart. “The other trigger pieces also need to be strong, but they are only under a direct compressive force, and don't place a shearing force on the housing. All connections between the aluminum and the plastic are bolted right through the tube for maximum strength,” Dan explains.
However, as you can see in the clip above, it is indisputable that the design works very well. Dan understandably does say that he was a bit afraid of testing it the first time. “There was a lot that could go wrong, and I half expected the thing to explode. Thankfully that didn't happen. I did, however, run into a different issue; when the bow was fired the string would go right past the arrow and essentially dry fire,” he says. “This was rather frightening, and the first time it happened it sent the bow flying off of the stock. It's sort of amusing when you test fire a crossbow and the arrow stays put while the actual bow goes flying forward.”
To prevent that from happening every time, Dan secured the bow more solidly to the stock with a spacer – which prevents the string from shooting past the bolt. “Once I made these fixes it worked! Mind you, the trigger is a bit hard to pull (this is due to poor leverage and less than ideal engagement angles), but overall it is a success. I consider this bow to be more of a test than a useful device, but as you can see in the test video, it definitely works! While the 85 pound draw weight is lower than most crossbows, the extra long 20" draw length gives it some extra power, and it hits pretty hard,” he says.
However, he did notice one problem that also affects 3D printed guns. After repeated use, the trigger system becomes less reliable. However, that only occurs after about 50 shots, causing the bow to cock less and less frequently – whereas 3D printed guns can explode after just a few shots. All in all it’s a very impressive weapon that also looks the part. Knights beware. Dan, meanwhile, is already thinking about updating the trigger mechanism to be completely 3D printed and far more reliable.
Posted in 3D Printing Application
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