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Picture of K'Nex Crossbow
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This instructable shows how to build a working K'Nex crossbow. Please be smart when using this, it can be dangerous. I suggest not using sharp projectiles and not aiming at anyone. I have a few dents in my wall from early testing.

 
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Step 1: Key

Picture of Key
  • Build: build from scratch, unless otherwise noted.
  • Attach: adding pieces to an existing thing
  • Details: nothing new, just a different view

Here are all the parts and names used in this instructables.

Step 2: Parts list

Rods
  • 15 Red
  • 50 Yellow
  • 82 Blue
  • 10 White
  • 95 Green
Connectors
  • 2 White
  • 73 Yellow
  • 5 Gold
  • 11 Green
  • 17 Red
  • 60 Orange
  • 43 Dark gray
  • 35 Beige
Misc
  • 7 Black rod/connectors
  • 23 Silver spacers
  • 36 Blue spacers
  • 2 Hinges
  • 2 Chain links
  • 13.5" Orange track
  • 40" string (any string that isn't too springy, I use fishing line)

Step 3: Starting springs

Picture of Starting springs
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  • 16 Yellow connectors
  • 12 Red rods
TIP: It is extremely hard to snap all of these together at once. Start by using the minimal amount of yellow connectors to make this structure then add yellow connectors one at a time.
 

Step 4: Spring (right)

Picture of Spring (right)
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  • 1 White connector
  • 2 Yellow connectors
  • 4 Dark gray connectors
  • 1 Green rod


Step 5: Spring (left)

Picture of Spring (left)
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  • 1 White connector
  • 2 Yellow connectors
  • 4 Dark gray connectors
  • 1 Green rod

Step 6: Spring (center, part 1)

Picture of Spring (center, part 1)
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  • 1 Yellow rod
TIP: It is hard to snap a rod into three connectors at once, try spreading the connectors out along the red rod so you only have to connect one at a time.

Step 7: Spring (center, cut gold)

Picture of Spring (center, cut gold)
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  • 1 Gold connector


Step 8: Spring (center, part 2)

Picture of Spring (center, part 2)
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  • Gold connector from last step
  • 2 Red connectors
  • 2 Beige clips


Step 9: Main body

Picture of Main body
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  • 47 Yellow connectors
  • 3 Gold connectors
  • 9 Green connectors
  • 4 Red connectors
  • 36 Orange connectors
  • 36 Yellow rods
  • 63 Blue rods
  • 72 Green rods


Step 10: Combining layers and spring

Picture of Combining layers and spring
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Temporarily remove the beige clips attached to the yellow beam on the center of the spring. This will allow you to shift the connectors snapped onto it around, making it much easier to connect the layers.

NOTE: Make sure the gold track guide layer is the center layer, connected to the gold track guide connector which you cut earlier.

Step 11: Trigger housing start

Picture of Trigger housing start
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  • 2 Yellow connectors
  • 7 Red connectors
  • 9 Orange connectors
  • 11 Dark gray connectors
  • 4 Beige clips
  • 2 Yellow rods
  • 6 Blue rods
  • 18 Green rods
  • 2 Black rod/connectors


Step 12: Adding slidebars

Picture of Adding slidebars
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  • 3 Dark gray connectors
  • 3 Red rods
  • 3 Black rod/connectors
  • 15 Silver spacers
  • 6 Blue spacers


Step 13: Finger trigger & mechanism

Picture of Finger trigger & mechanism
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  • 7 Orange connectors
  • 12 Dark gray connectors
  • 5 Beige clips
  • 4 Blue rods
  • 10 White rods
  • 2 Hinges


Step 14: Partially assemble trigger mechanism

Picture of Partially assemble trigger mechanism
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  • 3 Blue spacers
  • Rubber band(s)
TIP: Experiment with rubber bands to find what works well for you. I personally prefer two #32 rubber bands (3-1/4" long when flattened, 1/8" wide)

Note the black connector/rods connecting to the white rods in the second picture. 

Step 15: Trigger housing hinge guide

Picture of Trigger housing hinge guide
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  • 3 Orange connectors
  • 2 Beige clips
  • 1 Yellow rod
  • 8 Blue spacers


Step 16: Trigger housing mid beam support

Picture of Trigger housing mid beam support
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  • 2 Green connectors
  • 3 Orange connectors
  • 3 Dark gray connectors
  • 2 Beige clips
  • 1 Yellow rod
  • 5 Blue rods
  • 3 Green rods
  • 8 Silver spacers
  • 9 Blue spacers
NOTE: Remember to connect the dark gray connectors added here to the ends of the blue rods from the finger trigger.


Step 17: Trigger release

Picture of Trigger release
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  • 2 Orange connectors
  • 6 Dark gray connectors
  • 4 Beige clips
  • 1 Yellow rod
  • 4 Blue rods
  • 2 Black rod/connectors
  • 2 Chain links
  • 10 Blue spacers
Make sure the chain links are oriented correctly. When it is in place (as seen in fourth picture), the hooks should be facing up.


Step 18: Connect trigger housing to main body

Picture of Connect trigger housing to main body
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  • 4 Yellow connectors
  • 1 Gold connector
  • 4 Red connectors


Step 19: Pins & track

Picture of Pins & track
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  • 16 Beige clips
  • 8 Yellow rods
  • 13.5" Orange track

Step 20: String

Picture of String
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  •  40" of string (any string that isn't too springy, I use fishing line)

Step 21: Bolts

Picture of Bolts
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 Parts for one bolt
  • 2 Purple connectors
  • 2 Light gray connectors
  • 4 White rods
  • 4 Blue spacers


Step 22: Done!

Picture of Done!
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Again, I suggest not shooting sharp objects with this, and not ever aiming it at people.

Apart from that, have fun with your new crossbow!

I adjusted a few unnecessary parts and it works perfectly. I also build a nice target and I'm enjoying this. Thanks for the design! (y)
Storm9505 years ago
Nice new trigger system. It looks like the black chain link pieces would be pulled out of the orange connectors if they were pulled so much though. Also I suggest making a new bow (the spring as you called it) such as one powered by counter elastic bands. Check IaC's cannon for reference. Good job.
~KGB~5 years ago
not bad!
AlexWillisson (author)  ~KGB~5 years ago
 Thanks!
no problem!
DJ Radio5 years ago
I can see you at least tried to put effort in it but TBH it's doesn't really have a good design.
AlexWillisson (author)  DJ Radio5 years ago
 I know, but this was something I made on a whim and decided to make instructions. I'm planning on improving the design when I have time.

Also, this is only my first K'Nex weapon. I don't have much experience in designing them.

You could have improved the design before you posted it?
AlexWillisson (author)  DJ Radio5 years ago
 Unfortunately no, I was on a deadline. I figured it was better to get good instructions for a early design, instead of spending forever improving the design. I'm planning on upgrading the design and revising the instructions when I have time. I already have a few ideas for that, also suggestions are welcome.
It's actually better the other way around.
AlexWillisson (author)  DJ Radio5 years ago
 It depends on how far you take it and how long you have.
very good first weapon!
AlexWillisson (author)  Mr. Muggle5 years ago
 Thanks!