Introduction: K'nex BJ-2 Combat Knife Mods

Picture of K'nex BJ-2 Combat Knife Mods

Structural and aesthetic modifications to the K'nex BJ-2 Combat Knife (from Battlefield 2142) which goes with the Morretti SR-4 K'nex Recon Kit
Picture 1/2: Modified Knife
Picture 3: Original Knife (You may want to build the original knife first

Step 1: Mods to the Handle

Picture of Mods to the Handle

This might be hard to assemble. Insert white rods throughout the handle, and remove the Y connector from the original. My recommended method:

Picture 2: Build the parts like this (Add white rods to the connectors in the middle layer. This isn't shown in the pictures. Make sure you replace the two red connectors in the front of the handle with green connectors.
Picture 3: Different angle
Picture 4: Attach by the middle connectors. You may need to remove one layer first, but reattach it afterwards. Add a blue spacer on the lower grey rod. This will go in front of the white rods that will soon come.

Reattach the green and white rods to the outer layers of the handle.

Step 2: Mods to the Blade

Picture of Mods to the Blade

Add 22 orange connectors between the grey rods
Add 8 blue spacers to the front.

Step 3: You're Finished!

Picture of You're Finished!

Credit to Imperar for the 3d modeled K'nex pieces.
I uploaded the model I used to make the instructions:
With the mods, this is the best K'nex knife on the site so far. It's very sturdy and durable (I've thrown it against the wall a few times, without it breaking.) But try not to stab too hard, because:
A) With enough force at an angle, the light grey connector will snap off and you'll have to gather the blue spacers (happened to me a few times). Ironically, the front is the weakest part of the knife, but as long as it doesn't hit at an angle, it stays on well (I've tested it by stabbing a piece of wood).
B) You might hurt someone if hit in the right spot
C) both
I trust you can be careful enough with it.
If it need be said, I take no responsibility for anything done with this knife (or really, the mods).
You might have guessed, but this is my first instructable. Please give advice or corrections. By the way, be as harsh as you want. I like reasoning.


LvNo1000 (author)2013-03-12

I lose 8 mini spacers every time the unreenforced top pops off? meh. Other than that its pretty awesome 4.7/5

ted816 (author)2008-04-21

what program did you use to make the pictures?

BrazenRain (author)ted8162008-04-23

I used Google Sketchup. If you have it, you can find the model here

RangerStorz (author)BrazenRain2012-10-10

nice knife dude, works good!

sandmman (author)BrazenRain2010-12-31

omg realy. how did you make all the sizes perfect, that must have taken days

This is the BEST knife I've ever seen on ibles'.

Knexmechanic (author)2011-03-23

i made a holder for it

kohokillerx4 (author)2010-11-07

very nicely made

charleszxc (author)2010-03-13

wats the knife on

charleszxc (author)2010-03-13

i like the colors

KnexFreek (author)2010-02-23


stevoIution (author)2008-09-21

1. an instrument for cutting, consisting essentially of a thin, sharp-edged, metal blade fitted with a handle.

nobody cares wether it cuts or not. its for looks.

BrazenRain (author)stevoIution2008-11-10

1. A weapon consisting of a metal tube from which a projectile is fired at high velocity into a relatively flat trajectory.

Looks like my knife fits in perfectly with k'nex guns. I doubt anyone would make it for cutting anything...

P.S. I know this is late. I haven't been checking back to this instructable.

knex gun maker (author)2009-07-02

funny name (bj)2

tjzx3432 (author)2009-05-01

i made a sheath for it

054629 (author)tjzx34322009-05-21

Can you Show us how to make it

tjzx3432 (author)2009-05-01

tight instructable best one yet

hoi (author)2009-04-26

First: It is an PERFECT knife!!!! it's strong and with an good handle! but do you have an holder for it???? that would be great!!

Gun Maniac (author)2008-12-07


gremlinz_man (author)2008-11-25

it makes my gun look even awesomer!!! =)

Pat Sowers (author)2007-12-27

Looks good! i can use this to work on my knife tricks! Thanks!

BrazenRain (author)Pat Sowers2007-12-28

The center of gravity is just around the white connectors, so it will work for that. A personal favorite maneuver of mine is one seen in Resident Evil 4 in an encounter with Ada. From the regular position you would hold a combat knife (pointed outward, the two grey connectors near the white connector are pointing down) rotate it around the back of the handle so that it's horizontal and the two grey connectors are facing away from you. The point will be facing to your right (if you're using it with your right hand). (Shortly afterwards, Leon holds the knife to Ada's neck before she can aim her pistol)

Pat Sowers (author)BrazenRain2008-02-01

I just made this knife and I rocks! the only thing is every time I swing in the blade comes flying off!!!! I use swords so swinging this thing is fast as S***!! I think thats why it is flying apart. any idea of how to make it stronger?

BrazenRain (author)Pat Sowers2008-02-03

Does the blade come completely off or does one of the grey rods get detached? If so, does the top or bottom rod come off?

Pat Sowers (author)BrazenRain2008-02-03

both rods come off.

BrazenRain (author)Pat Sowers2008-02-04

Lol I don't know what the say... almost. Check the pieces, if the white connector is bent a little (the rod shouldn't slide in and out too easily), and make sure all the pieces are connected to start with. Or you could be slashing way too hard. Ouch... What exactly are you slashing?

Pat Sowers (author)BrazenRain2008-02-04

all the peces are connected strongly. And im just slashing the air..........LOL

BrazenRain (author)Pat Sowers2008-02-05

...I've stabbed and slashed wood and it doesn't disconnect unless I slash really hard at a bad angle. You didn't build the original without the mods, did you? Or build from mini K'nex? Or build out of some amazing paper K'nex which pointlessly falls apart? Lol, just throwing around a few ideas. Finally, check that all the white rods that connect the layers are connected (and present in the first place).

DrWeird117 (author)BrazenRain2008-11-09

Okay, I downloaded Google SketchUp, and how do I do a search for K'nex?

BrazenRain (author)DrWeird1172008-11-10

I have a link to Sketchup's Warehouse (which is quite hard to find; I haven't found it without using Google search lol). That link goes to my knife model. Type knex in the search bar there and it will bring up a bunch of other knex models (and it looks like it's not just Imperar and me anymore).

DrWeird117 (author)BrazenRain2008-11-10

Okay, cool. Thanks!

Pat Sowers (author)BrazenRain2008-02-05

i looked and it still does....... idk this is still a cool instructable! nice job!

BrazenRain (author)Pat Sowers2008-02-06

Thanks. If you still want to resolve that problem, try replacing the grey rods, and experiment with your own modifications, like replacing the light grey connectors with red connectors (and adding a white rod) or green connectors (two white rods) or some other modification. It's all about diagnosing the problem, which I can't exactly do since I don't seem to have it.

Pat Sowers (author)BrazenRain2008-02-06

i will give it some work.

BrazenRain (author)BrazenRain2008-02-04

Oops I meant if the yellow connectors are bent. Check the white one anyway.

Sypran (author)BrazenRain2008-02-03

same here! i love that seen! even though im curently using this knife as a beonet i wish i could move that fast and do that (but i gess since knex r usaly bolt action i gess it can happen)

Pat Sowers (author)BrazenRain2007-12-28


Gun Maniac (author)Pat Sowers2008-02-03

nice mods i originally posted the instructions for this great weapon.

Guardians38 (author)2008-10-13

how did you make the annimated version of it?

jayg5000 (author)2007-12-29

That is a pretty neat looking knife not to mention the sketchup images of it. That is very impressive.

Gun Maniac (author)jayg50002008-09-23

With Thanks To Me! lol Thats my knife

MI6 (author)2008-08-29

i like this for my bayonet

Cybeast-Ichigo (author)2008-08-11

I made four of these before I ran out parts for them.

Hehe, nice. Four of the same thing may get boring. I suggest try varying them a bit. Shorter blade, shorter handle; an incredibly short handle with a long blade; or a 'boxcutter', long handle with a short blade. Just some things to make it fun.

I was inspired to do 4 by General Grievous from Star Wars: Revenge of the Sith.

apples!!!!! (author)2008-07-26

i love it. its great for airsoft wars sometimes too.

mettaurlover (author)2008-05-20

bodinbro (author)2008-03-04

want to know wat? some one should make a sheath for this that would be awsome!:)

BrazenRain (author)bodinbro2008-03-04

I'm ahead of you with that. =P I've tried a few different designs for making a sheath. Some of the main problems are size, stability, being able to attach to the knife, and weight. Even if it was successful, it would probably be something you would throw aside while whipping out the knife because it looks cool. As for the bayonet idea, a k'nex rifle really isn't that good for bayonets. You usually end up breaking the (probably detachable) bayonet off or getting a few pieces of the gun to fly off. There just isn't enough strength in such a long k'nex structure like a rifle. While it would look cool, it really wouldn't have any functionality, and might get in the way of other parts of the gun, such as the sights.

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