How to Make a Crossbowgun

About: Engineer from the Netherlands. Projects in 3D printing, electronics, prop making, sewing and whatever interests me. (If you have a pressing question go to my site and ask it there. I am way more likely to ...

In this instructable i will share with you how to make a crossbowgun.

First things first, what is a crossbowgun?
A crossbowgun is a crossbow with a barrel, the main advantage to this is that you can shoot anything that you cab fit in its barrel:
Rocks, pieces of wood, nuts and bolts, fireworks, anything.

This crossbow can be a real weapon, you should never fire this at living things or property that isn't yours.
i won't take any responsibility for any damage, injury or even death caused by this crossbow.

now that we have that part covered, lets move on.

Step 1: The Inner Workings

The crossbow works by stretching the rubber bands, and then releasing all that energy stored in the rubber bands all at once, launching the projectile, just like any slingshot, bow or crossbow.
The unique part of this crossbow is the barrel, with the piston inside pushing the projectile forward.

A few designer's notes
-   Throughout the Instructable you will see that my crossbow has the reinforcements for an ammo slot, yours won't have that. it was a fatal weakness that broke my first crossbowgun, and i had to replace the entire barrel.

-   This is only a rough guide to making a crossbowgun, if you can't get some of the materials in the sizes that i use, just get it in the sizes you can get. the crossbow is designed for materials you can get in the Netherlands.

-   The crossbow is made with rubber bands because it was too hard for me to make a bow, if you think you can make it with a bow, I'd love to see how that worked out.

-   This instructable was made after i finished the crossbow, so i don't have any pictures of some building steps themselves, i will try to compensate for that using drawings.

Step 2: The Things You Will Need

To make this crossbow, you will need the following materials:

-a 40 x 40 x 2100mm piece of straight wood for the barrel (any wood will, as long as it's straight, softer woods are easier to work with)
-a 40 x 69 x 2100mm piece of wood used for the arms
-a 19 x 27 x 2100mm piece of wood used for reinforcements.
-a piece of plywood roughly 10mm thick 
-a 1m piece of 40mm x 3.2mm PVC pipe
-a 1m piece of 32mm x 1,6mm PVC pipe
-a piece of flat steel of between 2 and 4 mm thick for the trigger mechanism
-2 m6 hooks
-a m6 connecting nut
-a hand full of normal nuts and locknuts
-a 20cm piece of M6 thread
-a 1m piece of M4 thread
-M6 washers
-M4 washers
-M4 nuts
-20 small screws
-4 long thick screws
-8 normal screws
-strong glue
-2 heavy duty (5mm) screw hooks.
-2 square hooks (or screws, see trigger)
-rubber bands (a lot of them)
-A solid piece of rubber for the shock absorber (i used a car water hose).

tools needed:

-a drill
-a saw
-2 10mm wrenches
-a 6mm drill
-a 1 or 1,5mm drill
-a 4mm drill
-a countersink drill
-a plunge router
-preferably a dremmel with cutting discs
-an angle grinder for making the trigger

(sorry if i forgot a tool of a piece of material)

Step 3: The Barrel

First things first, we make the frame with the barrel, this is the part where all the other parts are built around.

The first step is to cut 2 1 meter pieces of the 40mm x 40mm, be sure that the wood is really straight or it will cost performance.

In the next step you will have to make a slot in both 1 meter pieces to accommodate the 40mm PVC, the PVC needs to be roughly 10 to 15mm in the wood, so there is a 10mm gap left for the slot in the side of the PVC. you can make the slot using the plunger router.

Note: if you haven't got a plunger router you can also decide to take a thinner piece of wood for the barrel and gluing strips to that piece of wood to achieve the same result.

After that you can place The wood over the PVC to make the brackets.
Cut the brackets to size and place them over the wood. The brackets are in this configuration 90x100mm out of 9mm plywood.
Drill 4 4mm holes through each set of brackets. secure the brackets by putting M4 threads through the holes and securing them with nuts and washers.

Note: at this point it would be smart to number each bracket to mark it's place on the crossbowgun

The next step is to glue the barrel in place using strong glue. this is done by removing the brackets, separating the barrel and wood, gluing the barrel and wood together using lots of glue and then reattaching  the brackets and securing them with the nuts and washers.

Note: it is important to let the glue set properly at this time, you can either wait or make some small separate parts

After the glue has set, use the dremmel to cut the slot in the barrel, do as much of the side as possible before removing the brackets again to prevent the glue getting separated from the barrel. the slot has to be at least 6mm wide for the piston to fit through. After you have made the slot in the ENTIRE barrel, you can move on to the next step.

Note: you have to separate the entire barrel so that it is possible to disassemble the bow in 2 halves and some random parts, else you wont be able to fit the piston and secure the barrel with screws.

With all the brackets removed, it should be possible to reinforce the glue with screws, this is done by:
Separating both halves of the barrel, drilling about 10 holes of 1 to 2mm in each halve, countersinking each of the holes so that there are no screw heads sticking out, jamming the bow, and then securing the barrel to the wood using screws.

Note: when countersinking the barrel, remember: too deep is better than too shallow

Step 4: The Arms

the arms attach to the front brackets by some heavy duty screws and are reinforced by some additional struts.
it is one of the most heavily stressed parts of the bow, together with the trigger, so it needs to be strong.

for the arms you will need an 80cm piece of 40 x 69mm piece of wood and cut it in the middle with an angle of 15 degree, so the  long sides of both arms are 40cm.

next put the arms on the front brackets,predrill and countersink both the brackets and the arms and secure both with 2 long screws (I used 80mm) 

next cut some pieces of the 19 x 27mm piece of wood to make the reinforcement, it just hast to be strong, remember, triangles are an engineers best friend when doing the reinforcements

Step 5: The Piston

The piston is the part that pushes the projectiles forward and connects to the rubber bands.
it is made from 32 x 1,6mm PVC with the M6 hooks and the connector nut and a normal nut.

first cut a 6cm piece of the 32mm x 1,6mm PVC. smooth the edges.

Drill a 6mm hole straight through the PVC, be sure it is straight, if it's off you can't use it.

Next cut the M6 hooks to length so that both hooks will stick about 2 to 3 cm out of the PVC.

Lastly put both hooks through the holes and connect them both with the connector nut with a normal nut next to stop it from coming loose.

Note: If you have problems attaching the rubber bands to the hooks, you can slightly bend the hooks so that the gap will be bigger.

Step 6: The Trigger

the trigger is the most complicated part if you don't have any access to sheet metal and strips of steel.

The idea is to make the trigger look like this, the hooks should be on the width of the center of the piston hooks, all the nuts should be tightened as much as possible for this one part to prevent the separate parts from slipping.

the trigger should be at least 2mm thick, the base plate of the trigger should also be at least 2mm thick.

I used for the thread M6 but you can also use M8 or even M10 if you want to make it stronger.

Apart from that there are no real measurements for the trigger. but just for the idea, my measurements.

after making and installing the trigger, you can fit the square hooks to keep the trigger from going too far up.
you can also use ordinary screws but I like the looks of the square hooks.

Step 7: The Putting It All Together

when you have all parts you can start putting it together. at this stage you can also decide to paint the crossbowgun.

When you are done putting it together you can put some rubber using screws at the end do absorb the impact, i used a water hose from a car to absorb the impact, it works perfect.

Note: The hole at the top is the ammunition hole, its was removed because it was a weakness and had me replace the entire barrel, as seen in the picture, yours shouldn't have this.

Note: as you can see, this bow can't operate without the rubber shock absorbers. please do not forget to install them to prevent unnecessary damage.

Step 8: The Enjoying the Crossbowgun

After all this you should have a crossbowgun. but why stop there, it is a bow with a lot of potential because you can make all sorts of projectiles. So go make awesome ammo on your own and be sure to let me know.
on my side the crossbowgun itself is only the beginning. and for now, enjoy.

Step 9: The Final Thoughts

this is my first instructable, and I had to make it without proper step by step pictures, so sorry if some parts where unclear.

The crossbowgun itself is quite boring without proper ammo, I have already started making some ammo of my own, but I would also love to see your crossbowgun and also what ammo you came up with.
for now: good luck and to give some inspiration i also put some pictures of my current ammo below.



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