So to be clear I personally would consider this more of a giant sling shot then a balista. Due to the fact that it is powered by rubber bands instead of a bow. And why did I build a balista you are probably wondering... Well It was a Tuesday I was really board, and when I get board my mind starts thinking off all the things I could be building and that day my mind was on cross bows! So I'm like what the heck i am going to build a giant cross bow! I know I have way to much time on my hands...
So I hope you like it! And as always I love hearing all of your opinions and thoughts!
Step 1: The Stuff You Need! Tools/Materials
As far as what I used, I basically walked around my shop and yard and picked up all the trash and pieces of scrap from random projects.
So I ended up with a few 2x4s
about 15 feet of old oak barn siding
I used surgical tubing that my mom had, its the same stuff they use on sling shots and it worked very well.
some old chain
I have a lot of scrap steel laying around from blacksmithing so I used pieces of bar stock and angle iron
some old bolts and nuts
screws 3" and 2 1/2''
and I painted mine black just because black bows look cool! And it was kind of the only color spray paint I had. Unless I painted it yellow and I really was not seeing a bow that looked like a troll had peed on it....
A drill, I just recently got a 20v Dewalt impact driver, and It was a very good investment, and is one of my favorite power tools i own.
Table saw, or chisel if you really want to go the brico bart way and use all hand tools. :P
Angle grinder with cut off wheels
Wrenches for making sure all your nuts are nice and tight
A square for marking your angles, the square is that triangle marking device for all those who dont know.
And some patience, lets just say the reason it took so long to post this was becasue there might have been a few strings broke and 2x4s thrown...
Step 2: The Base
So I am sorry for not having detailed instructions for building this part. This is the base to my old trebuchet that was kind of small and did not ever work right. But the base it self is pretty self explainable. So I used this opportunity to teach my little brother how to use a angle grinder and let him sand it all smooth he did a good job for his first time.
After that was all cleaned up this is what I ended up doing.
I took two pieces of angle iron and screwed them to the sides so they made the whole base taller. Then I cut another piece to bolt across the two angle iron uprights so that the bow would have something to rest on.
After I got the angle iron on, I used some old oak barn wood and started filling in the frame, just to make it look more solid and add more strength. This ended up making the base close to 30 pounds more heavy.
Keep in mind that this whole project was off the top of my head and I did not give it to much forethought so I will make a list of all the stuff I should have done at the end.
Step 3: The Bow...
Like I said I would not call this a bow myself its more of a T shaped thing to hold the string but it works.
I took a 2x4 and cut a grove in it for so the bolt had a guide. I did this with a table saw if you dont have a table saw your could do this all with a chisel. then I took another board for the "bow" i made mine 4 1/2 feet wide and 5 foot long. And to add stability I put two 45 degree braces in.
Step 4: Mounting the Bow
I made the this so that i could swivel the bow witch enables me to aim a little.
First I took a bolt and cut the head off with my angle grinder then I drilled a hole in between the two braces, and I took that bolt a threaded it into the hole. just make sure that the pin is somewhat strait.
Now this part took a lot of time to get it to work right but I got it all figured out for you now. I took about a 4" piece of pipe and flattened one end of it and drilled a hold through the flattened end. then bolted that to the center of the angle iron cross piece.
Then take your pin and slid it in the pipe. if you did not know thats how it worked then you might want to check your self. just sayin
Step 5: The Triger
Now this is thee most complicated part of the whole thing! I ended up useing a design that is almost the same as some of the knex guns I used to make when I was little. The basic Idea is that the wheel holds the string and then you have a lever holding all the presser on the back side of the wheel.
The first thing you need to do is take a piece of bar stock and cut out your wheel. And drill a hole right in the middle!
Then I took another bar that was from some sort of garden steak and I was to lazy to cut it all flush and grind it down all pretty so I just kind of started cutting the wheel so it fit in nice and snug.
After your wheel is snug you have to get something to hold it all together. i used two 2x4s drilled some holes put two pins in and then lined my lever and wheel up. you also need a lot of washers to make sure the spacing stays the same.
I added a lot of pictures of this so you could see everything well.
Step 6: Putting It Together.
Once you have your base bow and trigger your can slap it all together!
I mounted my trigger first, when you do this make sure that the wheel is facing the right way, and that it is just above the track so that the sting locks in nice and tight. another thing I had to do to the trigger was make two cut outs so that i could pull the string back into the wheel.
From there you can add what ever you want to it really more bracing, wheels, spikes, chains, and other decorations. I kept mine pretty simple.
Step 7: The String
This was the most painful part of this build. I ended up having two strings snap on me and that did not feel to good! in fact it kind of hurt and I might have got really mad at it. but after a few tries I found that taking two of the bands and twisting them together made it a lot stronger and it stopped snapping.
To string the bow I just drilled to holes in the end of the bow and ran my tubing through them. and pulled them pretty tight the bow was about 50 Lbs of pressure by the third time I strung it.
by the end I was very happy with it though it took a while to get it all fine tuned and working smooth, but she fired every time after I was done!
Step 8: Final Thoughts
So I liked this little project I did, It turned out great i think. Not really the most butiful thing but i was never aiming for the most beautiful crossbow.
If I could redo it I would have spent the day blacksmithing instead. but then there would never be this instructable...
I think I would change my bow to something flexible ether PVC or i would have taken some Osage and made a bow for it.
I would have defiantly made a little more fine tuned trigger this one works great but it could be way smother.
But in the end i got it to shoot about 75 yards witch was good!
Well thank you so much for looking at my instructable! And anything you have to say about it or questions please ask away! I love hearing from everyone.
And I Would appreciate your vote if you feel this is worthy!