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Picture of How to Build a Crossbow

The crossbow is one of those inventions that changed history. Prior to its invention, an archer might train for years before developed the strength and proficiency to be an effective warrior. With the crossbow a modicum of training could turn even the meanest peasant into a soldier.  Additionally, through the use of mechanical cocking mechanisms, brute strength was no longer a limiting factor.

All that aside, here's my attempt to design and build a crossbow.

Please note, this should not be attempted by anyone, it can kill you, your dog, your ... etc. etc.


 
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Step 1: The prod, or bow.

Picture of The prod, or bow.
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Fortuitously, I need not replicate this instructable. All you need are the dimensions.

The overall length is 50" with a width of 2 1/2" tapering to 1/2" at either end.  The thickness is 7/16"s.

The nocks, are like the nocks I used previously, how ever instead of tying them on, I used hardwood pins.

Please note, one edge of the bow is kept straight.

I did back the bow, with denim. I simply layed down a coat of Titebond  and then a piece of denim which I rolled into the glue with a dowel, similarly to using a rolling pin.



Step 2: The Stock

Picture of The Stock
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The Stock was whipped up in ProE, it's really just two rectangles, one 3x20 and one 5.5x14.5 offset and joined with a spline to make it "pretty".

So grab the dimensions off the picture and cut out two from3/4 inch ply (it was what was handy)

Once the two pieces are cut, they are screwed together with wood screws, since they will need to be disassembled several times.

Now's as good a time as any to use your jointer to even out the top edges of the two stock pieces, if you don't have a jointer (I don't). screw the stock to a board and just use your tablesaw.  But those top edges must be flat and level.




Step 3: The lock

Picture of The lock
This is somewhat subjective.
Disassemble the stock pieces
Working on the inside face of one piece.
Start by measuring back from the front of the stock 20"s and then down 3/16ths. Use a compass to draw a 1 1/2" DIA. circle.

Measure up from the bottom of the circle 1/4" and then drop that line to the bottom of the stock. Run an orthogonal line from the  end of the line inside the circle towards the end of the stock.

Within this area is where your trigger will be. Can I be anymore vague? Yes. but this will take trial and error. you can see in the pic where I sketched in lines to define the opening.

The hole is where the pivot for the trigger will be.

Step 4: Continuing the lock

Picture of Continuing the lock
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At this point I used a router to clean out the lock area to a depth of 1/4". 

Afterward, I layed a piece of paper over the cut out and traced the outline, because we need to transfer the cut out to the other stock piece.
  Also at this point it is critical to drill a hole at the center of the circle since all your lines will be on the inside when assembled.

Step 5: Stock assembly

Picture of Stock assembly
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Glue and screw the two sides of the stock together, try not to fill the lock cut out with squeeze out. At this point also attach a piece of 3/16" hardwood to the top of the stock, I used a scrap of maple.  Once the glue is dried, use a 1 1/2" hole saw to drill out the hole that the lock position was predicated on.

Then use a belt sand and router with a round over bit to tidy everything up.

Step 6: The Nut

Picture of The Nut
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The nut holds the string when the crossbow is cocked. It needs to be strong and split resistant. To this end I assembled a plywood made from red oak and epoxied together.  Frankly the five layers are not sufficient and this bears rethinking, perhaps interspacing each layer with glass cloth would be better.

Anyhow, once the block from which the nut is being made has cured, it should be turned until it is a slightly loose fit to the matching hole in the stock. About a 1/32nd under is sufficient.

The width of the nut, is the same as the stock minus a hair for tolerances.

The bottom back half of the nut is cut away to form the sear, the top back half to form the fingers that hold the string.  And additional notch is cut to make it possible for the bolt to be in contact with the string.

The nut will be held in the stock with blocks on either side.




Step 7: The Trigger

Picture of The Trigger
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You still have that piece of paper from tracing the lock cutout?  Good because that defines the space that the trigger has to fit and move within.

The top edge of the trigger has to be flat, and the nose square to the top edge, after that, just make it strong enough and small enough to hold the weight of the bow and still rotate to allow the nut to revolve.

I used a piece of hardwood plywood, a poor choice as it's still too splintery. To help fix that I reinforced the end with a carpet nail I found in my shoe.


Once you have the trigger positioned like in the picture, finish drilling the pivot hole, make sure it rotates completely out of the nut hole.








Step 8: Attaching the prod

Picture of Attaching the prod
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To simplify the attachment, I use a bolt through the prod into the stock and securing into a nut hidden in a cross pin.

Step 9: The String

Picture of The String

Is pretty ghetto, it's an endless loop style string made from hemp, it's 48" long and 16 strand. And badly made, hey, it's my first.



Step 10: So what's left?

Picture of So what's left?

Well, it needs to be finished, since it's plywood, I'll probably paint it, since plywood looks terrible stained.

What still needs to be done.

There's no safety.

An index pin to make sure the prod is square.

Pull the screws, drill and plug the holes.

Make a keeper for the bolt, if you tilt the crossbow right now, the bolt slides off.

decent string.

What needs fixing.

Well, I'd hoped to have this ready for deer season, but, that started last week.  I measured the kinetic energy using a ballistic pendulum at 28 Joules, this is below the recommended minimum of 33 Joules for hunting, so I need to make a stronger prod.
I might just glass this one and see what happens.

Alrighty, I'm done.
starseeker1 year ago
How can someone make one of these without all the power tools you used and the knowledge to use those tools? Seems like this is a project to show off skills rather than help someone get ready for a disaster. Geez

I was able to build it with only a drill, file/rasp, hand saw, clamp, and sand paper.

It wasn't easy though, and I messed up a lot of times, but 6 months later I did it.

Well, if you have no skills or knowledge, you can't. Simple as that.

Always wanted to build one

woodstuffs1 year ago

What kind of wood did you use for the prod?

Cryptidking2 years ago
could this be resized with a pistol grip to make a hand crossbow? What other alterations would be needed?
SirBobert2 years ago
What type of arrows did you use? And does the crossbow end up having the 50lb load that the Pyramid Bow had since its the same design? Thanks.
M3G2 years ago
Awesome design!
travw3 years ago
First off, great job. I was having trouble with trigger ideas.

Secondly, what bolts are you using? The bamboo arrows? Have you considered modifying it for use with ball bearings? I think it would be quite doable, and most likely could be undone as well.
zelback1 travw2 years ago
The trouble with the ball bearing idea is that it would have to be weighted directly in proportion to the strength of the crossbow. I am an archery hunter, and I can often be seen at the practice range trying to put six arrows within an inch wide circle from thirty yards. The relevance of this is as follows. By far, the worst injury I have ever seen in a range accident occurred when a guy about three stalls down shattered the crossbow he was using, injuring him, and mortally wounding his spotter. The ambulance came and I watched him get wheeled out on a stretcher with a half-inch thick peice of fiberglass sticking out of his kidney. The reason his crossbow exploded was that he had tried to shoot a bolt that was way too light for the strength of his bow. The result was that all the force that built up upon pulling the trigger rebounded and destroyed the structural integrety of the limbs, which still left so much pent up force that the bow, well, basically exploded. If you were to shoot a ball bearing out of a crossbow and either misjudged the needed weight, or, as seems quite likely due to the nature of the projectile, the ball bearing slipped, you could wind up in a hospital bed, or worse. I would advise you to put some serious thought into this. I later learned that the man who had been spotting for the crossbow-man had bled out on the way to the hospital. I would absolutely hate to think of that happening to somebody else.
MTChar3 years ago
Hey can you please tell us what type of wood you would use for the prod?
Awsome instructable though!
chromestone3 years ago
so we r not suppose to attempt this, it seems you are giving us the instructions to attempt this but at the same time a little unclear the instructions maybe a video of the crossbow in action?
In other words he posted this simply for the sake of knowledge. That and if it kills someone it isn't his fault.
well i wanna build one
mutual wants bro..
FairQueen13 years ago
Crossbows are a great alternative weapon. They certainly have a long history of efficiency as a weapon. This is a great guide to building one.

Recently I've also gotten into air rifles. Not as ancient but much safer than regular guns. There are competitions around the world.
http://www.airarmsairrifles.com
"Recently I've also gotten into air rifles. Not as ancient but much safer than regular guns. "
I've been into air rifles and pistols for over 40 ears, and "much safer" is not too accurate, depending. I've got an air rifle in 9mm and in .45 caliber that would not really be considered "safer" than a firearm. They're used for medium to even large game hunting where firearm ownership is not practical, or illegal for one reason or another.
l8nite3 years ago
I acquired a well abused crossbow recently and of course it needed a new bow. I searched for hours online to ind a crossbow bow with no luck but I did find out that when it was made my crossbow was rather good. I also found out by searching in the parts list that a bow is actually called a limber (who knew?) and is readily available for a nominal fee. Your crossbow is gorgeous, have you been able to use it since you wrote the "ible"?
red-king4 years ago
Great stuff. too bad crossbows are illegal in the place I live in...
Ahhh come on they can't find out who fired it :P
lol
morris102903 years ago
Wow very nice x-bow i actually tried to build my own pellet gun similar to the one here http://ak74airsoft.com/TAPCO-AK47-WOODEN-STOCK-SET-BRWN-LAM-TINTIM06000BRWN.htm but you could barely feel the pellet hit you even from close range... and that's saying a lot considering most ak47 airsoft guns hit HARD. Now if only I could build a penny shooter -.-
nieks4 years ago
Very nice instructable, Allthough I think for my first real crossbow build I wouldn't go for the rolling nut design, because if has a reasonable margin of error. I would choose the notch lock design. It is a bit less pretty, and isn't as smooth as a rolling nut can be, but it almost fool-proof (quite usfull if you are an inexperienced woodworker like me :p )
christpher4 years ago
what do i us to billd the front pes
skimmo4 years ago
this is a great explanation of the nut tigger
Anonbonbon4 years ago
I'm suprised no one has asked this, and maybe it is due to the fact that they can find it, but I can't seem to see where you say what kind of wood the prod is.

May I "prod" at you to reveal what wood it is?

...wow, that was a horrible pun. =_=
Tool Using Animal (author)  Anonbonbon4 years ago
It's red oak, just check out my longbow instructable for details.
Colonel884 years ago
Was the trigger design possibly influenced by...

http://www.pyramydair.com/blog/images/10_11_07_crossbow_trigger.jpg

Also, eventually the sear will wear off, as the trigger holder thing will break it off.
Tool Using Animal (author)  Colonel884 years ago
They cribbed that from here, my original source.  And yes, they'll wear, but are simple to reproduce.

It's the standard design, been in use for a thousand years

seolfor4 years ago
You can also make one using a leaf spring from an automobile. Use the shortest length, and cut it to the same dimensions for your prod. Cut steel rod for the rolling nut, and cut plate steel for the trigger. Braided/twisted steel cable is then us used for the string. Yes, you have to do a lot of hammering to get the leaf flat. However, that was how my dad taught me to make my first one. It had a little over 100 lbs of pull. We used a scrap piece of steel strip to make the bolt holder. Just passing along the info.
seolfor4 years ago
Very nice. I haven't made one of these in almost 2 decades. Thank you very much for sharing. I may have to see what I have available in my scrap pile. :)
yztay4 years ago
I liked your trigger design ;)
Kaiven4 years ago
I saw this and was immediately happy. A sear system crossbow... finally the perfect doable trigger design!
rimar20004 years ago
Very good work, I want to do one like this!!
tfultsucf4 years ago
Well done sir, well done. I'm not going to lie, this really makes me want to make my own = successful instructable.