Introduction: Wooden Desktop Trebuchet

Picture of Wooden Desktop Trebuchet

The trebuchet is a medieval invention originally designed to lay siege to fortresses and castles. The largest of them could hurl immense stones hundreds of yards. Now you can have one to play with in your own home. The whole device stands about foot tall when unloaded and flings various things ten feet or more. Moreover, this is a nice introductory woodworking project that you can do with mostly basic tools. Make sure to check all of the images. A lot of the details are in the notes there.

Step 1: Materials and Tools

Picture of Materials and Tools

3/8" Hardwood Square
1/8" Hardwood Dowel
3/16" Metal Rod
Jumbo Craft Sticks
Wood Glue
Heavy Stuff as a Counterweight

Miter Box
Sharp Knife and/or Chisel(s)
Drill with 1/8" and 3/16" Drill bits

You can really make this project out of just about any type of wood. I chose poplar because it's cheap and sturdy. Most big hardware stores will also have oak and occasionally maple. The design is stout enough that you could make it out of something softer like basswood. In fact, it's probably not a bad idea if you don't have a sharp narrow chisel and you're going to be carving the joints with a knife. These measurements call for just a little over six feet of it. Most 3/8" square is sold in three foot pieces. You might get away with just two if you adjusted the size of a couple of parts, but you'll almost certainly have to recut a couple of pieces so you might as well just get three sticks.

Step 2: Dimensions

Picture of Dimensions

Time to start cutting up all of that wood. We're going to need pieces of the following dimensions:

2 x 6" Long frame side rails - Part A
2 x 3" Short frame sides - Part B
1 x 7" Frame crossmember - Part C
2 x 4.5" Frame extension rails - Part D
2 x 4.75" Uprights - Part E
4 x ~3.5" Long diagonal supports - Part F
2 x 2.25" Short diagonal supports - Part G
4 x ~1" Launch ramp support blocks - Part H
1 x 7.5" Upper Arm
2 x 2.25" Lower Arms

Parts D, F, and G need 45 degree miters cut on each end as shown in the picture. The length measurements are, of course, along the long side.

As for the long diagonal supports (Part F), you'll need to finely adjust the length of these in order to get them to fit nicely. Check the fourth image in step six to see what I mean. The given length of 3 1/2" should get you pretty close depending on how well you cut the frame extension rails.

The launch ramp supports (Part H) are just little bits of scrap that are angled to make a trough with craft sticks. A 45 degree cut isn't quite long enough to attractively cradle a jumbo craft stick so the angle on those is shallower. I just eyeballed it and got something that looked nice. Putting a protractor on it shows it to be about 35 degrees or so. If you don't feel like going through the trouble, you could just glue a couple of craft sticks flat on the frame to make a plank bottom and it'll work fine but won't be quite as pretty and you'll have a little harder time lining up consistent shots.

Step 3: Cutting the Joinery - Part 1

Picture of Cutting the Joinery - Part 1

We're going to employ a lap joint in the long frame rails (Part A). That involves removing half the thickness of the wood at each of the ends so the short sides have something to notch into. Three-eighths of an inch from each end, saw half-way through the stick. Then, using your chisel or sharp knife, cut along the grain to remove the half of the material at the end. You may find it easier to take a little at a time off so you can get it just right. Do the same thing to the other end on the same side.

Parts A and D need cross-lap joints (as does part C, the frame crossmember, but it's a little different so we'll get to that in a minute). To do these, we need to cut out the same amount of wood but in the middle of the stick. Mark it out so it's right in the center. Check the photos to get the orientation right.

Step 4: Cutting the Joinery - Part 2

Picture of Cutting the Joinery - Part 2

The frame crossmember (Part C) is going to seat across both long frame rails so it needs two sections removed. Rather than measure it all out, it's easier to just clamp the four sides of the bottom frame together and lay the crossmember in grooves in the long rails. Get it lined up by eye and mark out the sections where the rails intersect. That's where you're cross-lapping the crossmember just like the rails so mates up tightly and sits flat.

Now we're going to carve the uprights (Part E). One end will have a half-lap and the other end will have a groove carved in the end for the axle to ride in. The half-lap is just like the ones on the side rails. For the axle groove drill a 3/16" hole about half an inch or so from the end. The next step is to clear out the wood between the hole and the end of the upright. Cut a slot from the end to the hole so you can have a little room to get your knife in there and carve it out. Alternately, if you don't mind it being hard to get the arm out, you can just drill a hole a little bigger and thread the axle straight through the hole.

Step 5: Frame Assembly - Part 1

Picture of Frame Assembly - Part 1

You might be able to get away with just gluing all of the parts together but I pinned it all together with glue and poplar dowel; it's not likely to ever come apart and it adds a nice visual element. Clamp together the bottom frame and drill through where ever they overlap. Get a little glue on the joint surfaces and then put a little on the end of your dowel. and work it into your hole and cut or break the dowel off. Once it firms up a little you can shave the leftover nub off with your knife or sand it down. I suppose if you're really bored, you could precut a bunch of little 3/8" and 3/4" lengths of dowel and tap them in. Then you wouldn't need to come back and cut them off.

Pin the uprights to the frame extension rails as shown in the picture. Now is also the time to attach the ramp supports if you've got them. My craft sticks weren't long enough to get all the way across bottom frame, so I supported it in the middle and at the rear.

Once that's all together, you can mount the uprights to the rest of the frame. The frame extension rails run right along on top of the main frame rails. Just glue and pin them in place. Things are starting to shape up.

Step 6: Frame Assembly - Part 2

Picture of Frame Assembly - Part 2

Now here's the tricky part: drilling and mounting the diagonal braces. It helps here to employ the buddy system in order to get a couple of extra hands or to use a bunch of clamps. Either way, try to get your pieces sturdily affixed in a temporary fashion and just drill carefully and slowly. Don't use a lot of pressure or you're likely to force it out of whack. If you've got some patience, you could glue the parts in place and let it dry before pinning.

Step 7: Throwing Arm Assembly

Picture of Throwing Arm Assembly

The arm is easy. The lower arms overlap the upper arms by about an inch and a quarter. You just need to line it up and glue it together. Then you need to drill out the axel holes. The axels will be about an inch and a half apart. It's important that you try to get them straight up and down as much as possible. If you have access to a drill press, I recommend you take advantage of it. You should have a little more than six inches of arm above the main axel depending on how close to the end of the lower arm that you drilled the holes for the lower axel.

The main axels are made from 3/16" steel rod. You could use aluminum if you'd like. It'll be easier to cut but usually costs more. I suppose you could even use a wooden dowel but you'll get a bit more friction. Check the distance between your uprights and cut an appropriate length of rod to serve as your primary axel. Tap it through the hole in your throwing arm. Cut another short piece to go between the lower arms to support your counterweight.

Then it's time to add the release pin. This is the business end of the trebuchet and it's important to mount the pin securely. I used a little length of wire from a jumbo paper clip as my pin. The 1/16" hole I originally drilled to accomodate my pin proved too large. Forcing a bit from a smaller paper clip into the hole along with it made for a nice tight fit. You may even get away with chucking a bit of wire right into your drill and trying to drive it directly into the end of the arm.

Step 8: Finishing It Up

Picture of Finishing It Up

Cut two little strips of craft stick to glue to the sides of the uprights. This will block out the main axel and keep it from sliding from side to side. Make them a little wide so you can trim them down just right.

Then glue down two more sticks to the ramp blocks to make a channel for your payload. If you didn't do the blocks, at least glue a couple of sticks down flat so your projectile doesn't get caught in the frame during launch.

You'll need a weight. It can be just about anything, coins, batteries, stones, etc. What I've found works well, though, is lead fishing sinkers. Specifically, I melted down a bunch of them and put a loop of picture wire in it to make a tidy little weight. Then I sprayed it with a spray-on rubber coating to protect it and make it look nice.

The size of your weight will determine how far your treb will throw. With an eight ounce weight, it'll throw a small binder clip about ten or twelve feet at a height of about four and a half feet. A twelve ounce weight gets a height of about six feet or so with a comparable increase in distance. At a pound or more, it gets to be more than you can practically use indoors unless you're throwing things that are potentionally painfully heavy or you have very large rooms. Of course, with a heavier payload, you'll need a heavier counterweight to get the same distance.

Once you get something together, hang your weight from the the axel between the lower arms of your trebuchet.

Finally, find something to shoot. I haven't found a design for a sling that works well at this size so I just tie a cord to whatever it is I want to chuck. A good length to start with is about four or so inches. Experiment to find what works best with what you're trying to throw.

Step 9: Fire!

Picture of Fire!

To fire your trebuchet, drop your arm into the uprights and hook the loop at the end of your projectile over the pin at the end of the throwing arm. Pull the arm down and place the projectile in the trough. When you're ready to fire, release the arm.

If everything is well, your whatzit will go launching off into the near distance. If your launch didn't go so smoothly, you may be able to do a few things to help it. If your launch is too high or too low, you can adjust your pin or the length of the cord on your projectile.

And there you have it. The whole thing is probably over engineered but it looks nice and works well. In fact, if you wanted to get crazy, the thing could probably hold pretty much as much weight as you could fit though the uprights, easily five pounds or more.

Thanks for looking. This is my first Instructable so I hope it's clear enough for you to make one for yourself if you like it. Please post your comments with any feedback.


Roundcoolkid97 (author)2017-02-02

Thx im building this but its still pretty G A Y

SiggMKE (author)2017-01-25

Been making this for a STEM class that I volunteer with. They're having a blast.

Pierred43 (author)2016-06-27

Hi Is it possible to have the measurements in metric?

Chrisb24204 (author)2015-10-17

For any guys that do shotgun reloading, mix bird shot with melted wax for the weight. You can then make the weight whatever shape and size you want, without worrying about melted lead fumes, since wax melts at a much lower temperature. Anybody that's ever made wax shotgun slugs knows what I'm talking about

doodoo123 (author)2011-07-21

could you give me the sizes of wood i would need to make the trebuchet in double the size. thanks

james.c.andrus (author)doodoo1232015-02-25

Multiply x 2. 3/8 x 2 = 3/4.

Assassin4627 (author)2013-04-05

wow this comment stream is the most epic and longest i have ever seen.

sing1ejack (author)2012-12-21

Thanks for the materials & sizes. To speed things up and simplify it a little I took the side braces off. It still works ok: the uprights are pretty stable, though not as solid as they would be with that third outside brace.

r-philp (author)2012-10-16

My son and I just finished building a trebuchet base in your design. It came out quite well. We made some modifications; We doubled the scale. I was able to make a sling pouch out of denim that released properly. I added a catch to the throwing arm, so I can be cocked, loaded, and finally released by pulling the catch. A bucket of pennies provides the counterweight, although I think we're going to look for an aesthetically pleasing rock.
It took two days to complete, with my son doing much of the cutting, drilling and gluing.
Thank you for writing such a clear instructable. The joinery was a classy touch too!

We're going to build a really big one outside next!

tulekah (author)2009-08-23

WARNING!!! nobody seems to have mentioned that TIRE WEIGHTS contain CADMIUM to harden them. CADMIUM vapor released by melting tire weights is far more dangerous to life than plain lead fumes. I nkow of at least two cases of near-fatal heavy metal poisoning of mountain man types casting flintlock balls from tire weights!!! Me, i used pennies for me weight, easy to fine-tune the range by adding or subtracting a handfull.

Thundermoon99 (author)tulekah2012-10-07

yes but penny fumes also release zinc oxide

Rangemaster42 (author)tulekah2011-12-08

I have melted tire weights in order to cast bullets for more than thirty years. Provided you do it in a well ventilated area there is no danger involved. Tin and antimony are used to harden lead in wheel weights. Cadmium is mostly used for battery plates WHICH SHOULD NEVER BE USED and for cable sheaths.

I am Silas. (author)tulekah2009-09-04

You could also use dead batteries for weights.

ilpug (author)I am Silas.2011-05-18

or a bunch of nuts. the kind that go on bolts, that is.

ryanpriehl (author)2010-01-05

The beginning is for wimps, I use all of the above.

rabbitkillrun (author)ryanpriehl2010-01-16

All of the above is for wimps. I use my bare fists. 

Armestam (author)rabbitkillrun2010-02-04

 All of the above is for wimps, I use none of the above.

rabbitkillrun (author)Armestam2010-02-05

None of the above is for wimps. I use Australia. 

Gksarmy (author)rabbitkillrun2010-04-17

Australia is for wimps. I use the Earth.

rabbitkillrun (author)Gksarmy2010-04-17

The Earth is for wimps. I use the Milky Way. 

red211 (author)rabbitkillrun2010-12-01

the milky way is for wimps. I use my steel toe boots

rastamaun (author)red2112010-12-02

steel toe boots are for wimps. i use mystical unicorn poop that explodes on impact throwing thousands of dolphans in every direction (as they land safley in water after killing my enimies) as the occasional outhouse explodes in the background making it impossible to breathe because of the horrid stench ... but all of a sudden the winged buzzkill comes out of nowhere and flaps its wings to get the stench away so i threw another mystical unicorn poop straight at the winged buzzkill the poop explodes BOOM!!! all is lost for humanity and the earth slowly goes back to when dinosaurs roamed the earth leaving no trace of human kind left until next time.... when god lights up another fart and creates another big boom and creates a new planet for us named superkalifragilisticexpialidoucious-disestablishmentarianismistable. but chuck noris will be spared for he is imortal and we shall see him on our new planet called superkalifragilisticexpialidoucious-disestablishmentarianismistable so he can inspire us all to do it again. :D

red211 (author)rastamaun2010-12-02

mystical unicorn poop that explodes on impact throwing thousands of dolphans in every direction (as they land safley in water after killing my enimies) as the occasional outhouse explodes in the background making it impossible to breathe because of the horrid stench ... but all of a sudden the winged buzzkill comes out of nowhere and flaps its wings to get the stench away so i threw another mystical unicorn poop straight at the winged buzzkill the poop explodes BOOM!!! all is lost for humanity and the earth slowly goes back to when dinosaurs roamed the earth leaving no trace of human kind left until next time.... when god lights up another fart and creates another big boom and creates a new planet for us named superkalifragilisticexpialidoucious-disestablishmentarianismistable. but chuck noris will be spared for he is imortal and we shall see him on our new planet called superkalifragilisticexpialidoucious-disestablishmentarianismistable so he can inspire us all to do it again is for wimps i use my dog to poop on the world

rastamaun (author)red2112010-12-03

useing your dog to poop on the world is for wimps i use my glasses to reflect light into chuck noris's pupil ,wich angers him. so he roundhouse kicks a shiny unicorn so hard that the unicorn literly 'got the poop kicked outta him' wich created a double rainbow wich make me run to the end of the double rainbow wich led me to the lepricons pot of gold , wich was for some reason full of mistical unicorn poop, so i threw it at chuck noris, wich made him so mad that he pooped a brick of pure anger and threw it at me (wich i matrixed out of its way) wich hit the white house and broke all of the huge window,. wich agered Obama so much that he diclaired war on australia. many years of war later canada decided to launch there supergroovalisticprocifunsticationalized weopon of mass awsomeness towards austraila, but chuck noris secretly loves australia. so he super man jumped out of the ocean and punched it with his fist that is secretly hiden behind his beard. causeing the weopen to fly up adn crash into an asteriod that was about to crash into the earth and blow it up to milions of smaller asteriods wich conveniently crashed down upon every one of my enimies, causeing me to win epicly , and giveing a chance for chuck noris to yell "C-C-C-COMBO BREAKER!!!"

Bluesman125 (author)rastamaun2010-12-07

Um, that's ALL for wimps. All of what you wrote, there. Wimpish. ALL o' dat. I use mah titz. AND mah azz. Dat's what I use. - signed, Mae West

skotti666 (author)Bluesman1252010-12-15

your titz and azz are for wimps i would use a super awesome totaly real mega missle to blow up the moon..but in the attempt iron man and superman were having a race to the moon but they saw the super awesome totaly real mega missle and destroyed it then continued on with their race to see who the best super hero was but chuck norris already beat them there making him the most powerfull super hero...but he turned bad and became the worlds most powerfull super villan and he was hell bent on taking over the world but the only ppl he had to kill was my enemies but all of a sudden Dr.Doom comes out of nowhere and challenges chuck to a duel and chuck accepted but little did he know Dr.Doom had every super villan on his side waiting to destroy chuck the battle raged on for hmm about a decade or so untill the victor was the last one standing the rest saw the better...Mr.Rodgers in a bloodstaind sweater...THIS IS THE ULTIMATE SHOWDOWN OF ULTIMATE DESTANY GOOD GUYS AND BAD GUYS AND EXPLOSIONS AS FAR AS THE EYE COULD SEE AND ONLY ONE WILL SURVIVE I WONDER WHO IT WILL BE THIS IS THE ULTIMATE SHOWDOWN (the ultimate showdown)THIS IS THE ULTIMATE SHOWDOWN of ultimate destany

Gksarmy (author)skotti6662011-02-08

this is the biggest TLDR ever

ilpug (author)Gksarmy2011-05-18

meh, i use a cannon.

tami52 (author)Gksarmy2011-04-11

the Earth is for wimps, i use duct tape
i think i just owned everybody here......

bears0 (author)Gksarmy2011-02-08

I... ...AM... ...IRONMAN.

hemley (author)Gksarmy2011-01-11

being mean to Australia is for wimps (im aussie) I burn yooou

son of s8an (author)Gksarmy2010-12-10

everything above is for wimps...... i use pictures of politicians

Fashim (author)Gksarmy2010-12-01

Australia is for wimps. I use a squadron of bears that have steak knives attached to a car battery on there heads.

aagnitsch (author)2011-05-02

I had alot of fun making this. my daughter asked me to make a catapult but thought better of it and this was perfect. got wondering what else i can make with this extra wood i bought before i found this sight. Good work on the instrutions

marc92 (author)2007-11-13

Great Instructable, I love the joinery techniques. I am building one right now. (the glue is drying) One Important thing to be careful of: Lead is a chemical known to the State of California to cause cancer and birth defects or other reproductive harm. Melting lead creates lead fumes which are also toxic. Be Careful For my weight I took a fishing weight (unfortunately lead) and wrapped it with a lead sheet and hammered it together. I plan to encase it in Plasti-Dip when it is finished.

wittzo (author)marc922007-12-12

You wuss, lead was in paint and gasoline for ages and it didn't do any harm to W when he ate it and drank it...wait a minute...:) But really, I melted tire weights to make bullets and cast miniatures lots of times, as long as you don't get it on your skin (youch melted lead!) or wash your hands regularly and wear a mask while you're melting it, you'll be fine. Most of the damage is done when a child is exposed to it...If you're 18, your brain is almost finished, alcohol will do more damage..

marc92 (author)wittzo2008-04-30

My warning also extended to children (I am 15). I'm sure there are many users under 18 on this site who would be fascinated to create this, and be unaware of the dangers lead poses.

jillg (author)marc922008-10-11

try tin weights

red211 (author)jillg2010-12-01

i used a block of steel i got at the local scrap yard

wittzo (author)marc922008-04-30

The plasticote idea is brilliant, though, it keeps the lead from smearing all over the place.. My 8 year old knows that lead is dangerous, she reads about it on warning stickers all the time. She also learned about mercury poisoning by reading about it, but she's smarter than the average 15 year old... If you're old enough to operate a hotplate without supervision, you should have learned by then what's poisonous and what's safe. It's been proven that lead weights and lead bird shot are harmless to the environment. Most of the lead poisoning in nature comes from unregulated dumping or landfills that were grandfathered in before they had such stringent requirements about runoff. The lead from the runoffs (from old paint chips) contaminates the ground water and poisons the animals. If a water fowl ingests a lead sinker or a piece of lead shot, it just passes through. If they survive a shot, their bodies grow a cyst around the shot with no harm. Even today, most doctors keep the bullets in their victims because it will cause more harm to remove them. But lighten up, Francis, you're too young to be such a stick in the mud. :) Girls won't like a guy that acts all tight, I know from experience. :(

photozz (author)wittzo2009-01-25

The symptoms of chronic lead poisoning include neurological problems, such as permanent and temporary reduced cognitive abilities, or nausea, abdominal pain, irritability, insomnia, metal taste in the mouth, excess lethargy or hyperactivity, chest pain, headache and, in extreme cases, seizures, comas, and death. There are also associated gastrointestinal problems, such as constipation, diarrhea, vomiting, poor appetite, weight loss, which are common in acute poisoning. Other associated effects are anemia, kidney problems, and reproductive problems. It has been shown to cause permanently reduced cognitive capacity (intelligence) in children, with apparently no lower threshold to the dose-response relationship (unlike e.g. mercury.)

There's a lot that can go wrong besides brain damage. Although I do notice a strange similarity in the symptoms of lead poisoning and a hangover. :)

red211 (author)photozz2010-12-01

ya it does

Jake_C (author)photozz2009-05-30

wat if im clumsy, throw up sometimes, have sore abs, like after a workout or something, get mad for no reason, can't sleep sometimes, sometimes get a weird taste in my mouth, somedays be lazy, some over active, have slight pains in my chest on occasion, get headaches, and have a chance of seizures, comas, or death. What if i get constipated sometimes, every once in a while get diarrhea, am a picky eater, lose weight if i work out, have a slight lack of iron in my body (one cause of anemia), get a kidney stone, and have a chance to be infertile, or stupid.... that seems like a pretty normal human to me, lol

temp (author)wittzo2009-04-03

The way you said,"as long as you don't get it on your skin (youch melted lead!) or wash your hands regularly and wear a mask while you're melting it, you'll be fine." this makes it seem like" As long as you don't wash your hands, don't wear a mask while melting it, and if you don't get it on you skin you'll be harmed. I think i may just be making this up. But the 18 part is true. It only takes 10 micrograms of lead to cause permanent damage in a developing child. But once puberty is over it's much harder to get it. Considering the entire roman society was based around lead cups and plates and lead based make up, i think we'll be fine.

wittzo (author)temp2009-04-07

I got all sidetracked, the dude is talking about sealing lead tire weights in a tin can that will never see the light of day again. As long as he washes his hands after dealing with them, he's good to go. People make such big, dramatic deal over nothing. To quote Paul Newman,"Hell, the fall will kill you!" Lead is known the world over to cause problems if ingested. My Christmas lights have the warning because the Chinese probably used lead paint, just like any other third world country that figures their populace will probably die of some crazy disease long before they see the effects of lead poisoning. I'll probably die of mercury poisoning from corn syrup before I get lead poisoning, and I smelt tire weights and vaporize lead and other chemicals in the process. I take precautions, but the only way an intact tire weight will kill you is if someone shoots it at you in a bullet or a car careens into you from out of balance tires. Who was the genius that invented lead water pipes? Used lead solder to seal cans? I read that the oil industry introduced lead to gas to improve it's combustion because they had to meet smog standards for pollution control. That's irony at it's best.

temp (author)wittzo2009-04-07

i was just kidding around =0

deathmango (author)marc922007-12-29

Because I was worried about children potentially playing with the trebuchet I constructed (using this excellent tutorial, BTW), I ended up encasing my lead counterweight. I didn't have anything like Plasti-Dip on hand. Instead, I took an old steel padlock and placed it in the bottom half of a small tomato paste can. My PiC (Partner in Crime) and I placed lead fishing weights in the spaces around the lock and melted them with a propane torch (adding more weights as needed). I then cut and folded in the edges of the can, and melted wax over the remaining space above the lead. So the whole set up is sealed in steel can and wax, with the loop of the lock sticking out the top. The only issue that remains is that the folded can edges are a bit sharper than I'd have liked. I think that having some sort of plastic or rubber sealing material is ideal, but if I make another trebuchet, I'll be going back to the Bowl of Abandoned Locks as well.

thepelton (author)deathmango2009-02-27

You could probably put tape over the sharp edges of the folded down can to prevent cuts.

mmmmna (author)marc922008-04-30

Fishing weights ('sinkers') can be found that are made of steel or tin - lead is forbidden in NH waters. FWIW, a scrap padlock (you lost the keys or forgot the combination) should be fine. Folks with some enough space could simply fill a milk jug with rocks and sand and water. Some older men used to collect nuts and bolts... galvanized steel piping could work, Plaster of paris....

thepelton (author)mmmmna2009-02-11

You could have a box at the counterweight point, and fill it with whatever heavy was available. Rocks, nails, metal scrap or whatever. I found that you can find tire weights in the gutters along streets quite often.

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