Wednesday, 1 May 2013

How to make a Trebuchet ... ...

Recently we paid a visit to our local museum (well one of them anyway) and as it's a castle of course it has a siege engine (all be it a small one) so we decided we'd have a go at making our own, you can read about our recent visit on my wife's blog - here (opens in new window)

For a rough guide on how to build a small Trebuchet read on.

All you really need to make a Trebuchet is a bit of wood working / diy skill as it involves sawing wood and such like and some tools and a bit of wood.


With a bit of luck you should end up with something like this -


We're very proud of our baby siege engine.

It's not complicated to make, and as to how big you go, well it's up to you, but remember this is designed to fling objects over large(ish) distances, and the bigger you go the further it'll throw (see what I did there ?) I've added a short video at the end of this post so you can see it in action.

Basically I've taken an off cut of an old pine sheet and fixed to it some battens to make a frame, it's a simple triangle shape, with one upright that holds the pivot for the throwing beam, and two supports on either side, clicking on the pictures should bring up a larger version.


The basic framework and base -


You can see that four bits of wood make up the main frame.

From the picture above you can see that the upright ('B') is fixed into the middle of the base, and fixed from underneath and then fixed to part 'A' parts 'C' and 'D' are then cut with 45 degree angles at each end and then fixed to part 'B' and part 'A'

I used screws and wood glue to fix it altogether, and obviously you need to make two sides that are identical.

If you're not too good with cutting wood at angles or the kids are having a go at building something like this, then I'd suggest getting a mitre saw, these can be picked up for about £20 from diy shops, and they come in handy for picture frames and such like, it also means you can do small jobs in the house, I normally use my electric mitre saw, but it's not allowed in the house.


Here's mine, which the kids are getting pretty good at using -


Really easy to use bit of kit.

We added wheels to our trebuchet, but again this is up to you, I added some extra bits of wood to the base so that I could add axles to the back and front, for the wheels I used my largest hole saw, which also leaves an 8mm hole, which is good as I was using bits of 8mm dowel for axles.


Hole saw -


This one needs a sharpen.

Hole saws are great for making wooden wheels, although they do need a bit of sanding to remove any bits of wood that might cause splinters.
In the next picture you can see the wheels, and the extra bits of wood I added to the base.


Wheels (well a wheel anyway) -


We even used small skewers to make pegs.

If you decided to go with wheels you should now have something that looks a little like the next picture, a basic frame on wheels, we'll get to the business parts in a minute.


Basic framework done -


There's really not that much to it.

Originally I was going to use just one piece of wood on each upright, but as the wood I was using was quite thin I decided to go with two bits of wood for each upright.


Like so - 

I could have left it as one piece, but two seemed better.

You can see from the picture I just butted the extra piece up to the framework, rather than adjust everything.

For the the throwing beam and the counter weight pivots I used 12mm dowel, now whilst you need to take care to get everything in line the throwing beam setup needs to be quite accurate, if the holes don't line up and aren't level then it won't throw very well, if you have a post drill then all the better for drilling nice straight holes, but if you don't you can still get things in line by taking your time and using a bit of masking tape (other tapes will do)


Taping two bits of wood to get the holes in line -


A bit of tape works wonders

 You can see in the picture above that I've already drilled one hole, but because I decided to add extra bits of wood I then had to drill holes through them, the masking tape helps to keep everything in line.


Ready for drilling -


Post drills make this kind of thing easier.

 You don't need a post drill, taking care with a normal drill should keep everything in line, and you can buy guides for drills that allow you to drill straight holes.

Once you have the main frame built, you can then move onto the throwing beam and counter weight, these are simple to make, but once again you'll need to keep the pivot holes nice and straight.

For our throwing beam I've used two bits of the batten fixed together, again this is because I felt one piece was a bit too thin, so all I did was fixed the two bits together with screws and some glue, then I drilled two 12mm holes, one almost at the end of the beam, and one 4 1/2  inches (about 11.5cm) further along the beam, you don't want the main pivot hole in the middle of the beam as it'll work more like a seesaw than a Trebuchet.

Our throwing beam ended up being  19 1/2 inches long (about 49.5 cm) with the hole for the counter weight  box 1 1/2 inches (about 3.5cm) in from the end, then the hole for the main pivot 4 1/2 inches (about 11.5cm) further along the beam.


You can see the distance between the two pivot points in the next picture -


It's all down to leverage.

The counter weight box is, well a box, not hard to make, the only difference is that you want to make two sides come to a point (roughly) where the pivot point is, this will allow for more clearance when the Trebuchet is loaded, I miscalculated a little and had to cut a notch out of the counter weight box.


The counter weight box -


Think along the lines of a simple house shape.

Here's the notch I had to cut out of our counter weight box - 


I may rebuild the counter weight box


Again take care when drilling the holes for the pivot, they need to be in line and straight, or the counter weight will sit at an angle, and it'll affect the stability of the Trebuchet, again using tape to hold the two sides when drilling will help keep things straight and in line.


Finishing the two sides of the counter weight - 


We went with a curved design in the end.

We chose a curved design for the counter weight, I'm just finishing it with my homemade spindle sander in the picture, but a simple house shape would do, or even a triangle, but remember to make the box big enough to hold plenty of weight, it's easier to have a box that's too big and have to take some weight out (we used sand,stones and clay) than it is to add weight to a box that's too small.

We used small wooden pegs (made from skewers) to keep everything in line, once we had things where we wanted them we used the pegs to keep things in place, like the counter weight box and the throwing beam, we just drilled (using a small drill bit) either side of the beam and counter weight, then used a small hammer to bang the pegs in, it kind of gives it a more authentic look (well we think it does)


The pegs (on the beam) - 


The pegs make it easy to take apart, should adjustments be needed.

The pegs (on the counter weight) - 


Again the pegs make things easier when it comes to adjusting the weight.

Here's the counter weight box, already weighted - 


We found 1.2kg to be heavy enough.

The clay on top helps stop things flying out of the counter weight box, we found 1.2kg to be about enough on our Trebuchet, but you can experiment with different amounts to see how it affects the range of what ever you use as ammunition.

If you do use screws I'd suggest counter sinking them, and then using some dowel to hide the holes, this is just a case of knocking a bit of dowel into the hole and then cutting it off.


Screw holes hidden - 


An old trick, but it still works.

Apparently these next bits were the most important, least that's what the kids said, I have no idea what they do.


Decoration maybe ? - 


Design features ?

Now comes the important question of the firing system, Trebuchets use a variety of methods, like a wooden basket or a sling, so we've used two different methods, we didn't go with a wooden basket, but we did make a sling (or rather my wife did) she crotched a net from string, which we used to fire the golf ball, the other projectile is a wooden ball on the end of a bit of string, so it works kind of like the hammer they use in athletics.


The projectiles - 


You could use a variety of things, see what works best.


The sling, expertly made by my wife - 


You could always make one out of a bit of material

The next part to the firing system is quite simple, it consists of three pegs, one of which is angled in a specific way, so that the net or the hammer don't release until the throwing beam is upright.


The pegs - 


The one on top at an angle is the important one.

The pegs on either side are where the net fixes to, they aren't used with the hammer, that only needs the angled peg, which is angled in such a way that the net and the hammer won't come off the peg until the beam is upright, otherwise the projectiles would end up go either straight up or actually behind the Trebuchet.


This is how the net fixes onto the pegs - 


A simple sling shot basically.

Hopefully this rather long winded post will go some way in helping you to build your very own baby siege engine.

Here's a short video of it in action, using both the net and the hammer, not the best video in the world, note to self, hold phone other way next time (I may re-do the video)





I'm happy to answer any questions about the Trebuchet, thanks for reading.


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