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The trebuchet will be 2 feet tall and the counterweight will be 3.5 lbs.
I don't know if that's any help, but I have used balsa and it broke on us many times. I've used red maple/ redwood and that works pretty good, but it's not in Lowes/Home Depot. A friend got the wood for me and I don't know where to get that around here, so are there any other light yet durable wood we could buy in Lowes/Home Depot?
 

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We have an introduction section for new posters. There you can tell us something about yourself and your woodworking experience.

Just why is it that this wood has to be bought at a Lowes or Home Depot?

The lightest/cheapest wood (if balsa is too weak and for your project that is understandable) that you are going to find is probably white pine. Much will depend upon where you live.

George
 

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If you go to Lowes or HD, you should see a pretty extensive lumber isle for what you're looking for. My local big boxes have poplar, red oak, among others.
 

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I am curious as to why you want to use one of the lightest most fragile woods around .
For a working trebuchet you want strong wood , even for a miniature one that is only two feet high.
Strong wood generally equates to heavy wood , and Hardwoods fit that bill , Balsawood being an exception .
If everything is to scale with the 3.5 pound counterweight , spinning the arm full circle with three and a half pounds in the box and up to , say , one pound in the sling , the strain on the structure will not be slight .

Perhaps Robson will be along soon , he has some experience with these machines of war
 

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Hey MJ! How did you know?

I've built a bunch of Trebs. You can search this place for an old thread.
Pix of my last bigger one. The ones with a ton in the counterweight have long
since rotted to the point that they were firewood. That had to be 7-8 years ago.

Weights: best ratio is 200/1 up to 300/1. That means if you want to build
table-top, banquet busters for ice cubes you need a 8lb lead ball weight off a
fishing downrigger. 8 x 16oz is only 128oz so queen-size olives and cocctail
onions go pretty good for the head table. 1/2 size ice cubes melt and leave no evidence.
I was building those and selling them for $50, weight included.

Throwing Arm: for those, I used straight-grain Douglasfir, about 7/8" square.
Around the axle, I had a piece glued up 3X thick. 1/2" copper water pipe for the axles.
The growth rings in the arm were vertical. Never had any problems with failure.

In the pictures you can see how I built the (red) oak throwing arm with the extra around the axle.
1 lb ice cubes were fun. Nope. Won't explain how the trigger works.

Caution: little ones go off like gunshots. Keep your head out of the way of the arm!
Hope you thoroughly enjoy a little destruction and mayhem.
 

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Steve: part of the balancing puzzle is that the counter weight has to throw the arm, the sling and the projectile. That's a lot of oak mass in the treb that I've kept. I asked Santa for 2 or 3 more 2x2x18 steel bars for Christmas. Stocking stuffers they ain't.

Given the ring porous nature of ash, there could be a lot of elasticity that could whip right over as the sling opens. HMMMMMMMMM Interesting possibility. Since everything else works, perhaps I should make a few different arms.
 

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Poplar and willow are strong flexible timbers .
They used to be used for truck decks when loads were slung of from above , before the advent of forklifts and pallets tearing up the wood necessitated the introduction of steel decks .

How they would take the stress in the pivoting arm is the question .
 

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So, you make a few arms.
So, you break a few arms.
So you learn what works and what doesn't.
Test to destruction. Research.

If I owned a better selection of wood working tools, I'd build an arm from readily available COFI SPF
and hope that it didn't break in the first toss. Every 5 tosses, I'd plane some of it off until it did break.

Right now, just the top 6"/15cm of the shrouded tower sticks out of the snow. Might be a while yet.
 

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I built this out of red oak over 15 years ago. My sons put it through the kid test and it never failed. I remember them saying they had thrown things over 70'.

These pics were taken after he had grown and moved out. The leather pocket and its ropes are long gone but the frame is good as new.




 
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