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Salve,
I have a question for artillery builders and experts! How can I make those vitruvian style curved arms on my upcoming scorpio(70% done) to give it more twist and power? I thought of a metal core for safety reasons, but it wouldn't look authentic so how do I make them out of wood?
Juuso Laasonen
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Two choices
1) find wood grown that way, this will be your strongest choice
2) steam bent, quarter sawn section, grain horizontal
Hibernicus
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When I built my scorpio, I laminated the curved arms out of thin strips. They have held up extremely well. I made quite a massive frame to clamp them to while drying. I only laminated two strips at a time. I was concerned about the grain of the wood not running paralel to the strips, and weakening it. I used a wood called purple heart. It has a tight and quite wierd grain. I kept the form in case I break one of the arms and have to replace it.
Kevin
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Purpleheart? But that's a New World species?
Hibernicus
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Finding two pieces of wood with the natural bend you are looking for would be best, but very difficult to do. I would say steaming. Dry heat might also work, and you need to make a form as part of the bending process.
But whatever you do, if you work down the limbs at all, do not violate the growth rings on the sides of the arms facing away from you (the back of the bow arms). If you do, your arms will most likely explode inward. You will be fine if you shape the arms on the belly side, facing toward you.
Dane Donato
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Thank you for your advice!
Another question if I can ask is what wood should I use for the arms?
Ash?(expensive for me) or some other, maybe Birch?(not so expensive and available easily for me) I have made my scorpio entirely out of birch, and I have planned not to make it as powerful as a ash version would be, what do you think of this solution?
Juuso Laasonen
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I vote for ash.. ash has loads of strength lengthwise.. its a good tool handle for that reason.
Hibernicus
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I agree, ash is the best wood for these machines (and historically correct), but cost are always an issue, eh? I'm fond of birch for arrows, but not for other purposes. However, if you have done the machine in that wood, well....good luck 
But, for safety's sake, consider a bit more expense for the arms. I'd hate to see those arms disintegrate on you. For traditional bows, birch is just terrible, and they explode quite regularly, with just 30 or 40 pounds of draw.
Dane Donato
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We use Ewe aprox 1 3/4" square with a iron bar along its length, it can handle the 1 ton pull on the machine and are straight.
http://www.romanarmy.com/cms/component/ ... temid,137/
This one has similer thickness arms 
Regards Brennivs
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Caratacvs
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You said "Ewe", but you meant "Yew", didn't you?
Not to make a pun, of course.
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Ash trees can be found across Finland. Maybe a source could be a landowner who needs one trimmed or will let you lop off a couple of select branches, or a tree trimming company or firewood supplier.
Either way, I agree: do not scrimp on such a vital element of your machine.
Hibernicus
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OOPS Demetrivs I must have had sheep on my mind :lol: :lol: :lol:
Regards Brennivs lol:
Woe Ye The Vanquished
Brennvs 390 BC
When you have all this why do you envy our mud huts
Caratacvs
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Thank you again for your expertise on the matter!
Only thing that is currently holding me back on getting the ash arms is the rarity of these fine trees here in Finland and the Finnish law, which protect them because they are so rare. Only source for me is currently the local wood shop(200 meters away from my home!) but it is very expensive to get such a small amount... the other option I thought about was making the arms from steel (very strong I suppose) and coat them in wood so it would look correct (ash is of course the best option if I can find it somewhere). What opinions do you have on this?
Picture of my birch frame:
![[Image: 016934.jpg]](http://www.pienoismallit.net/media/kuvat/01/69/34/016934.jpg)
Juuso Laasonen
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Quote:OOPS Demetrivs I must have had sheep on my mind :lol: :lol: :lol:
Regards Brennivs lol:
What are you doing with that ewe Brennivs, ohhh  hock: eeeeeeew!
Visne partem mei capere? Comminus agamus! * Me semper rogo, Quid faceret Iulius Caesar? * Confidence is a good thing! Overconfidence is too much of a good thing.
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Byron Angel
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Soem thoughts:
Check out a furniture maker as a source.
Perhaps the experts at the lumber store could recommend an alternate wood species.
Maybe laminate alder with oak. Or birch and oak.
Hibernicus
LEGIO IX HISPANA, USA
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