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Wood Axels

Started by JP Wazz, May 03, 2011, 08:40:00 PM

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JP Wazz

I am building a trebuchet-style catapult and need advice on wood selection for the two pivot axels, one for the main pivot point of the throwing arm and another for the counterweight. I have an 8"x8" beam from a green ash tree that I cut down last fall. From this beam I need to saw out a  3" x 3" piece for the 2 axels. My question is, am I better off sawing out the heart of this timber or using wood from the edges? Oh yeah, I should mention that the counter weight will be about 1800# and the longer axel will be about 30". JP.

tyb525

JP, With ash I think either would work, however the juvenile wood near the heart may be less durable and strong. Also, wood closer to the outside of the tree will be clearer.
LT10G10, Stihl 038 Magnum, many woodworking tools. Currently a farm service applicator, trying to find time to saw!

bill m

Rick Brown from the Handshouse studio has built wooden timberframe cranes. He might have some suggestions.
NH tc55da Metavic 4x4 trailer Stihl and Husky saws

Raphael

... he was middle aged,
and the truth hit him like a man with no parachute.
--Godley & Creme

Stihl 066, MS 362 C-M & 24+ feet of Logosol M7 mill

laffs

which country are you going to invade?
timber harvester,tinberjack230,34hp kubota,job ace excavator carpenter tools up the yingyang,

JP Wazz

To Raphael, what is the advantage of using the heartwood? JP. 
To Iaffs, no invasions planned but I do have some annoying neighbors that I may be able to intimidate. JP

Ianab

With the size of the beam you have you should be able to saw out the axle "free of heart" and that should be the strongest.

There are two ways to approach it. Either keep the "pith" in the middle of the piece, but you still risk the wood splitting. Do that if you have a smaller piece that only just makes the axle.

Or cut a piece from the best clear wood, away from the pith. That will be more stable and should have less knots (potential weak points)

Ian
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

Raphael

I was thinking bigger than 3" when I made the suggestion as I'm used to working with larger wood.   ::)

The advantage in a boxed heart is the checks stop at the heart rather than going all the way through, and shrinkage is 'symmetrical'.  At 3" it might not matter much either way but I'd let a FOHC blank dry fairly well before shaping it.
... he was middle aged,
and the truth hit him like a man with no parachute.
--Godley & Creme

Stihl 066, MS 362 C-M & 24+ feet of Logosol M7 mill

Stan snider

Assuming this is an outdoor project have you ever thought about longevity? Ash has low decay resistance and can be brittle.

It you get the urge to throw some boulders or whatever a couple of years from now you would be a lot safer if this was white oak, hedge or  mulberry in these parts.

Hedge would be the standout choice for strength and decay resistance.

Stan

thecfarm

I want to see a picture of that. Even better will be a video of it in action.  ;D
Model 6020-20hp Manual Thomas bandsaw,TC40A 4wd 40 hp New Holland tractor, 450 Norse Winch, Heatmor 400 OWB,YCC 1978-79

fred in montana

Ironwood if you can get it. If not, black locust is super hard and decay resistant.
woodmizer lt15, mf 65 tractor
logdovetailjig.com

JP Wazz

As far as the variety of wood goes, I gots what I gots. The trees were free for the cutting:1 green ash, 1 white oak and 1 burr oak, my biggest expense to date was for the sawing which at 80$ I believe was very reasonalbe considering that he came to me. Misfortunately, or not, the largest longest beams came from the ash and I do have options for treating or preserving the wood as well. JP.

Raphael

I'd go for as many white oak parts as possible in that case.
... he was middle aged,
and the truth hit him like a man with no parachute.
--Godley & Creme

Stihl 066, MS 362 C-M & 24+ feet of Logosol M7 mill

JP Wazz

The main frame work will be all oak construction, the larger timbers white oak and  the smaller planking members burr oak. The counterweight framing is oak as well, boxed in with ash. The throwing arm was my ash largest beam measuring 8"x8"x11'. JP.

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