Centreshot selfbows

[job]

I had a kind of a query the other day about whether selfbows can be centreshot. Some people say this cannot be because the act of drawing the bow tends to turn the bow in your hand cancelling out any intended bias. I find that in working with split staves sometimes there is a natural curve and shape to the grain that allows the bow to be tillered for Right or Left hand. Here is a couple of pictures that I hope show this. The bottom one is a 30 lber that I let people try down the club. It has a fairly extreme bend that almost becomes RH centreshot when fully drawn. The other is an 85 lbs bow that has a tendency to sit RH . I find this helps with your sight picture on the target.

[Stickbow Hunter]

I have, and have seen, self bows made from split staves and billets which are very bias to left or right hand. Mine is not centre shot but the string tracks to the side of the handle.

Your bows look great.! What wood are you using in making them?

Jeff

[longbow steve]

Hey Job, mine is all but centre shot. Makes it so much more tolerant of arrow spine.

100_4753.JPG (71.34 KiB) Viewed 4620 times

[job]

I have, and have seen, self bows made from split staves and billets which are very bias to left or right hand. Mine is not centre shot but the string tracks to the side of the handle.

Your bows look great.! What wood are you using in making them?

Jeff

I'm using colonial Wych Elm. Kindly provided by the Hobart City Council, happily destroying their heritage.

[job]

Hey Job, mine is all but centre shot. Makes it so much more tolerant of arrow spine.

100_4753.JPG

That is beautiful. I take it it's osage? Did you cut it locally?

[longbow steve]

Hey Job, mine is all but centre shot. Makes it so much more tolerant of arrow spine.

100_4753.JPG

That is beautiful. I take it it's osage? Did you cut it locally?

Yes Job, it is Osage and cut locally. Do you have any in Tasmania? Steve

[job]

Hey Job, mine is all but centre shot. Makes it so much more tolerant of arrow spine.

100_4753.JPG

That is beautiful. I take it it's osage? Did you cut it locally?

Yes Job, it is Osage and cut locally. Do you have any in Tasmania? Steve

Unfortunately not. I heard it's only an American invasion in some parts of NSW. Down here it's an English invasion, hence the Wych Elm. I've tried various local timbers but with only limited success. Wych Elm was supposed to be the No. 1 white wood behind yew, but a lot of folk rate osage as good as yew. Wish I could get hold of some. Love the colour.

[longbow steve]

You could buy seeds of Osage from hardware store in the past for planting as hedgerows/tool handles so it is quite prolific in Vic and NSW. There was a fella in Victoria selling some in the trade blanket but it wasn't prepped with bow making in mind and just felled to be sold by the kilo (probably suitable for turning) Hopefully it isn't all rotting. Cheers Steve

[discord]

There must be some osage down there somewhere, job.. I bought some seeds from a mob in Snug last year. Maybe you could give them a call if you're really keen. http://www.phoenixseeds.net.au/

[Stickbow Hunter]

I'm using colonial Wych Elm. Kindly provided by the Hobart City Council, happily destroying their heritage.

Thanks mate. You will have to show us some more photos of your bows.

No Osage down there huh. I know where you can get some Yew though. Just go through these gates and down on the left.

IMG_2447.JPG (233.05 KiB) Viewed 4586 times

Hope that helps.

Jeff

[longbow steve]

http://www.ebay.com.au/itm/400326568020 ... 260wt_1257
Best get one of these too

[Stickbow Hunter]

Best get one of these too

Yep, that'd be handy for sure Steve. He might need a better silencer on it though.

Jeff

[job]

I'm using colonial Wych Elm. Kindly provided by the Hobart City Council, happily destroying their heritage.

Thanks mate. You will have to show us some more photos of your bows.

No Osage down there huh. I know where you can get some Yew though. Just go through these gates and down on the left.

IMG_2447.JPG

Hope that helps.

Jeff

That's not Yew, that's Huon.

[job]

http://www.ebay.com.au/itm/400326568020 ... 260wt_1257
Best get one of these too

I've heard Government House is the go!. I'll get the muffler, don the ninja gear, and hop over the palings one moonless night.

[rodlonq]

I am no bowyer or even have any experience with selfbows, but I can offer these comments from an engineering point of view.

Unless you have a shelf cut into the bow so that it is past centre immediately above the grip, the bow will not act like it is centreshot, it will act like a straight stave. I am talking about a snakey selfbow here, but has no shelf, just the grip is misaligned with the string as you look at the braced bow. It will draw and shoot just like a perfectly straight stave, with respect to the arrow travelling around the handle.

Visualise a bow that has the limb tips and outer limbs in line with the string but the grip is to the side when you looked at the braced bow from the belly. As soon as you grip the bow and pick up the string, the reaction forces will make a straight line from the centre of your grip (pivot point) to the point on the string where your fingers are. The four points on the bow where forces are acting will want to get themselves arranged into a single plane. So now it is the limbs that will be out of line with the plane that passes through your grip pivot point, the string point and the two nocks where the string pulls on the bow. I would think that unless you have a shelf then the arrow will behave as if it is going around the handle on a straight stave self bow.

Steve's bow above is certainly a special case where the snaky-ness is akin to cutting in a shelf. The pivot point could be either under the arrow if he uses a low wrist or a fair bit to the side if he uses a high wrist. Either way it looks like a really cool self bow and I would love to make one like it one day.

Cheers........ Rod

[Stickbow Hunter]

That's not Yew, that's Huon.

Just go a little further around and I can assure you that you will find this.

IMG_2440.JPG (179.8 KiB) Viewed 4547 times

Jeff

[job]

That's not Yew, that's Huon.

Just go a little further around and I can assure you that you will find this.

IMG_2440.JPG

Jeff

Damn, you've made my day. Nobody would miss one of those limbs would they? If you go down to the woods tonight?

[longbow steve]

I see Jeff has already had a go at it . Steve

[job]

I am no bowyer or even have any experience with selfbows, but I can offer these comments from an engineering point of view.

Unless you have a shelf cut into the bow so that it is past centre immediately above the grip, the bow will not act like it is centreshot, it will act like a straight stave. I am talking about a snakey selfbow here, but has no shelf, just the grip is misaligned with the string as you look at the braced bow. It will draw and shoot just like a perfectly straight stave, with respect to the arrow travelling around the handle.

Visualise a bow that has the limb tips and outer limbs in line with the string but the grip is to the side when you looked at the braced bow from the belly. As soon as you grip the bow and pick up the string, the reaction forces will make a straight line from the centre of your grip (pivot point) to the point on the string where your fingers are. The four points on the bow where forces are acting will want to get themselves arranged into a single plane. So now it is the limbs that will be out of line with the plane that passes through your grip pivot point, the string point and the two nocks where the string pulls on the bow. I would think that unless you have a shelf then the arrow will behave as if it is going around the handle on a straight stave self bow.

Steve's bow above is certainly a special case where the snaky-ness is akin to cutting in a shelf. The pivot point could be either under the arrow if he uses a low wrist or a fair bit to the side if he uses a high wrist. Either way it looks like a really cool self bow and I would love to make one like it one day.

Cheers........ Rod

Very interesting points you raise here. I always assumed that a drawn bow would attempt to align itself in the most vertical plane, which in the case of the very bendy 30 lbs bow I have shown would be in effect to almost turn it on its edge. This bow does not however do that. It just sits there with the string in the same position as in the photo. This bow allows me a true point of aim without aiming off to the side, almost as though it is centreshot. Which is not to say that the arrows are not bending round the handle. My understanding of spine is that all arrows shot with a finger tab bend because of the sideways pressure of a finger release. With a bow shot off the handle the convention is that spine has to be a lot weaker because the arrow has to flex more for clearance as it passes the handle. If it's too stiff it will strike the handle on the way through. The advantage of a bow that is centreshot is that it will shoot a much stiffer arrow and still clear the handle. The other advantage is that the arrow will straighten up much faster, which really helps at short distances where the cycle of the bend can throw the arrow out left or right. Most arrows straighten themselves out over distance, which is why medieval military archers graded arrows by weight, not spine. I'm not suggesting they didn't know about spine, just that it was not relevant to them. Spine as I understand is a fairly modern American concept. I still have the back of the stave that I made the 30 lbs bow out of. I'm hoping to get a much heavier bow out of it. It will be interesting to see if that does turn in the hand. I have a feeling that a heavier bow might, but with that degree of wave there should still be a significant affect on spine.

[GrahameA]

Evening.

.... With a bow shot off the handle the convention is that spine has to be a lot weaker because the arrow has to flex more for clearance as it passes the handle. If it's too stiff it will strike the handle on the way through. ....

You are interested in a couple of things.

# The natural frequency of the shaft so that it effectively goes through one oscillation in the time it takes for the arrow to go past the riser. Spine is an indicator of the stiffness of the shaft which in turn is and indicator of the natural frequency.

# The amplitude of the oscillation so that the arrow clears the obstructions.

[Fraser]

Interesting talking about string bias, my self bow experience is all of 1 week, but when I first strung my bow the string had a very strong bias to the right side of the bow, almost to the edge. After the first 100 arrows the string now sits dead centre of the bow. Also the tiller changed slitely.

Fraser.

[Stickbow Hunter]

I see Jeff has already had a go at it . Steve

Now what gives you that idea Steve?

Jeff