Spotted Gum flat bow

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DrAK DaRippa
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Spotted Gum flat bow

#1 Post by DrAK DaRippa » Thu Mar 05, 2015 6:03 pm

this is my spotted gum flatbow so far..
i posted a picture of the stave more than a year ago, i've finally got round to trying to make a working bow out of it. the current picture is of my tillering efforts with a #50 weight hanging from the centre of the handle. it's almost 5" of movement shown in the picture.

as can be seen with the two end photos, one limb has a bit of a longitudinal twist. i'm hoping i can get some advice here, to help me decide a course of action, my ideas are as follows: {1}, over tillering one side of the limb to balance it, and potentially ruining the limb.. {2}, when thinning the tips, shape them as to correct for the twist {3}, ignoring the 'problem' and continuing to tiller the belly flat... {4} steam the limb and apply counter twist from handle to tip.. (i'm not sure about how well i'd do that last one)

so please, if anyone could let me know, is this as big a problem as i'm making it out to be?


i'm also preparing some super fine kangaroo sinew that is rather short, but i'll post about that when i have the hide glue
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woodie
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Re: Spotted Gum flat bow

#2 Post by woodie » Thu Mar 05, 2015 11:48 pm

I think the tips should be thinner as there may be to much mass.
That is just what I think. But is looking good.
Woodie
may your arrows fly straight and true and your limbs return.

DrAK DaRippa
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Re: Spotted Gum flat bow

#3 Post by DrAK DaRippa » Fri Mar 06, 2015 9:18 am

thanks woodie, they will be thinner eventually. i've penned in on the ends roughly how much to remove, i just don't want to thin them out before i know what to do about the twisting that's going on.

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greybeard
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Re: Spotted Gum flat bow

#4 Post by greybeard » Fri Mar 06, 2015 2:39 pm

I do not know if your method of suspending the bow is giving you an accurate reading; 50# at 5 inches [approx brace height] appears excessive.

Perhaps a tiller stick and tillering string may yield a more accurate result? What is the overall length of the bow or planed n to n and what is the total length of the working limbs?

If you can get the bow to brace height without damaging it I suggest you file some string nocks and brace the bow.

This should give a more accurate representation as to what is happening with the limbs and an idea of what correction method will give the best results.

Daryl.
"And you must not stick for a groat or twelvepence more than another man would give, if it be a good bow.
For a good bow twice paid for, is better than an ill bow once broken.
[Ascham]

“If a cluttered desk is a sign of a cluttered mind, of what, then, is an empty desk a sign?” [Einstein]

I am old enough to make my own decisions....Just not young enough to remember what I decided!....

DrAK DaRippa
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Re: Spotted Gum flat bow

#5 Post by DrAK DaRippa » Fri Mar 06, 2015 7:21 pm

well i don't know if it's true of the bows draw weight, but the weight hanging in the middle weighs about 23kgs, and now moves the the handle a bit over 5, enough i think for stringing.

i steamed and untwisted the limb slightly, and thinned the ends and put nocks on too.

as for the sizes, in inches the tips are 10.5'', working limbs are 14'' and the handle is 17ish. just above 66'' in total

the straight line between the ends with the weight currently is 64" and the nocks are an inch down indented on the back like on syahs, rather than on the side. i'll make a 62" string tonight and see how it fits.
would it be wise to sinew the bow before i finish tillering?

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greybeard
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Re: Spotted Gum flat bow

#6 Post by greybeard » Fri Mar 06, 2015 9:12 pm

DrAK DaRippa wrote:........would it be wise to sinew the bow before i finish tillering?
I have not done sinew backing but I believe it would be prudent to have the bow in tiller before applying the sinew.

If the bows tiller goes out after applying the sinew you can remove sinew where needed.

Have you any idea how much the sinew will increase the bows draw weight?

Daryl.
"And you must not stick for a groat or twelvepence more than another man would give, if it be a good bow.
For a good bow twice paid for, is better than an ill bow once broken.
[Ascham]

“If a cluttered desk is a sign of a cluttered mind, of what, then, is an empty desk a sign?” [Einstein]

I am old enough to make my own decisions....Just not young enough to remember what I decided!....

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perry
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Re: Spotted Gum flat bow

#7 Post by perry » Sat Mar 07, 2015 6:03 am

I think a Tillering Stick and Long Tillering String would be a good idea as Greybeard has suggested. I most likely will stand alone on this but I feel you are overthinking the Propelor Twist. I never have been concerned with Propelor's in Bows. I don't understand the endless pursuit with Symmetry that many modern Selfbow makers have. Mother Nature put it there so work with it not against it. Think of it as character and enjoy the challenge.

I doubt the steaming will work, the Tree grew that way and it will not affect the durability or way the Bow Shoots. During Tillering it might work out that you have left a little too much wood on one side of the Bow when Roughing the Bow out which is making it twist a little more

Work with the twist, look at the Twist from different angles. switch the Bow end to end, walk around it. Often a Bow will look out of Tiller from one angle and from another it is perfect. This is the challenge of Tillering a Selfbow. I look forward to watching this Bow evolve

Make sure the Bow is at least Tillered to Brace Height before you back it, even Tillered to 1/2 draw. Back in the 90's I backed a Bow with Kangaroo Sinew, cant remember now if I used Sinew from 7 or 9 Roo's, drove me Nuts processing that Sinew. Under permit I shot the Roo's and it took me most of the Day to cut out the Sinew - stinky rotten Job it was :lol: then the Work Started when I got home. I had trouble with the Bow when it was Humid on the Coast, out West no Drama'. Give it at least 2 weeks for the Sinew to Dry, much longer if it's Humid

regards Jacko
"To my deep morticication my father once said to me, 'You care for nothing but shooting, dogs and rat catching, and you will be a disgrace to yourself and all your family.' "

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Mick Smith
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Re: Spotted Gum flat bow

#8 Post by Mick Smith » Sat Mar 07, 2015 10:23 am

Regarding the twist, I agree with Perry's point of view. While I have never owned a bow with this 'fault', I have seen other archers shooting their propeller bows very effectively over a many year time span. The twist certainly didn't seem to effect their accuracy or their longevity in the least. I wouldn't worry too much about it.

So long as the bow is symmetrical and the string is lined up at the centre of the handle when viewed from directly behind, you shouldn't have any problems, IMO.
There is no use focusing on aiming if you don't execute the shot well enough to hit what your are aiming at.

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Re: Spotted Gum flat bow

#9 Post by DrAK DaRippa » Sat Mar 07, 2015 1:07 pm

now that i've got a string on, a bit under brace height, i can see a hinge for either limb, so i'll have to work around that and make a tillering stick i suppose. the string seems to line up well too.
as for the sinew, i bought some dried thankfully, but its still a pain to process it, especially with how finely separated i prepare mine, i just have to wait for the hide glue i have bought to arrive, so hopefully i'll have this drawing a bit more by the time i can glue on the backing. and Daryl no i don't really know how much it'll increase the draw weight, perhaps enough to counter a natural loss in draw weight after set? just a guess, but if it's excessive i presume i'll have to reduce wood similar to the thickness of the sinew layer?
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cmoore
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Re: Spotted Gum flat bow

#10 Post by cmoore » Sat Mar 07, 2015 2:28 pm

Looks to be coming along real nicely Drak, did you chase the back down to a single growth ring?
Set Happens

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Re: Spotted Gum flat bow

#11 Post by DrAK DaRippa » Sat Mar 07, 2015 8:15 pm

this is from a sapling maybe 5inches in diameter, so after it dried i just removed the bark and split it and have tried to leave the back in its original shape, i'll scrape down a little on it for backing, but i hope to keep the growth ring untouched. here is a post i made midway through last year when i finally split and roughed the stave out.

http://www.ozbow.net/phpBB3/viewtopic.php?f=3&t=14690

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Re: Spotted Gum flat bow

#12 Post by greybeard » Sun Mar 08, 2015 4:16 pm

DrAK DaRippa wrote:... i can see a hinge for either limb, so i'll have to work around that....
Can you rework the fadeouts to give a little extra working limb to reduce the load adjacent to the suspected hinge areas?

If this can be achieved you can then look at reducing the load outboard of the hinge area by reducing limb thickness through to the static tips.
perry wrote:..... I most likely will stand alone on this but I feel you are overthinking the Propelor Twist. I never have been concerned with Propelor's in Bows....
I agree with Perry on this point, I have had flat bows that would look at home on the front of a Sopwith Camel.

The main thing to check for with limb twist is that the bow doesn't throw the string during the draw / release cycle but I don't think this will happen with your Holmegaard style bow.

Daryl.
"And you must not stick for a groat or twelvepence more than another man would give, if it be a good bow.
For a good bow twice paid for, is better than an ill bow once broken.
[Ascham]

“If a cluttered desk is a sign of a cluttered mind, of what, then, is an empty desk a sign?” [Einstein]

I am old enough to make my own decisions....Just not young enough to remember what I decided!....

Dennis La Varenne
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Re: Spotted Gum flat bow

#13 Post by Dennis La Varenne » Mon Mar 09, 2015 8:38 pm

DrAK,

I go along with all above. I am tempted to suggest that you have have narrowed the outer levers to the point where their depth is greater than their width. That on its own will cause twisting if there is even a moderate amount of difference of thickness measured on either sidewall of this kind of bow just after where the shoulders end.

I have had that same thing occur to me as well. The 'fix' was to reduce the thickness of the outer levers such that the cross section was slightly rectangular and always just a tad wider than deep. Those levers do not have to be an obvious feature of the bow. For functionality, they only need to be stiff enough (thickness) to prevent bending.

I don't built these bows with that 'step' you have at the bottom of the levers. I have always just gradually thickened the levers out to the tip starting at the shoulder. That also keeps tip mass down too.

Like all of the advice above, do you tillering on a tiller stick which will impart far more control on the behaviour of the bow's limbs as it is drawn out. Use the long string until you bend it to brace height, then apply the short shooting string or tie your bowyer's knot shorter. And forget sinewing until you have the bow tillered. That will pull it into reflex if you apply enough, but remember that sinew is very heavy - often almost doubling the mass of the bow from the material I have read up on. It is not a good material for long bows because of that. Its best use is on very short bows to impart a lot of reflex for high limb speed.

It would be much less trouble simply to back it with a hickory lamination if you fear breakage. I have a few sinewed longer bows in my collection. These have only the thinnest layer of sinew on them as a backing to protect the back, not as a performance enhancer. They are far too thin to impart any reflex. A hickory backing applied after the bow is tillered to brace height whilst the bow is held in about 4 - 6 inches of reflex (Perry reflex) while the backing is applied offers much more advantage without raising the actual mass of the bow significantly.

In all probability, there would be no actual increased mass by the time you finish sinking the bow during tillering to a manageable draw weight.

Anyway, something to think about.
Dennis La Varénne

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DrAK DaRippa
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Re: Spotted Gum flat bow

#14 Post by DrAK DaRippa » Sat Mar 14, 2015 6:01 pm

thanks for the advice everyone, the twisting was totally fine, when it was strung. i got a tillering stick, but i've unfortunately cracked (not broken) this bow before it was even drawring 12". it started as a zigzaged pinch across the belly of the limb, i thought it was manageable but i've noticed when the bow is being drawn a splinter off the back is lifting.. it's not very large in either case but i've decided that this will only fail early, so i'll try a new project and save my sinew :think:

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cmoore
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Re: Spotted Gum flat bow

#15 Post by cmoore » Sat Mar 14, 2015 6:33 pm

Sorry to hear about the crack....
Do you think you could post pics? As I would still be curious to see , why is it that people seem to be having more success with the kiln dried spotted gum floor boards than they are with staves?....I would have assumed that a nice wide limb shape like DrAK's would be ideal for spotted gum? Perhaps a narrow bow is more suited to it?
Set Happens

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Re: Spotted Gum flat bow

#16 Post by DrAK DaRippa » Sun Mar 15, 2015 12:17 am

i'll post a photo if i can make it come up well on a picture.
and i'm sure i broke it by being too rough with it, i drew it too far by hand unfortunately and heard a crack but it's a learning process and i'll be more careful next time

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