First bow attempts with Silvertop Stringybark

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AngusB
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First bow attempts with Silvertop Stringybark

#1 Post by AngusB » Mon Feb 14, 2022 7:15 pm

I have been using a fibreglass Mongolian bow for years which is a 45# but thought I would treat myself for Christmas and bought a takedown bow specified as 50#. However on measuring with my luggage scales, I find it close to 60#. I'm not getting any younger and 60# is a fair bit for a casual shooter who just likes to relieve stress in the shoulders and neck by having a few shots at targets at home.

I've been having a go at making a bow with lower poundage so I can do more casual shooting. Ideally something around 35# might be good.
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I keep getting these compression features in the wood. This is the third try. This one is Silvertop Stringybark backed with black bamboo. The first was straight Silvertop Stringybark with no backing and the second was Silvertop Stringybark with a fibreglass mesh backing. I've obviously been checking out a few Youtube videos.

The compression faults occur near the handle. The latest version had a power lam of Blackwood wattle and the flaw has happened just past the end of the power lam (about 3mm closer to the tip). It seems that the slight angle change from the power lam to the straight part of the limb might have caused the problem but it is a very slight change. However this is three times in a row and I'm getting it repeatedly so I wonder what I am doing wrong. Perhaps it's the Silvertop.... might be poor timber for the purpose. Might be prone to this sort of thing. [MoR 143 MPa and MoE 18 GPa, density 860 Kg/m3]. Particularly given that my timber is left overs from a couple of packs that I bought for decking and I used the best bits on the deck, have made garden furniture with the next best and picked the nicest two remaining bits for the bow making attempts.

Any advice would be appreciated. I've got a few pieces of Spotted Gum that look to have reasonable grain and I milled a blackwood log a few years ago but the grain is a little wavy so might cause problems.

I'm a little reluctant to keep going with the Silvertop Stringy but I don't really want to keep making the same mistake with more pieces of timber if it's something I am doing wrong.

Any advice gladly accepted.

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Re: First bow attempts with Silvertop Stringybark

#2 Post by greybeard » Thu Feb 17, 2022 7:50 am

What style of bow are you trying to make?

Could you post an image of the bows edge profile showing the handle, fadeouts and indicate where the limb is failing. Also what shape is the limb cross section and nock to nock length of the bow?

Have you tried a bend through the handle 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!....

AngusB
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Re: First bow attempts with Silvertop Stringybark

#3 Post by AngusB » Wed Feb 23, 2022 10:14 am

Thanks for the reply. Apologies for the delay, I have been travelling.

I guess it's a board bow or a flat bow. I'm not sure what the terminology is. Do the following photos answer your questions? The top attempt is backed with black bamboo from Bunnings
The next one down is backed with fibre glass mesh used for plastering. It was suggested on youtube and, while ugly, I thought it might be worth a try
Third one down is just a piece of my decking offcuts with no other materials
Fourth piece is a blank from the decking.

I'm using the merbau for the handles as I have these scraps from a pallet lying around. I would switch to something nicer looking if I can get the whole thing to work.

I've also got some spotted gum decking, at least one piece of which has grain along the plank nicely.
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The bow with the bamboo is 57 inches from nock to nock
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Re: First bow attempts with Silvertop Stringybark

#4 Post by greybeard » Fri Feb 25, 2022 6:08 pm

It is a little difficult to evaluate a situation from an image.

The first thing I noticed in the images was the abrupt fadeouts of the glued on handle. This has a similar effect of bending a strip of timber over the edge of your work bench.

Has the timber lost its moisture content?

I would suggest a minimum of three inches fade for a shallow handle and lengthen if you go for a deeper handle. The handle needs to transition into the limb to spread the load from the handle.

For selfbows the generally accepted rule is that the n to n length should be double the archers’ draw length plus twenty percent. Naturally this could vary with various timbers and wether they are split bush billets or milled boards.

In the side profile the back and belly appear to be almost parallel and with the plan of the bow the tips appear too wide.

For first attempts I would suggest 68 to 70 inches n to n and bend through the handle design as this gives some leeway to evaluate how the timber wants to respond.

Most importantly what is your tillering proceedure?

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!....

AngusB
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Location: Dandenong Ranges, Vic

Re: First bow attempts with Silvertop Stringybark

#5 Post by AngusB » Fri Feb 25, 2022 6:45 pm

Thanks for the comments.

So I should try,

1. making the handle have a much lower angle (longer fadeout) so there is some bend within the handle fade out
2. have the bow narrow a bit more towards the tips
3. have a bit more decrease in the thickness of the belly wood towards the tips so start with a thicker blank
4. make a longer bow.

I doubt that the timber has lost moisture content too much. It's been outside on my verandah.

I was thinking to cut down the handle shape afterwards but obviously that would be better done first before any exercising of the bow.

I'll see if I can find some a 'bend through the handle' examples on the Internet.

The first thing I did was make up a tillering tree and try not to stretch too far though perhaps I did.

After the first attempt I took to using a portable luggage scales gadget to ensure that I at no stage pulled more than 35 pounds to try not to get the problem again.

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Re: First bow attempts with Silvertop Stringybark

#6 Post by greybeard » Sat Feb 26, 2022 10:45 am

AngusB wrote: Fri Feb 25, 2022 6:45 pm I'll see if I can find some a 'bend through the handle' examples on the Internet.
Perhaps I should have worded ‘bend through the handle’ differently.

Don’t add a handle block or shape a riser. Rely on the thickness of the stave in the ‘grip’ area and it will bend slightly during the draw cycle thus increasing the overall length of the working limbs.

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!....

AngusB
Posts: 13
Joined: Mon Feb 07, 2022 8:46 am
Location: Dandenong Ranges, Vic

Re: First bow attempts with Silvertop Stringybark

#7 Post by AngusB » Mon Feb 28, 2022 7:59 am

Ahh... thanks.

I'm not up with terminology.

Back to the style of my first try. Perhaps I was too rough with the tillering on that.

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Re: First bow attempts with Silvertop Stringybark

#8 Post by greybeard » Mon Feb 28, 2022 10:40 am

Have a look at the following link, quite a good explanation and images.

Daryl.

http://www.primitivearcher.com/smf/inde ... ic=44850.0
"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!....

AngusB
Posts: 13
Joined: Mon Feb 07, 2022 8:46 am
Location: Dandenong Ranges, Vic

Re: First bow attempts with Silvertop Stringybark

#9 Post by AngusB » Thu Mar 10, 2022 5:15 pm

The whole tillering process is stressful after you have already broken quite a collection. Don't really want to keep breaking them.

Before you (Daryl) suggested a simple bend through the handle bow I had already started a couple of others. One was two pieces of wood laminated together. It failed violently when it suddenly delaminated along a big section. It was just a piece of hardware store vic ash that I had and an unknown flexible piece of quite coarse grained timber I got from someone.

The one in the image below is a 70" piece of spotted gum decking pulled at 35lb with a bit of a handle block made out of scrap wood (Bunnings laminated beech).

The boundary between the two boards behind (ie. top of the piece of blackwood) is at about 7 inches from the part of the handle closest to the string.

The shape is not fitting the ellipse terribly well. Should I be taking more material off from the middle outwards focussing more on the left hand side because it hasn't bent as much? Though it looks like the bow (stick) is not sitting perfectly horizontal.

Does it seem that I am on the right track or am I about to ruin another?
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Re: First bow attempts with Silvertop Stringybark

#10 Post by greybeard » Fri Mar 11, 2022 3:29 pm

You need to be more selective in what timbers you use.

Vic ash is a generic term covering various species of eucalypt and probably one of the worst timbers for bow making.

Try sourcing some hickory or hard rock maple from a specialist timber merchant.

Straight grained spotted gum can work and using a wider and thinner limb profile is probably a better option.
AngusB wrote: Thu Mar 10, 2022 5:15 pm The one in the image below is a 70" piece of spotted gum decking pulled at 35lb
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Using a grid pattern behind your tiller stick may help you keep the bending of the limbs more symmetrical.
I found that a four inch grid pattern worked for me. Check to make sure the stave and board are horizontal using a spirit level.
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Once you can safely take the stave two or three inches past brace height fit a string of the correct length. Long tillering strings do not give an accurate picture as to how the bows limbs bend when braced.

You appear to be on the right track, take it slowly and after removing timber gently exercise the limbs so they can settle in.

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!....

AngusB
Posts: 13
Joined: Mon Feb 07, 2022 8:46 am
Location: Dandenong Ranges, Vic

Re: First bow attempts with Silvertop Stringybark

#11 Post by AngusB » Mon Mar 14, 2022 12:26 pm

Kept going with the spotted gum.

Bow has ended up 67.5" nock to nock. String is 66" so too long leaving only 4.5" brace height from handle. Perhaps a one inch shorter string would help. With that string I get 41lb at 24 inches. Haven't dared to go any further since 40lb is more than I wanted. Shot a dozen arrows with it.

It's close, though there are still some irregularities in the tiller part of which is due to a sappy bit in the lower limb which I was worried about. Perhaps I should make myself a tillering gizmo.

Very happy that after many fails I have something that works. Using seconds grade Silvertop Stringybark was doubtless part of the issue. I knew it was a brittle timber from using it for decking. However it was good to learn with. Now I have the other half of the Spotted Gum plank without any sappy bit to work with still.
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Re: First bow attempts with Silvertop Stringybark

#12 Post by flyonline » Mon Mar 14, 2022 6:39 pm

Angus

further to Daryls tillering comments, have a look at this gizmo which should help you get a nice tiller. It is limited to circular tillers, but it has helped me tremendously!

http://www.primitivearcher.com/smf/inde ... 422.0.html

Steve

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Re: First bow attempts with Silvertop Stringybark

#13 Post by AngusB » Mon Mar 14, 2022 9:16 pm

Thanks Steve and thanks of course to Daryl for the help.

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Re: First bow attempts with Silvertop Stringybark

#14 Post by greybeard » Tue Mar 15, 2022 2:25 pm

Angus,

I don’t know if the bow was dead vertical in the photo but you should be able to work out the stiff spots.
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Usually I have found once the bow is braced with the correct length string I can scrape the stiff spots on the belly, every so often exercising the limbs with short draws and this will help the limbs settle in.

When satisfied with the tiller you can sand or scrape the limbs evenly to lower the poundage to the desired weight.

Have the bow about 5#s over the required weight as this most likely will be lost as the bow settles in and takes on some string follow.

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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