Bamboo backing for a spotted gum bow.

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albatross
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Bamboo backing for a spotted gum bow.

#1 Post by albatross » Wed Nov 04, 2015 1:02 pm

Hi,
I need some guidance for backing a spotted gum bow with bamboo. I have dressed the bamboo and it is 6-7mm in the centre, i cant go any thinner or I will not have enough width to cover the Belly.
What i need to know is, do I glue on the backing before tillering?
Also what dimensions/thickness should the belly be roughly considering i am backing it with bamboo.
The bow will be 68", 66" ntn and 1.5" wide. I was thinking around 1/2" thick in the middle tapering down to 1/4" at the ends. But this is my first go at using bamboo to back the bow so im not sure.
If anyone has any info it would be appreciated.
Cheers
Matt

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Re: Bamboo backing for a spotted gum bow.

#2 Post by hunterguy1991 » Wed Nov 04, 2015 4:05 pm

Thickness of the limb depends on the design of the bow, ie. flatbow, English longbow etc and the weight you are after with it. Looking at the numbers you gave I'm guessing its a flatbow?

Yes the backing is glued on prior to tillering because the addition of an uneven thickness will change the stiffness in areas of the limb, usually out near the tips.

You can do some tillering before you glue it but usually just up to brace or close to it is as far as you should go, but I normally don't.

The thickness along the limb depends on the tapers of the limb in width also. If you have a parallel with section in the limb the thickness will gently taper f rom handle to tip in that section and then may be parallel for the rest of the limb as it tapers in in width.

Can you post photos of the roughed out belly piece so we can see what the width looks like?

Dave makes a lot of these so hopefully he will chime in and give some pointers.

Colin

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Re: Bamboo backing for a spotted gum bow.

#3 Post by albatross » Wed Nov 04, 2015 6:38 pm

Thanks Colin,
The overall length is 1730mm and the width is 38mm at the widest point, I have left 360 mm in the middle for the handle.(maybe a riser)
685mm in from the end of the limb it tapers down from from 38mm to 16mm, the pics are not the best but i think you get the picture.
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greybeard
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Re: Bamboo backing for a spotted gum bow.

#4 Post by greybeard » Wed Nov 04, 2015 8:08 pm

Hi Matt,

You will need to process the bamboo further before applying it as a backing for the bow.

You have done the first step;

Split or saw your bamboo pole into suitable widths and start flattening the inner surface with whatever suitable tools you have available i.e. belt sander, electric planer, spoke shave etc.

The next step is;

Mark the limb plan [slightly oversize] on the bamboo and cut to shape. Draw marks across the bamboo at six inch intervals as these will be used as checkpoints to control the thickness and taper.

Continue flattening the inner surface until the edges of the bamboo is about 1/ 16” thick. This needs to be done to achieve the desired ratio of thickness between the bamboo and timber stave.

The bottom of the bamboo pole is best used on the lower limb as the nodes are slightly closer which means this section of bamboo is slightly stiffer.

The following links [if you have not seen them] will give you a clearer picture of the ratio of bamboo to timber.

http://www.ozbow.net/phpBB3/viewtopic.php?f=34&t=12874 [Bamboo backed gum longbow]

http://www.ozbow.net/phpBB3/viewtopic.php?f=34&t=13037 [Bamboo/brigalow flat bow]

http://www.ozbow.net/phpBB3/viewtopic.php?f=34&t=15045 [Bamboo and Osage splice]

http://www.ozbow.net/phpBB3/viewtopic.php?f=34&t=15105 [Bamboo and Osage Ozito]

http://www.ozbow.net/phpBB3/viewtopic.php?f=3&t=14895 [Bamboo and hickory curved tips]

http://www.ozbow.net/phpBB3/viewtopic.php?f=34&t=15204 [Bamboo/spliced hickory longbow]

If you feel inclined building in reflex will help to minimise or eliminate 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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Re: Bamboo backing for a spotted gum bow.

#5 Post by hunterguy1991 » Wed Nov 04, 2015 8:11 pm

Your next step will be to trace the bows template onto the flat side of the bamboo as they will be glued. Once you have the template marked out cut it out of the bamboo and continue to thin the now thick edge down to about 1/16th of an inch all the way around. This will in effect taper out the bamboo towards the tips so there is less thickness there and less likely to cause problems with stiffness.

You are on the right track tho mate so I look forward to progress!

Same as Daryl's comments :biggrin:

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Re: Bamboo backing for a spotted gum bow.

#6 Post by albatross » Wed Nov 04, 2015 8:37 pm

Thanks guys,
I have cut the bamboo to shape. The hard part will be keeping it flat as i plane the taper down. It was a challenge just getting the bamboo flat the whole length.
Will update progress tomorrow.
Cheers

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Re: Bamboo backing for a spotted gum bow.

#7 Post by hunterguy1991 » Wed Nov 04, 2015 8:56 pm

Buy yourself a $40 Ozito belt sander from bunnings and stick it in a vice upside down... that's how I do mine, or get a drawknife, they work a treat as well.

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Re: Bamboo backing for a spotted gum bow.

#8 Post by albatross » Thu Nov 05, 2015 7:36 am

Cheers Daryl,
Your earlier post provided very useful info.
Your work is fantastic

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Re: Bamboo backing for a spotted gum bow.

#9 Post by indie » Thu Nov 05, 2015 3:29 pm

Daryl, in looking at your above linked bows it seems if you are backing with bamboo then the grain of the main stave can be far from perfect, yes? This would save me a lot of time at various timber suppliers. :biggrin: Hijack, sorry.

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Re: Bamboo backing for a spotted gum bow.

#10 Post by hunterguy1991 » Thu Nov 05, 2015 6:37 pm

Yea Indie, you can get away with wavy grain if you are boo or hickory backing it. I've backed some atrocious pieces and had them work just fine. Straight is always better but a little bit of character doesn't matter if its backed. :biggrin:

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Re: Bamboo backing for a spotted gum bow.

#11 Post by greybeard » Thu Nov 05, 2015 8:05 pm

Matt,

When flattening the inner of the bamboo pole I have found that a correctly set spoke shave works well but the bamboo can be hard on sharp edged tools.
Spokeshave And Pole Bamboo.jpg
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albatross wrote:Your work is fantastic
Time and patience has its rewards but I would hate to think how many bows I have put into the wheelie bin during the learning process.

Indie,

Pole bamboo as a backing material opens the game when less than perfect timber is the only option. Its use is not a ‘cure all’ for the use of a substandard stave.

Generally, if I have a stave that is not suitable for a selfbow I look at the option of backing it with pole bamboo.

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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Re: Bamboo backing for a spotted gum bow.

#12 Post by albatross » Thu Nov 05, 2015 9:57 pm

Daryl,
I use my electric planer to get rid of the bulk and then my spokeshave and then finished it with the circular orbital sander to make sure it is completely flat.
Glued it to the belly tonight, will post some pics tomorrow

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Re: Bamboo backing for a spotted gum bow.

#13 Post by albatross » Fri Nov 06, 2015 9:19 am

Ok, reasonably happy with the glue up for the bamboo.
I have put 3" reflex in the bow, keeping the middle 320mm handle section flat to the bench, so when I glue on my riser it will be easier.
The handle section of the bow has ended 20mm thick and the ends of the limbs 17mm thick, so 3mm taper on the bamboo basically.
The nodes are as even as I could get them, the node on the end of the limb will be flattened off or removed when I glue my string nocks on, Its around about 1 1/2" off centre.
I will be doing the rest of the bow by hand from now on, because I dont want to use my planer at this stage and take too much off. I also think you get a better feel of the grain this way.
Off to find some nice timbers for the riser, im only going for a 3/4" riser. 3 laminated pieces of timber with very long fades into the belly.
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Re: Bamboo backing for a spotted gum bow.

#14 Post by hunterguy1991 » Fri Nov 06, 2015 12:48 pm

That will go 70-80lbs, maybe more, at those thicknesses, but you have plenty of timber to work will when you are tillering. My 65lb recurve that's all timber with a bamboo back went from 13-11mm in the working limb if I remember correctly.

Make your fades very long and shallow to start with so they can flex a bit then steepen them as they get close to the handle, it will help stop them from popping off.

looking forward to seeing more progress shots

Colin

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Re: Bamboo backing for a spotted gum bow.

#15 Post by albatross » Fri Nov 06, 2015 1:54 pm

Hi colin,
I still have to cut the taper on the limbs which might be a bit more difficult now I have put some reflex on it. The belly thickness is 1/2" at the handle and the outer limbs we be taken down to around 3/8" or some where thereabout.
Quick question, would western red cedar be ok to use for a handle?
Matt

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Re: Bamboo backing for a spotted gum bow.

#16 Post by greybeard » Fri Nov 06, 2015 2:18 pm

albatross wrote:.........The handle section of the bow has ended 20mm thick and the ends of the limbs 17mm thick, so 3mm taper on the bamboo basically........
Matt,

What tis the thickness taper on the bamboo, it is difficult to see it in the photographs, and it looks a bit thick at the tips.

The following photo shows a typical taper rate over 35 inches. The surface appearance of the bamboo was not good but it was suitable for experimental purposes.
Crown At Butt And Tip.JPG
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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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Re: Bamboo backing for a spotted gum bow.

#17 Post by albatross » Fri Nov 06, 2015 2:25 pm

Daryl,
Taper goes from 7mm in the middle to 3-4mm on the outer limbs
Matt

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Re: Bamboo backing for a spotted gum bow.

#18 Post by albatross » Sun Nov 08, 2015 10:13 am

Daryl,
Do you scrape the rind off your bamboo backing or do you leave it natural.
Is there any benefit in doing it, or is it purely for looks eg. Staining it.

Matt

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Re: Bamboo backing for a spotted gum bow.

#19 Post by greybeard » Sun Nov 08, 2015 11:42 am

Matt,

I prefer to leave the rind on as I believe it adds a little more protection against the ingress of moisture. Aesthetically I think the bow looks more natural.

Depending on the profile of the nodes I lightly sand the rough bits but still leave the node proud.

To seal the bow I like to use Minwax wipe on poly, my preference being the satin finish. Bunning's and Masters carry it in stock.

It is easy to use and recoats are easy to apply if necessary further down the track.
Minwax Wipe On Poly Clear Satin.jpg
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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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Re: Bamboo backing for a spotted gum bow.

#20 Post by UPTHETOP » Sun Nov 29, 2015 4:58 pm

Had a look at this thread as have wanted to give the same bow a go. Am going to have a crack at one and just plain see how it turns out. Have no idea what I am doing have cut some boo for backing some spotted gum for the belly and left plenty on everything with the principle I can always take it off. Had a mates self bow so am going off the dimensions of that one and see where it ends up. No form so am only gluing it up half at a time as I don't have enough clamps. Albatross how is the progress going and thanks for the ideas off your thread is all fun.

Cheers Wayno
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Re: Bamboo backing for a spotted gum bow.

#21 Post by UPTHETOP » Wed Dec 02, 2015 11:39 am

Update of where I am. Have cut and rasped the blank to shape. It has about 1/2 inch reflex in it to counter the string follow I hope. Alright the guts. The bamboo backing is not very even through the blank, I tried to start at about 8mm in the middle and half way along the limb 6mm and the tip about 3-4mm. But where the bamboo ribs are the boo is a lot thicker will this matter much when I start to tiller. Also I had to angle the template a little to avoid a knot in one of the tips will this cause twist at all with the grain you could say is not dead strait but cannot be noticed buy the eye at all. The spotted gum is 15mm thick from centre to tips so a lot has to come off the limbs before she will even bend. What taper roughly should I be looking at in my limbs and should I start taking wood off the sides first or concentrate just on the thickness first.
The bow is about 68'' 45mm at beginning off limbs and total thickness with boo is about 25mm.
Am I kidding myself can it be done or am I better off trying to glue up another blank.
Any help would be appreciated.

Cheers Wayno
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Re: Bamboo backing for a spotted gum bow.

#22 Post by greybeard » Wed Dec 02, 2015 12:03 pm

Wayno,

I have found that grain direction in the stave is of less consequence when backed with pole bamboo.

You can take some material off the edges but it will make little difference to the draw weight.

Careful removal of material from the belly is a better option. If you feel confident a two inch hand held belt sander works wonders.

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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Re: Bamboo backing for a spotted gum bow.

#23 Post by yeoman » Tue Dec 22, 2015 5:26 pm

Your effort is not wasted: persevere and you'll get a shooter out of this one.

Don't fret about the variable thickness of the bamboo. It will all work out in the wash.

About 2 inches past the flare, you'll want your limb to be about 15 mm thick, and perhaps 12 at the tips. You've got quite a bit of wood to remove there. Only remove from the belly and leave it on the sides for the time being.

You may find that your reflex increases as you remove wood from the belly, before it starts to take set. A peculiarity of gluing wood in tension, but it's all good. I can explain why this is so or how it happens if there is interest.

Cheers,

Dave
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Re: Bamboo backing for a spotted gum bow.

#24 Post by UPTHETOP » Wed Jan 06, 2016 11:00 am

Thanks for the help fellas is much appreciated.
Well a little progress to date. Put a thin piece of Osage on the belly cosmetics really is only about 2mm thick. Made a string and braced her at 6 inches. There was major tillering in one limb but have got as close as possible to even as I can. Although the limbs do appear to have a little different profile to each other. With one having a small hinge near the tip where a rib from the bamboo backing is present. Have made a tillering board and put her on but have only worked up to 20 inches so far as I don't want to push her to much in one go. After this the bow has received a fare bit of string follow at about 2 1/2 inches but dosn't seem to effect the few short draw arrows I flung out of her. Don't have any scales but it still seems to be on target for around 45-50lb mark, that's if she dosn't explode when she gets out to 26 inches my draw length. Any other help would be much appreciated as I said the limbs do appear to have different profiles on the tillering board.

Cheers Wayno
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Re: Bamboo backing for a spotted gum bow.

#25 Post by yeoman » Wed Jan 06, 2016 3:54 pm

Congratulations on getting the bow bending as far as that. Not long to go now.

If I might lend a little advice:

The outer 1/3 of the limbs are dramatically over stressed. I imagine you've tried to follow a shape of a little bend near the handle, progressing to more bend in the tips. To a degree this is correct, however in this case it's been taken to an extreme. You can get this bow to full draw by only tillering at or around the areas I've indicated here:
Capture bow.JPG
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A small amount of bend here translates to a large amount of deflection at the tip.

By the looks of it, the width taper of the bow looks to be almost pyramid-like. This means the shape of the tiller should be almost circular. Something a little more like this:

Image

See how the change in curvature of the limb is really gradual?

I don't mean to bring you to a point of despair. Your bow will still make a shooter. But your next one will outshine it.

Keep at it, for your own sake and the sake of those at a similar state to you who learn almost as much from the shared experience as you do.

Dave
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Re: Bamboo backing for a spotted gum bow.

#26 Post by greybeard » Wed Jan 06, 2016 7:09 pm

For what it is worth the bow has too much of a rigid handle section and not enough working limb.
Handle Length.jpg
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Judging by the bend near the tips the problem may be terminal. The lower limb appears to have developed a hinge a few inches in from the tip.

The next one will be better.

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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Re: Bamboo backing for a spotted gum bow.

#27 Post by UPTHETOP » Thu Jan 07, 2016 7:12 pm

Dave and Daryl thanks for the advice, will give the areas indicated towards the handle a bit more attention and see if it changes anything, what have I got to loose hey. Has been a great learning curve for shore. Just have to wait for work to slow down before trying another one. Thanks again.

Cheers Wayno
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