Pau Amarillo/Yellow heart for "Backing a bow"

[DC]

Another body on the slab. No.6.

Ok so yesterday I took the pic above. 13b @ 17". Everything looking positive. All I did was dye the back & sand the corners on the belly and back. I drew it back to 17", as per day before, and the boo let go.

Observations
1. The IPE held out. Its still in tact. I'd reuse it but the glue did such a good job some of the IPE is still stuck to the boo & visa versa.
 
2. The boo let go at one of the node points. I've sanded back the other node points and you can see where it broke would have been another node point.

Notes
1. I machined the boo flat to 4.5 mm
2. Using the taper sled, I tapered the boo tips to 3mm. The handle section was 4.5. It fades from tapered to constant thickness somewhere vague in the middle.
3. Prior to machining the boo I took some scrap boo, machined it flat, then tried to break it around the nodal areas. The boo refused to break at the nodal points. I tried around 10 node areas. The boo would fail outside the node area but close to it. This data caused me to think that machining the boo flat would provide a homogeneous material to play with. If it did let go then it would be between the nodes not at the nodes. Ero sanding the nodes would be cool.

Any thoughts?

Don't touch the back of the Bamboo. Not at all. Leave the nodes alone. Try that. If it still fails find another place to get the bamboo.

[gutpile]

I have built quite a few boo backed bows.. I dont sand my nodes either.. I leave them proud . I have a short 56" 55 at 28 boo osage .. reflex deflex screamer.. over 1000 arrows through her.. only boo bow I broke was ipe  boo. r/d.. I was correcting tip alignment with heat ...strung.. hahahaha... I know... no need to comment..... she folded like a piece of paper...gut

[AndyTurner]

...the only other thing I can think of is acetone. I put the purple dye on too thick and used acetone to thin it. It's pretty toxic stuff. I also cleaned up some vinyl patches to fix the hot tub. They both curled up on application. Maybe the boo gets weakened by acetone?

 

[mmattockx]

Andy - Sorry - no idea what any of this means. The belly and back surfaces are flat. They are both tapered. 3mm tip. at the handle, 4.5mm on boo. 6mm on IPE.

To clarify:

The back profile is the shape of the limbs you see if you look at the back or belly of the bow. It shows the limb width and how the limb tapers from side to side from the fades to the tips.

The tiller is the shape of the bend. Yours looks pretty elliptical, which is normal for a bow that has parallel sides on the limbs from the fades out to mid-limb and then a taper to the nocks from mid limb. The circles you show are the correct tiller shape for a pyramid bow where the limbs taper from the full width at the fades straight to the nock. You can tiller most any back profile to any bend shape, but there are optimal bends for different back profiles and it is best to match the two.

If I understand you correctly you machined/ground the outer surface of the bamboo flat? I think that destroys the high tension capacity that bamboo is used for and would likely be why your bamboo failed. Tapering also violates the grain on the face that is tapered. If you put the side out that has the grain violations on it that would also contribute to a tension failure.


Mark

[DC]

Are you grinding/planing the back of the Boo? If so that's your problem. I'd bet a dime on that. I usually only bet nickels

[DC]

I went back and looked at your pictures. I don't see a node anywhere. There's no good pics of the back but any pics that show the back look like its been run through a planer.

[AndyTurner]

Hi Ok,

1. The latest No.6 is a pyramid bow.

2. I did machien the boo flat and then machined a taper.

3. On the previous curvy bow, No.5, constant thickness, I sanded the nodes but left the meat of the lumps in to preserve their strength. This however would have "cost strength" everywhere else. The boo curves across its width. This means its thinner (& therefore weaker) towards its edges. By machining in flat, then machining a taper, I thought I was creating a more "uniform, constant and homogeneous" layer of boo.

4. Fact remains that yesterday I drew it out to 17" and it was fine. All I did today was
1. Twist the string a bit to give a brace height of 5" instead of 3'
2. Apply dye
3. Apply acetone to thin dye
4. Sand the corners on back and belly
Pulling it back to 17" and having it pop on me implies something above caused a weakness and failure.

Regards,
Andy
     

[AndyTurner]

FYI. At the point of break, the boo is 4.5mm. The IPE is 4.7mm. IMO the boo should not have broken due to a "modest" bend.

[willie]

Andy,

You are a more patient guy than me. I would be taking a break (and a pint or three) between bow explosions.

Have you considered a different backing and maybe even a different belly wood to make a 20# bow?

It  seems like at those thicknesses, the bow should be much stronger, and I suspect leaving the boo back natural, nodes and all, will bring different problems with the next one, but sanding them flat is just not a practical option.

In all honesty, a child doesn't need such a complex design. A simple 'D' selfbow will suffice. Kids out grow and accidentally break stuff. 

you can learn a lot about bow building with any size bow, but your materiel's are suited for stronger bows.

[Marc St Louis]

FYI. At the point of break, the boo is 4.5mm. The IPE is 4.7mm. IMO the boo should not have broken due to a "modest" bend.

The Bamboo looks quite flat which leads me to believe that you are planing or flatting the outside of the Slat before gluing it up.  Mark and DC asked you that specifically but you've ignored them both which makes me wonder exactly what is going on here.

[AndyTurner]

FYI. At the point of break, the boo is 4.5mm. The IPE is 4.7mm. IMO the boo should not have broken due to a "modest" bend.

The Bamboo looks quite flat which leads me to believe that you are planing or flatting the outside of the Slat before gluing it up.  Mark and DC asked you that specifically but you've ignored them both which makes me wonder exactly what is going on here.

Hi Marc, I'm sorry but I didn't ignore Marc or DC. I stated,

"2. I did machien the boo flat and then machined a taper."

and

" 1. I machined the boo flat to 4.5 mm
2. Using the taper sled, I tapered the boo tips to 3mm. The handle section was 4.5. It fades from tapered to constant thickness somewhere vague in the middle.
3. Prior to machining the boo I took some scrap boo, machined it flat, then tried to break it around the nodal areas. The boo refused to break at the nodal points. I tried around 10 node areas. The boo would fail outside the node area but close to it. This data caused me to think that machining the boo flat would provide a homogeneous material to play with. If it did let go then it would be between the nodes not at the nodes. Ero sanding the nodes would be cool."

What's going on is, I'm learning from others who are more experienced and knowledgable than me, but at the same time as experimenting proving things to myself in order to gain a thorough understanding and confidence in what I'm doing.

Thank you and kind regards,
Andy

[AndyTurner]

Andy,

You are a more patient guy than me. I would be taking a break (and a pint or three) between bow explosions.

Have you considered a different backing and maybe even a different belly wood to make a 20# bow?

It  seems like at those thicknesses, the bow should be much stronger, and I suspect leaving the boo back natural, nodes and all, will bring different problems with the next one, but sanding them flat is just not a practical option.

In all honesty, a child doesn't need such a complex design. A simple 'D' selfbow will suffice. Kids out grow and accidentally break stuff. 

you can learn a lot about bow building with any size bow, but your materiel's are suited for stronger bows.

Hi Willie, red wine is my soul mate!!!

True I could just make another ratan D-section but I really want to solve this.

I'm only going to change one variable at a time. The next obvious choice is the backing material. For me personally boo is not practical. I'm sure its great when you get the hang of it, or maybe I just got a bad batch as someone suggested. I need something I can machine quickly & easily - I have X5 very keen little customers. I'm thinking Lemonwood now! :0)

In terms of the core wood. IPE is very popular. If you look at the performance numbers on the wood database then I can see why. On paper it performs better than Osage and Lemon wood. I can't find anything better. I don't understand why it's good for strong bows and not light bows too. I've managed to thin it down to ball park performance requirements and on the bows that have shot it felt great. Why would you use a lower performance wood?

Regards,
Andy

[willie]

I don't understand why it's good for strong bows and not light bows too.

equally suited for all, if the bows are kept proportional. just not necessary for such a light bow I guess. Now if you want to make the fastest kids bow at the clubhouse, then you have the right stuff.

[AndyTurner]

I don't understand why it's good for strong bows and not light bows too.

equally suited for all, if the bows are kept proportional. just not necessary for such a light bow I guess. Now if you want to make the fastest kids bow at the clubhouse, then you have the right stuff.

Well just £300 on 3 bits of wood.
..more IPE, Lemonwood & Hickory. Something should work! 

[gutpile]

Andy... get Dean Torges bamboo bow video... appears to me you are flattening the boo at the nodes and that is why your bows keep breaking... watch the video take notes .. will save a lot of time and work... I lightly hit nodes but leave them proud and scrap rine off with scraper.... video will show all.... gut