Pau Amarillo/Yellow heart for "Backing a bow"

[AndyTurner]

PS. Liking the last one best! ;0)

[AndyTurner]

Andy, you are really struggeling hard. I also did (and do) with the r/d design. Only a few things out of my beginners point of view: A) Your design is from the fg-world somehow, not suited for wooden-world. B) The fades are a little steep and abrupt. C) The handle is too big and takes too much of working limb. keep struggeling. I have tried some different profiles and this one now works for me:

Hi SimK. Thanks for the pics.

No worries - I like a challenge. Just get frustrated sometimes.

Ok, so your profile is not dissimilar to mine - just slightly less radical that's all.

The most interesting thing I can see is that when braced and full draw - it looks just like a flat bow. A RC would still look like a RC.

Thank you for that.

Regards,
Andy

[AndyTurner]

Lets see what tomorrow brings
1. Top deck, a failed Ratan project about to become a deflex experiment.
2. Bottom deck. A previously rejected core about to become a flat bow project.

Good night all and thank you for your support,
Andy

[mmattockx]

PS. Liking the last one best! ;0)

I wish that was mine, it is a beautiful piece of work.

Courtesy of silent sniper:  https://www.primitivearcher.com/smf/index.php?topic=65941.0


Mark

[mmattockx]

My plan is
IPE Core - 58". Tip thickness = 3mm. Centre thickness = 6mm.
Yellow heart - 58". Tip thickness = 3mm. Centre thickness = 6mm.

A couple things not mentioned yet:

1) What is your draw length? 58" is very short for a wood bow, especially one with a stiff handle.
2) How long is the handle/riser on the bow pictured?

Aside from tillering an R/D bow as your first project, I think your main problem is not understanding how much weaker wood is than fibreglass and designing a wood bow based on a FG bow. At most, wood can stand about 1/4 the strain of fibreglass. That is for the best woods, the rest are less than that.

Your bow appears to be very short, with a long riser section. This is fine for a FG bow, but will not work in wood. Length is your friend with wood, both in terms of working limb length and using short riser/handle sections. The R/D bow from silent sniper that you liked was 63.25" NTN for a 28" draw with a short stiff handle section and that is considered short for that draw length.

The general rule of thumb for wood bows is minimum bow length = 2x draw length + 10". That gives a 66" bow for a 28" draw. Make your R/D bow 65-66" long and your chances of success will be much, much higher.


Mark

[bownarra]

Yes 58 is too short for even a glass bow. My shortest glass design is 58 and you have to do some funky stuff to make a 58 inch bow work for a 28 inch draw. Most definitely NOT beginner stuff! Refer back to my earlier posts if you want a working bow

[AndyTurner]

My plan is
IPE Core - 58". Tip thickness = 3mm. Centre thickness = 6mm.
Yellow heart - 58". Tip thickness = 3mm. Centre thickness = 6mm.

A couple things not mentioned yet:

1) What is your draw length? 58" is very short for a wood bow, especially one with a stiff handle.
2) How long is the handle/riser on the bow pictured?

Aside from tillering an R/D bow as your first project, I think your main problem is not understanding how much weaker wood is than fibreglass and designing a wood bow based on a FG bow. At most, wood can stand about 1/4 the strain of fibreglass. That is for the best woods, the rest are less than that.

Your bow appears to be very short, with a long riser section. This is fine for a FG bow, but will not work in wood. Length is your friend with wood, both in terms of working limb length and using short riser/handle sections. The R/D bow from silent sniper that you liked was 63.25" NTN for a 28" draw with a short stiff handle section and that is considered short for that draw length.

The general rule of thumb for wood bows is minimum bow length = 2x draw length + 10". That gives a 66" bow for a 28" draw. Make your R/D bow 65-66" long and your chances of success will be much, much higher.

Hello Mark. Thank you for the info.

The bow is for my daughter. She has a DL of 20.5”.
I just guessed at 12” for the riser. Her hand is 3” wide. 1” spare. 2” for fade = 6” x2 (for top of riser) = 12”. I also thought having a slightly longer riser would make it more stable for her.

I’m waiting for the glue to dry on the tips of a new “truly flat” bow.  It’s incredible what happens when you glue the lams together - even with no deflection/reflex!!!!!

Thanks again for your time
Andy

[Marc St Louis]

Wow.  A bamboo backed Ipe bow for a girl? She must be very strong

[AndyTurner]

Wow.  A bamboo backed Ipe bow for a girl? She must be very strong

...well she is my daughter - I’m pulling 70lb @ 28”. She’s got a hairy back too! 😂😂😂

She’s 8 years old. I measured her by trying her out on ratan bows I made for my girlfriends kids. They are a bit older. 10 & 12 yo. She’s pulling about 17lb @20.5”.

The new bow feels quite stiff. A bit too stiff. I figured I’d just tiller it down to desired draw weight.

It’s my son that worries me. He’s 6 and loves demonstrating that he can pull my girlfriends 25lb. Got to love the testosterone fuelled enthusiasm! 😂😂😂😂   

[mmattockx]

The bow is for my daughter. She has a DL of 20.5”.
I just guessed at 12” for the riser. Her hand is 3” wide. 1” spare. 2” for fade = 6” x2 (for top of riser) = 12”. I also thought having a slightly longer riser would make it more stable for her.

Ok, so you should be fine with a 58" bow drawing to 20.5". That mid-limb kink may still have been an issue for you. How far was the bow drawn when it failed?

As noted, 'boo and ipe seem like massive overkill for a 17# bow, you may have issues around getting the limbs thin enough and narrow enough to get down to that weight with materials that stiff.


Mark

[AndyTurner]

The bow is for my daughter. She has a DL of 20.5”.
I just guessed at 12” for the riser. Her hand is 3” wide. 1” spare. 2” for fade = 6” x2 (for top of riser) = 12”. I also thought having a slightly longer riser would make it more stable for her.

Ok, so you should be fine with a 58" bow drawing to 20.5". That mid-limb kink may still have been an issue for you. How far was the bow drawn when it failed?

As noted, 'boo and ipe seem like massive overkill for a 17# bow, you may have issues around getting the limbs thin enough and narrow enough to get down to that weight with materials that stiff.


Mark

Hi Marc,

I'm not really sure. I just put a string on and exercised it progressively until I heard it splinter. It felt like about 20".

I'm making the next one flat to simplify things and get something running. I'll make something curvy after I can make something flat.

This one is pulling 13lb at 17". See attached. (Yes I need to move the bow down the board - show's how much tillering I haven't done yet!!! ROLF :0))

Regards,
Andy

[mmattockx]

I'm not really sure. I just put a string on and exercised it progressively until I heard it splinter. It felt like about 20".

Did you happen to measure the draw weight while you were doing that?

I'm making the next one flat to simplify things and get something running. I'll make something curvy after I can make something flat.

That is a good plan, even flat bows offer enough challenge to get them bending properly.

This one is pulling 13lb at 17". See attached.

The picture is pretty small to see much. What is the back profile? You look to have a reasonable elliptical tiller there but are showing circles for your reference. The bend should be matched to the back profile for the bow to work as well as possible.


Mark

[AndyTurner]

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?

[AndyTurner]

...here's a thought. Maybe I should back it with Unicorn tendons and saw his horn off to make tip & belly reinforcements? Just putting it out there! :0)

[AndyTurner]

I'm not really sure. I just put a string on and exercised it progressively until I heard it splinter. It felt like about 20".

Did you happen to measure the draw weight while you were doing that?

Andy - No sorry.

I'm making the next one flat to simplify things and get something running. I'll make something curvy after I can make something flat.

That is a good plan, even flat bows offer enough challenge to get them bending properly.

This one is pulling 13lb at 17". See attached.

The picture is pretty small to see much. What is the back profile? You look to have a reasonable elliptical tiller there but are showing circles for your reference. The bend should be matched to the back profile for the bow to work as well as possible.

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.

Mark