Pau Amarillo/Yellow heart for "Backing a bow"

[DC]

This is the pic I was referring to. See how the grain goes across the belly in about 4"? That's not good.

[bownarra]

Pau am is no good for backing as Marc said earlier. Reasonable in compression and good for pretty cores but not good for backing.
I hear what you are saying about the bamboo but it sounds like it is too high in moisture content eg. checking after being sanded. Warpage is another issue with too high an m.c.
Your profile is too aggressive (and not in a good way hahah!), as Pat mentioned the kink midlimb is no good. If you must go the r/d route to begin with (and I definitely wouldn't) then get the deflex off the riser then have a smooth curve from inner limb all the way to the tip. The curve should be flatter at the handle and can decrease in radius as you progress along the limb towards the tip.
I would definitely do some straight glue-ups first. The performance will be within a knat's crotchet of the r/d anyway. Your goal should be to learn how to tiller not some fancy profile. Leave them till later
Hickory will work if you can't be bothered to stick with the boo and just want to up the odds of success.
However do not disregard boo in the future it makes an awesome backing when done right.
No need to go finer than 60 grit when using EA40 or most other glues.
Good luck.

[aznboi3644]

I think you may be failing with the bamboo because of your lack of skill and knowledge with tillering high strain D/R bows. Thousands upon thousands of bamboo backed bows have been made. 

[AndyTurner]

This is the pic I was referring to. See how the grain goes across the belly in about 4"? That's not good.

Hi DC, sorry chap I don't know what you mean. Can you mark up the picture please.

Thank you,
Andy

[DC]

If you look between the red lines you can see the split/break going from back(well, the back of the belly lam) to belly. Breaks follow the grain usually. That means the grain is running across the lam in about 4". The drawing shows sorta what I mean. this would be looking from the side. When the grain is like this and it bends it can push the grain apart and one side can slide under the other. Plate tectonics. The grain should go from one end to the other as much as possible.

[AndyTurner]

Ok, I may be wrong - its not unusual, but that just looks like straight grain that literally has been torn apart.

[willie]

Andy,
Have you checked the numbers on your design? you may well be overstrained at the failure locations.
Another possibility. Is all the boo that has failed been from the same lot?

The curve should be flatter at the handle and can decrease in radius as you progress along the limb towards the tip.

Mike, could you clarify please?

[DC]

Ok, I may be wrong - its not unusual, but that just looks like straight grain that literally has been torn apart.

Are you looking at the bamboo or the walnut/ipe(I'm not sure what that is)?

[AndyTurner]

Hi Willie & DC,

DC - I'm really sorry but I have no idea where this is going with the grain. I'm pretty sure the boo & walnut grain are running straight & true longitudinally. I still have the pieces. Tell me which bits you want to see and I will cut them up and photograph. Think Autopsy!!!

Willie - checked what numbers? i thought this whole thing was a suck it and see exercise. I'm just looking at stuff, guessing, testing and analysing the crash!!! Is there a model or some fundamental rule of thumb that I have missed?

Willie - yes, all the boo in the same shipment.

Right, I've been summoned to bed by she that must be obeyed. I'll check in tomorrow.

Thank you all for your input.

Good night,
Andy

[DC]

Can I see a nice clear closeup of the area I marked in red? From the same angle.

[willie]

Willie - checked what numbers? Is there a model or some fundamental rule of thumb that I have missed?

There are a few different modeling tools out there. Three that I know of written by forum members.

If you wish to input lengths, widths and thicknesses, then be able to view a graph of stress anywhere along the limb and at any stage of the draw. then I would recommend VirtualBow. It may be the simplest way to tweak your design if you have areas in the limb with excessive stress. There is a thread here you might ask questions in if you need assistance getting up and running.
 
http://www.primitivearcher.com/smf/index.php/topic,65115.30.html

BTW, the project has since  been renamed, but I think you can still follow the link. Maybe lleroy can update the title of the thread and link, as he is the OP.

The other two are a bit more complex, and you will most likely need to provide more inputs to obtain usable results comparing your broken limb design to a remodel.

All three are capable of building a bow from "scratch" if you are willing to find the data for the inputs. I think mmattockx has a project going now using one of the other two that way.

i thought this whole thing was a suck it and see exercise. I'm just looking at stuff, guessing, testing and analysing the crash!!!

Plenty of folks prefer the old school way of learning, after all this is Primitive Archer

[bownarra]

Willie - so that the reflex will 'uncurl' properly.
Andy - as mentioned at least half of your problems are design related as I mentioned earlier. Just so you know I used to do this for a living and have made close to a hundred r/d bows - my and others advise is good   - learn how to tiller on straight bows. R/d are hard enough to gewt right with a good starting profile.

[bownarra]

Willie - they are also much more stable made this way with less and more evenly distributed strain.

[AndyTurner]

Willie - they are also much more stable made this way with less and more evenly distributed strain.

Hi Bownarra - do you have a picture of a well tillered R/D bow at
1. Unbraced
2. Braced
3. Full draw

So R/D isn't just a "new trendy name" for "recurve"?

Thanks,
Andy

[AndyTurner]

DC - These are the pics you asked about.

I think the grain is straight. I broke this one deliberately just to see what would happen. Both limbs went in the same place - about 7" from fades towards tips.

Thanks chap,
Andy