Another mad project!

[MattZA]

Update:

We have achieved brace height! Put another 50 or so arrows through it at half draw.

There is a problem forming though. When glueing up my belly lam, I somehow managed to make a dent in the belly. After shooting, I've noticed it's starting to lift under compression.

Any ideas? I'm considering a bamboo patch to take the strain off.

Here's a braced photo. I wrapped some cotton thread around the handle, mostly to make it easy to find the damn handle at a glance 

It's got a cool shape at brace height, I think.

Thoughts?

[Halfbow]

I'm unsure what you mean. A dent is starting to lift? Can you post a close up?

[MattZA]

Ha ha, I was just typing you a PM!

Unfortunately it isn't really visible unless braced - and I don't want to do that again until I've fixed it.

Picture it like a small knife slash across the belly (about 1/4" wide). It's not very deep, but you can imagine how it'll behave under compression. It isn't lifting, per se. It's more compressing the affected fibres, which is causing them to lift about 1/2" down from the cut (in the handle direction) I think it was caused by a shim sitting awkwardly during glue up.

Put your hand flat palm down on a surface. Keep your hand on the surface and try to slide your index finger towards your hand. The cut is at the end of your finger nail, with the lifted knuckle where the fibres are lifting.

[MattZA]

Hands up who else just tried the finger thing... 

[Halfbow]

*hand up*

Ok I understand. Huh. Interesting. Can't say I've had that problem before. Under the lifted part, is it the glue line that failed?

I would try to get some thin CA glue in there. Super glue could work if you can get it in the right places, but the water thin stuff would be ideal to really soak in and saturate the area. Then I'd wrap it tight with string, and soak the string with glue too.

Since bamboo varies in density so much from the inside of the culm to the outside, your 3 lam bow has an interesting layer cake of different densities throughout its thickness,  If you tried to do any kind of patch where you cut out a chunk from the belly and insert a new chunk of material, I might worry about some eventual problems stemming from unmatched densities.

[DC]

Did you scrape the outside of the boo where ever it was going to be glued? Boo has a waxy outer coating that I'd bet glue won't stick to.

[MattZA]

*Edit* If you zoom into the photo until about 350-400% you can see a slightly raised dark spot on the right hand side of the handle.

Halfbow: No unfortunately it's not the glue line that failed. The cut effectively severed some of the top fibers on the belly. The resulting weakness effectively allowed the cut fibres to start lifting at the depth of the cut. Almost like when peeling a banana - the skin and fruit separate along the grain lines where the original 'break' was made.

Hmm, I'll give CA a shot. I don't have very high hopes, because I tried a similar thing with TB3 when I first saw the cut and fibres just hinting at lifting. They got covered in TB3, clamped closed, and left overnight. All seemed fine, until I noticed the fibres now lifting closer to the handle, but still in line with the grain from the original cut.

It's almost as though the TB3 prevented them from lifting there, so the force simply carried on down the grain until it could find a place weak enough to actually separate the fibres within the lam.

I like your idea of soaking the whole bastard in CA, though. The CA weight shouldn't affect bow efficiency much, since the cut is about an inch above the handle.

DC: I did scrape the waxy layer off. It didn't break along the glue line, though. It's only lifting as deep as the cut (which is very shallow. We're talking maybe three sheets of standard A4 printing paper, here).

[Halfbow]

Ok I see. So you're basically dealing with a running crack. Definitely don't want to be chasing it incrementally across the whole bow, but I'd think that if you can stabilize it all the way to the end of the crack, that should stop it from spreading more. Maybe the first time it went farther than you realized.

I've used CA as a finish before, and you may not know what you'd be getting yourself in to. >< If you try to cover your whole bow, you better get what you want in a few quick long smooth swipes. Otherwise it will quickly devolve in to a fumey sticky mess that gets worse the more you mess with it. It's a great covering for smaller things, but it's difficult to execute well on bigger things. Of course if you'll be wrapping your bow with felt.. that gives a lot more leeway on how it looks.

Just to mention, tb3 doesn't stick to its cured self very well. It may not matter much in this context, but in case you're thinking of using it again to try to fix it, it could be unideal to use it again where it's already been.

[MattZA]

This is becoming a build along! If any admins read this, feel free to move the post over there if it's annoying y'all 

Well I very liberally applied CA to the crack area last night. Not that it needs to set overnight, but I only looked at it again this morning. It does seem to have stabilised the area well.

I'll only know for sure at brace/draw though. I'll continue tillering as soon as I finish carving proper string bridges that don't look like a Lego left in the sun.

[MattZA]

Hi all,

Just an update on the little bugger.

I haven't had the time to do much work, but in tillering I noticed a hinge was forming where the aforementioned running crack was.

To remedy this I glued a small bamboo patch onto the belly and then glued and wrapped some silk ribbon around it a few times.

Unfortunately that didn't have the desired effect. It did however cause the opposite limb to bend more evenly with the repaired one. This has given a unique appearing set, because the cotton I used as a temporary handle (photo above) actually prevented any set in the handle.

I have since removed all the wrapping. I spent the day sanding down my belly patch to as flat as possible, and preparing another whole lam for the inner half of the bow (mid limb to mid limb, through the handle). I'm hoping that'll sort out my issue of the outer limbs not bending enough, as well as support the hinge enough to prevent it getting any worse.

Glue is currently setting. I'll post a photo tomorrow when it's had enough time in the clamps.

[DC]

There comes a point where it's quicker, easier and better to make a new bow. I know there's a challenge to "make it work" but just sayin'

[Badger]

  I agree with you DC, if something is not right I just make a new bow. Just saving something that will fling an arrow is not worth the effort in my eyes.

[MattZA]

Oh I know it would be quicker to make another bow. I roughed out and floor tillered a long bow in about 45 minutes this week, and I'm sure you guys could do that in 10 (and undoubtedly much more elegantly and efficiently)

This is just me challenging the laws of physics. I have no real reason to succeed with this bow apart from principle. I don't hunt, I don't 3D hunt. Hell I barely even shoot at targets. I build and experiment with bows because it's damn good fun

To quote the excellent Tim Baker - "A Bow is Still a Bow Until it's Back Breaks".