Take-down Bamboo backed ipe trilam recurve - Compression fracture... ideas?

[Tommy D]

It’s been a while since I checked in - but could really use some advise on this one!

This is an ipe cored, ipe belly (but from clearly very different “ipe” as the belly wood is very dark and greenish and the core is a lighter coloured “ipe”)....

I glued in some deflex first. Then curfed the tips and pulled it into a reflex-deflex shape with a bamboo backing.

There was too much deflex and too little reflex for what I wanted, so I cut it in half and glued it into some take down sleeves.

It was all going pretty well ... it’s 62 inches nock to nock when strung and pulls 55lb at 24inches so far. Was aiming for 28” at 55lb .... but I’ve noticed what I think is a crysal on the lower limb.   

Lower limb is a little stiffer than top limb - I think - but some of this is also an optical illusion at brace height because the top limb is a slightly different shape than bottom limb.

Anyways....

Was wondering what my options were... photos attached below. What I think is a Crystal is under the x in the white circle in third photo...

1) keep going and don’t touch the crysalled area

2) keep going but bring poundage way down

3) cut out a plug from the belly lam area and glue in a new piece of ipe onto the Center core

4) make a new bottom limb

5) go back to making normal R/D bows 

Here are some photos!

I can send one at 24 inches draw tomorrow. Dark and cold outside right now!!

[RyanY]

The shape doesn’t look too extreme. Where is the compression fracture along the limb? I’m not certain but the unbraced and braced shape of the reflexed portion look very similar so they may not be working enough causing the inner limb to be stressed. Given that it failed in compression you’d have to retiller the whole bow at the same draw length while lowering the poundage to prevent stressing that area even more.

[Hamish]

I would continue tillering, but wouldn't touch the chrysalled area. Run some calipers over the area to see if there is an obvious weak spot where the chrysal is.

Mark out the length of the chrysals with pen, to see if the chrysal get bigger, as you increase the draw.

If it starts getting worse, stop and patch. Use a long patch much bigger than the immediate area, rather than a small patch(small patches tend to fail more from my experience). Use a rigid glue like urea formaldehyde, the glue line is much harder. Most other glues will start to lift.

Even if I got to target draw weight/draw length and the bow looks otherwise okay, I would still put in a patch.

[bownarra]

Once ipe crysals you are done.....
Seeing as it is a takedown, personally, i'd make a new limb.
A picture of it drawn would help. I think the same as Ryan. Inner is working too hrad. Your reflex is over too short a distance. Once you have a bend like that in the outer limb it will be way hard to get it working properly. The 'trick' with reflex/deflex layout is to make certain that the delfex is only in the inner third and the transistion to reflex is very gradual, increasing in reflex as you move towards the tips.
Normally people try bending parallel lams into a r.d shape, you can....but it is much easier if you bend pretapered lams...they will actually want to do what you want them to do Parallel lams tend to give an incorrect shape that is a nightmare to tiller
If I remember correctly you are in the UK somewhere? If so contact me and i'll grind some tapered lams for you.

[Marc St Louis]

There are actually several chrysals there. 

My experiences with Ipe is that there are 2 types.  One that produces dust with a yellowish tint to it and one that produces dust with a reddish tint.  Yellow is better

[Tommy D]

Mark - thanks - I think I have both; belly wood is the one with a greenish tinge. Core is the red one.

Bownarra - I sent you a PM - and many thanks for the kind offer. Would love to discuss bows in person one of these days!

The chrysals are in the beginning of the outer third of the limb. I am tempted to try a plug for now. I can glue up another limb later. It is the nice thing about these take down sleeves.

Will post a picture in a bit