Ironbark mollegabet from downunder

[Hamish]

That is a lot of weight to drop, with no apparent cause. Has it taken a lot more set than in the previous unstrung photos?
Are there any chrysals/compression fractures near the hinge(and or localized set). Moisture can cause a drop in weight, increase in set, but 17lbs is a heck of a big drop.

A pair of outside calipers can go a long way in helping to prevent a hinge. Checking the thickness taper whilst tillering makes sure you will pick up any thin spot before it's too late.

I have made stave bows from grey ironbark, sapwood limbs and heartwood on the handle, and also bamboo backed bows from heartwood. It usually makes a good bow, but sometimes frets even when the tiller is good.

[willie]

Would high humidity cause such dramatic weight loss? It's been drizzly weather here the last few days.

all of what Hamish mentioned above and I quess one other thing to suspect is if you you might have been making adjustments too quickly and without letting the adjustments settle in before further tweaking.  Working slowly as you approach full tiller is prudent.

Some folks like to shoot the bow at reduced draw lengths before drawing it out further. A couple of times.

I know I can see one thing at the end of a tillering session,  and see the limbs bend in a different way when I string it up again tomorrow.