From what I have read in the TBB3 it sounds like steaming reflex will actually weaken the wood? Is this true for dry heat aswell?
no on both counts.
After steam bending you need to let the wood dry back out because of the moisture you have added to the steamed area.
...and when you use dry heat you have to let it rehydrate. If you use dry heat to temper to the belly, you've actually INCREASED the compression strength of the belly wood.
So on this line of thought if you used steam to bend a bow into reflex and then used heat to set the belly while it was a little wet what would happen? Hickory is what I am refering to since it is steam bent most offen and tempering the belly is a good idea.
If the wood absorbed enough moisture during the steaming the dry heat will force it out and it done too quickly it can cause checking. If you can seal the wood from taking on moisture you can prevent the checking. Shellac is the only thing I know of that can take the moisture and heat of the steam and still seal the wood.
You can add reflex and temper the belly with dry heat alone and at the smae time. With some of my selfbows this is the final step before final tillering, sanding and finishing.
Hickory is a bit finicky about moisture and stress so it is important to let the wood rehydrate slowly or it will crack or check. You cannot force it to rehydrate or dry to quickly accordingly. Just let Hickory dry or hydrate on it's own. Check it by weighing it.