Hello and welcome.
Did you type that intro on a phone? It is like the predictive text Gremlins have gone wild
The image of a 14 inch knife is hard to reconcile with something you would want to carry around your neck. Baldrick style, maybe, but that is different from neck carry.
Why would you want a sheath made of fat wood?
So that you always have wood to make fire with on your person? If your local woods have an abundance of fat wood, why would you go to the trouble of carrying a bit of it around with you?
If you are relying on the fat wood for an emergency, would you use all of it to get a fire going? At what point do you think you will have removed so much from the sheath that it no longer does its job of protecting you from your knife? I predict that if you have a sheath made of fat wood, and want a fire, you will usually have a little inner debate about whether the situation is really serious enough to use the sheath rather than look around your location a little more and find local supplies...and will invariably decide that bushcraft is about using the environment, not just carrying "bushcrafty" kit with you, and you will save the sheath for a "real" emergency.
The resin in fat wood will stop glue from working well, so you will have to lash the sheath together, primitive jungle style. Don't leave it in the sun, or the resin will leach out and make the surface sticky.
ATB
Chris