I started with a 3" pole did some splittin and got a plank about 1/4 thick of a inch by 1/1/4" then cut to shape the 2 parts, after that I cut notches so the 2 parts slide into each other, glued ,shaped, cut thumb, sanded sealed, shot 
We need more information on that 'cut thumb' stage... I've done 'rasp thumb' but I'm not sure if that's ok instead?

Del