100% of the traditional technological formula of pure tartary buckwheat vermicelli

100%, which is basically impossible because it is fragile and easily broken. You should add some flour anyway. If you have to try, you can try to boil 1/3 pure buckwheat flour and dough in a boiling pot (this step is to make the flour sticky), then add other buckwheat flour and dough and try processing. I don't think this is a good idea. Another way is to add some boiled cassava flour.