Some pencils will not sharpen with any sharpener that I have found. The worst culprits in my pencil box are those that are in the Hansa yellow family regardless of brand. So, here is what I do for those recalcitrant pencils. I use a single-sided razor and holding the pencil with the point end toward me and pointed down resting on the table  surface, I slowly rotate the pencil in my left hand (I'm right handed) while scraping the wood casing and pastel shaft in a downward motion. I can get a good point like this, but it requires going slowly and patiently or the pastel shaft will break. It's a last resort strategy for me as I prefer the sharpeners I reveiwed in a previous post.