If you want a psk sized sharpener use sand paper. 600 to 1000 grit wet or dry (the black sand paper) does a decent job on most edges. It is not as durable as other sharpeners but it is cheap and disposable. Just place the paper on a flat surface and use it like a stone. It might even work well placed on the topside of your tin with carpet tape, although i haven't tried it for that application. I have used it taped to glass for sharpening and decking edges on chisels and plane irons.