The Tormek SVH-320 Planer Blade Attachment sharpens HSS planer blades of any length, and miter trimmer blades, straight along their whole edge.
You set the depth, and the jig guides the blade so it's ground straight to that depth every time. Blades longer than 270 mm (10-5/8 in) are moved along and sharpened in two steps. It works on the T-4 and older models, but Tormek recommends the T-8.
Engineer Torgny Jansson founded Tormek in 1973 to build a modern version of the old Swedish water-cooled grindstone. The name is short for Torgny's Mekaniska, and the very first model was driven by an electric hand drill. Tormek is based in Lindesberg, Sweden, where all of its product development, engineering and production still take place.