Strived for a couple of seasons, and got frustrated, while trying get my edges properly tuned. Finally got it dialed in following instructions given by a pro in a tuning demo arranged by a local alpine race shop. Key element for success was to buy a good file, probably the best currently for this purpose: Viiala Finn File cut 1 (not anymore made in Finland but in Portugal, available at least through Vola and Wintersteiger). Earlier I have used those by Icecut (Vallorbe) and Öberg (Bahco/Sandvik) but Viiala is totally on another level. Warmly recommended, probably the best ten bucks one can use for maintenance tools. The only drawback is that for slalom skis one has to cut the file into two with a grinder and thus some extra work to do.
Another useful hint was the use of brake pad cleaner spray for removing metal debris from files+diamonds.
Enjoy tuning without hassle, all the best, jaakko