Dremel has a very handy attachment for blade sharpening. I upgraded the burr to a diamond stone. One really should sharpen after every couple of tanks. This tool makes it easy to keep sharp and maintain the proper angle.
Dremel A679-02 Attachment Kit for Sharpening Outdoor Gardening Tools - Power Grinder Accessories - Amazon.com
By the way I have a 35 year old Stihl. Still works great.