Not sure what FOG is but this one has more info and better pics.
Planer knife sharpening jig - DIYWiki
There are hundreds of others on line too as all you really want is something to hold the blades at the right angle. While on angles its best to go a degree or two higher than the bevel so as make a micro bevel. that means you can sharpen them a lot faster as there is less metal to rub away. I was about a degree the wrong way so the first sharpen took ages.
Regards
John