David, those blades are some of the most difficult blades in the world to sharpen – and ice drills must be very sharp to work properly.
Is there any problem with the edge on only 1 mm of the edge – the ice drill will not work at all.
Knifes have 1 dimension edges. Ice drills have 3 dimension edges – so – you must sharpen 3 different dimensions at the same time – and you cannot do that by freehand properly. You can succeed once if you are lucky. You probably will make the edge sharp – and in wrong angle – and that means that you cannot do it twice = you probably destroy the edge if you try to sharpen it by freehand.
That type of ice drill blades have been in use here in Scandinavia for decades and all people here say that they are impossible to sharpen.
I have constructed a sharpening tool that can sharpen them perfect – the tools name is IcePal. IcePal sharpens all 3 dimensions at the same time. Follow this link and study the photos there: http://edgepal.com/products-ice-se....
This type of ice drill blade are curved (screwed), concave shaped - and the sharpening angle are steep in one end of the edge and flat in the other end = the sharpening angle changes along the edge from steep to flat.
It is easy to get an edge with 1 dimension sharp. To sharpen 3 dimensions at the same time are very difficult. That is why this type of edge is one of the most difficult in the world to sharpen.
Study the photos of IcePal. The sharpening angle screw is 5 cm high on those pictures. The edge is mounted diagonal (important!) and IcePal use a convex diamond sharpener on 30 micron.
Things to remember. The edge must be 100% perfect – and NEVER try to sharpen the backside (downside) of the edge! If you do, you have destroyed the function and the ice drill cannot drill in ice no more. If you have burr on the downside, the ice drill do not function. If 1% of the edge is not perfect – it will not drill.
You must test the ice drill in ice after the sharpening, it is the only way to find out if you have sharpen it correct.