Thanks everyone
It could be a trick of the light, but those edges don't look sharp at all. A sharp edge doesn't have a line of light reflecting off it.
well they're not razor sharp like a knife but I didn't want to take too much off till I knew what I was doing
is there an existing bevel on the horizontal cutters? it looks like you've sharpened the bottom of them when there's usually a bevel on the top
No bevel on the bottom, it just follows the natural curve. It looks that way because I just took a small amount off to remove the surface rust but didn't carry it on very far. Most of what I took off (and that wasn't much) was on the inside.
Don't quote me on it but... that looks like a version of a gedge or scotch pattern auger, which are designed for rough work or end grain. The upward pointing wings are designed to slice off splinters rather than prevent them (not that downward wings do a great job of it every time btw ) but need to be sharpened on the inside face and the main cutting edges are sharpened as per the video I linked to before.
I just did quote you didn't I?
Thanks for the info I'll see what Mr Google has to say about Gedge. Ah I found this link.
http://www.theluddite.com/auger_bits.html
The gedge pattern (first in the link picture) has curved over cutters and is mainly for end grain but mine isn't that pattern, it looks like the second to last described as a Scotch pattern. So it seems it's meant for rough work on hardwood and probably never gives a particularly clean entry hole. I think I need to do a bit more sharpening on the inside edges and see how that goes.