How to sharpin a point post hole digger

[garry]

I recently purchased a used Husky 3 point post hole digger. It works fine in regular soil but I need to dig some holes in shale. I sharpened the point and that works very well. The cutting teeth just ride in top of the shale. I tried turning the cutting points upside down but that didn't help. so my question is how should I sharpen the the removable cutters. Should I sharpen at a certain angle? Should I sharpen the top side or the bottom side. Should I grind a relief behind the cutting edge? I seems line a waste to buy new points if I have a grinder, I just need to know where to grind. If anyone has a picture of new cutters I certainly would appreciate seeing them.

 

[bczoom]

If your cutting edge is worn off, it really can't dig in anything hard. It'll just ride on the center tip and your blades just ride in the air if the center tip is sitting on something hard (like shale).

I'd look at google images for cutter blades similar to yours. If yours don't have the same shape, you could grind to make them look similar. If yours don't have the same length from attachment point to cutting edge, it's probably time to replace. I think they're only $20-30 for a set.

Another thing I've done with half-way decent success is to put a 2x4 or similar as a lever on top of the gear box, wedged between it and the 3-point top link arm. Have someone on the other end of the 2x4 and have them push downwards on it while you're digging. That'll exert a decent amount of extra down force which helps it dig better.