When Lars and I first started carving ice, we underestimated the value of some of the more traditional ice carving tools. Chainsaws would be essential, we knew, but we didn't figure that chisels would be so important to the mechanical ice sculptor as they are to the traditional ice sculptor. We only had a few, small, one-handed chisels on hand that first year, but wasn't long before we realized that we needed more chisels, sharper chisels, bigger chisels, and better chisels.
We found that professional ice carving chisels are rather expensive, so we tried making some of our own or refurbishing antiques found on eBay. These efforts weren't terribly successful until one day a couple years ago when Lars found a nice, large, 3/8 inch thick piece of tool steel. He cut it up into several chisel blades (up to 4 inches wide) and welded on sockets for hockey stick handles. These chisels have been an outstanding addition to our arsenal.
When they were new, Lars had them professionally sharpened. They cut ice much better than any chisel we had used before, but some of them lost their edges fairly quickly. After learning a thing or two about sharpening chisels I came to realize that the reason some of them were better than others was that they had flatter backs. The professional sharpener had done a terrific job on the bezels but hadn't flattened the backs. Since the cutting edge is the intersection of two planes, the bezel and the back, it is important that both be very flat. Over time, I've tried to flatten the backs of these chisels, but it is a great deal of work. Last year I took a particularly troublesome one home with me, and I have been trying to flatten it this week, starting with a belt sander and moving up to a coarse diamond stone.