hardened steel / opening out a hole

[Dave Plowman (News)]

If you've got a cone cutter or easy way to enlarge the hole, B&Q do mild steel washers big enough for an inch shaft on a non critical device. ;-)

[Andy Dingley]

I've never been impressed with cone cutters. You need to clamp the workpiece _very_ firmly, and they still tend to make off centre holes.

For enlarging holes, a much better tool is a five-sided tapered reamer. For some weird geometrical reason, a five-sided cutter runs true. As it's not an unbalanced single-edge cutter, it cuts more evenly too.