Yesterday I case hardened the replacement setting bar slide (sorry no photo), using the method and recipe in the excellent Clickspring video...
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I heated the clay package in the furnace till it started glowing, and then another half hour, so I hope there is a deep enough skin of Martensite to still have a hard surface after surface grinding from the current 6.18mm down to the final 5.78mm dimension.
Ground another lathe bit. This is so easy, I can see all my lathe bits haveing defined radius's soon.