I have a flywheel that has been blanchard ground that I need to redrill for a 10 1/2 inch clutch. My machinist called me and said that the area where he has to drill and tap falls into the ground surface. He is concerned that this area may be too hard to drill and then tap. Anyone have any experience with this that can offer some suggestions as to his concerns.
Blanchard grinding is a process to remove material to achieve a flat surface. https://www.bourn-koch.com/what-is-blanchard-grinding/ It normally doesn't work harden the material. Drilling and tapping should not be affected by a flat surface, and a small chamfer should remove any material at the edge of the hole brought up by machining. If he has a rockwell checking machine, he can check the hardness of the part. https://en.wikipedia.org/wiki/Rockwell_hardness_test There may be other concerns, like the bolt pattern not aligning with any ribs in the back side, material thickness at the pattern or being able to ensure a concentric pattern? I have found that arguing with a professional about their craft is often futile. Don't expect to go to a diner and tell the cook how to fry eggs.
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