The problem was the tool advance mechanism.
Beorn had four versions crossed out in the margin now. The latest was a lever system weighted at the far end to push the cutting tool forward with a constant force. He understood at once why it would fail.
Iron was not uniform through a casting. The softer sections would let the tool run faster, the harder sections would slow it down, and the bore would follow the casting flaws instead of its true center. The result would be wrong in a new way. Possibly worse, because at least the current flaw was predictable.
He drew a diagonal line through it.
His hand kept moving, and now it was sketching the separate condenser chamber for the V3 engine design instead of another attempt at the advance mechanism. He noticed the change and looked down at the page.
