On the cold saw or using a hacksaw cut off the head of the bolt.
Step 2: Face the cut flat on the lathe on both sides
Face the two pieces so they are perfectly flat and will mate together well later.
Step 3: Drill the appropriate size hole for your tap in the base piece
Drill a hole in the base section of the bolt. This is where the logbook will be so make this large enough.
Step 4: Using a slightly larger drill bit widen the hole at top
If your threads go all the way to the head of the bolt you can skip this step, otherwise you need to make a small area slightly large to accommodate the threaded section of the head piece that does not have threads.
Step 5: Cut the head piece on the lathe to the correct diameter for your threads
Verify the diameter required by your tap and tie set and cut the head piece to the correct diameter for your chosen threads.