Not intending to seem sarcastic but you can more helical than you need. I use a Bitzenberger and set a shaft in the jig then place the clamp on the shaft, set the helical and file the aluminum clamp down to where it contacts the shaft evenly along the clamp's contact length. Take your time and "eyeball" often, it can be done in 15 or 20 minutes. I use a 10" half round bastard file and it helps to shine a light behind the clamp when you place it on the shaft occasionally to check your progress as you file it down.