Shaft circumference=270×3.14=847.8

The length of one pitch spiral is √(847.8?+1200?)=1469.1

This size is Circumference of the round hole when blanking

∴Φ1=467.9≈468

Φ2=1730-27468=1928

Because the ring material is very It is difficult to make sure it is solid with the shaft, so the inner diameter can be 470 or even larger.

After cutting materials according to this size, the spiral connection seams can be guaranteed to be on the same bus line, and it is easy to shape because there is only twisting and deformation, no stretching, and no compression.