I made a large diameter gauge (as shown). When rounding, first fix the fixed amount of claws 6 at the zero point, adjust the movable amount of melon 5 to the required radius, tighten the fastening screw 4, then handle the handle 1 with the left hand, place the fixed amount of claws 6 in the punching hole, and shake the right hand. The handle 1 rotates the movable claw 5 to be rounded.
Large diameter gauge