Cutting Udon Ball
Pasta machine is better for rolling-out the Udon ball because the thickness becomes uniform. (Of course, you can roll-out the Udon ball using a rolling pin.) You cut the Udon ball into 3 pieces. You put corn starch on a choping block. The remaining flour is acceptable. In the case of the flour, the Udon dough is slightly gooey. So I like corn starch. You also put corn starch on the cross-section.
Rolling-out by Pasta Machine
You roll out the respective dough with a rolling pin little by little in every direction(like rectangle). Slow action without a strong force is recommended. The most thick setting of the pasta machine is recommended. You pur corn starch on the dough again. You put the dough on the pasta machine and rotate the handle. Slow action is also recommended at this time. If you rotate the handle too fast, the edge of the Udon dough would be broken.