Shaft design critical constraints will affect the life of your generator and turbine shafts. When designing horizontal shafts, one will have many different considerations when replacing, upgrading or completing modifications, even if the original shaft has been in service for many decades. Critical constraints should not be taken lightly, ven small changes, such as adding a shoulder or sleeve, changing the location of a bearing, or modifying a radius. Alternate shaft alignments may also be required when completing the final design.