if the wall were only .25-in thick?
The effect of a thinner wall is dramatic. The shaft with the .25-in wall can carry less than 20 percent of the torque of the shaft with .5-in wall.
Conclusion
Engineers tend to design using an ample safety factor, and older equipment in particular was over-designed even by today's standards. Of course, that is one reason many of us appreciate older machinery; it was darned reliable!
Keep in mind that adding a keyway to an existing shaft weakens the shaft. Likewise, increasing the bore diameter of a hollow-shaft reduces the torque capacity. Consider modifying a shaft only with good engineering support. Even then, remember that the greater the consequence of failure, the more generous the safety factor should be. After all, who wants to board an elevator that was designed and built with no safety factor?
