Solving a Power Screw Question - Get Help Here

[Saladsamurai]

I was reading through some examples in my Design text when I came across this one.

This was their solution:

I am not sure that I completely follow it. Can someone help shed some light on what's going on here?

I am assuming that the specimen to be put under tension goes where the "B" dimension is right?

 

[nvn]

Yes, the tensile specimen goes where the B dimension is. Both screws must have the same hand. My impression is, their explanation is very poorly written. Here is the answer I arrived at before reading their solution. The machine is missing thrust bearings at the top of the screws. Therefore, the machine should not be used for a compression test, because galling of the upper channel web material might occur. Plus, the diagram shows only a small-diameter shank inside the upper channel.