Bananas turn brown, avocados turn mushy, cars rust. Those are things we recognize as having a shelf-life. They are not permanent. They are perishable.
When discussing steel shafting, especially in the field of maintenance, straightness is an important property. If a shaft is received at the end user’s plant bent, It is not usable. You can’t grind it. You can’t machine it. You can’t install it. In fact, unless you are cutting it into little stubs for pins, or whatever, it is pretty much useless.
So, although we can all agree that straightness is important. We must understand that even if the bar has been straightened, it will not necessarily remain straightened. Straightening, and the subsequent handling, of a steel shaft is a commitment. Think of high school kids being required to carry a raw egg around for several months without breaking it. The exercise is intended to teach responsibility. It is designed to instill a sense of appreciation of the delicate nature of that item in your care.
We should think in terms of that when discussing anything about bar straightness.
Even if you require, or purchase “Pump Shaft” straightness, or, “Pump Shaft Quality (PSQ), responsibility does not end there. From the moment that product was created it began deteriorating. The severity of the deterioration will be relative to many influences. But, probably the most influential of all will be the diameter relative to the length.
A PSQ bar of 4140 Heat Treated alloy that is 3-1/2″ Dia. x 4 ft. long will be much more likely to maintain its straightened condition than will a 1-1/2″ Dia. shaft that is 16 ft. long. Then there is movement around the plant, packaging, shipping, unloading, machining, fabrication, installation, etc. It’s like those little turtles heading for the ocean once they’ve hatched. It’s a wonder any of them actually make it to adulthood.
The point is, if you are judicious, you should be able to solve most shaft problems where straightness is the rub. But know that it is not a slam dunk, just because the invoice says “PSQ”.
-Howard Thomas, May 17th 2018