There are a few of us old timers still around who would say that straight edge or string alignment is good enough. At that time and for certain applications that was actually good enough. Now we have state of the art tools that we can use to get us a near perfect shaft alignment. But do I need near perfect? What will that extra bit of time get me and is it worth the time?
We cannot argue that proper coupling/shaft alignment increases the life of all of the components in the drive train. Misalignment in connected driven equipment causes a host of problems that will affect and shorten the life of all rotating components in the system. Misalignment affects many things like: vibration, bearing temperature, noise, bearing wear and coupling wear. All of these affected components will have their runtime life shortened dramatically and this will result in added costs for replacing failed parts, inventory cost due to stock spare parts and lost production times.
There are three types of misalignment: angular misalignment, parallel misalignment, and a combination of both. Angular misalignment occurs when the motor is placed at an angle to the driven equipment. Imagine if centerlines of each piece of equipment were extended, would they cross each other or continue on the same center line. If they cross, this is angular misalignment. Parallel misalignment happens as a result of two shaft centerlines both being parallel, but not on the same centerline.
Combination misalignment is the result of both angular and parallel misalignment. Today there are several alignment tools available. These tools range from straight edges and feeler gauges, to dial indicators, to laser optic devises. All of these methods still have their place in industry today especially on some specialty piece of equipment that will only allow for a specific tool due to it's setup.
So, getting back to the question above: What will that extra bit of time get me and is it worth the time? I think that we will all agree that proper alignment is definitely worth the time and the added effort.