The procedure for aligning two rotating machines requires measuring their relative shaft positions and adjusting one or both machines. Until recently, though, how closely the shafts need to be aligned was an open question. That changed with the publication of American National Standards Institute/Acoustical Society of America (ANSI/ASA) standard 2.75-17.

This 94-page handbook (3.5" x 6", 9cm x 15cm) contains carefully selected materials designed to assist repair firms in their everyday work. Just as important, your customers and potential customers can use this pocket handbook as a handy reference for mechanical data for motors and driven equipment.

Two case histories point out the need for caution when working with metal sprayed shafts:

• Example 1: When measuring the bearing fit shaft size, the micrometer didn’t feel right; mushy, not solid, although the journal was very close to the specified size. After using two micrometers to experiment with one of these frosted fits, it was discovered that the measurement on one micrometer changed when tightening down the other micrometer and vice versa.
• Example 2: The bearing journals on a large armature began to fail while the armature was coming up to speed in balance stand.

The paper "Steel—Metallurgy and Practical Application of Various Grades of Steel" by Gene Vogel, presented at the EASA Convention 2016, provides an in-depth exploration of steel alloys, their composition, processing, and applications, particularly in the context of machinery repairs and replacement shafts. Vogel emphasizes the importance of selecting the appropriate type or grade of steel for specific applications, drawing on both practical application information and technical metallurgy theory.

“What’s the proper clearance between a shaft and the sleeve bearing it rides in?” Chances are each of us has a rule of thumb for this, probably related to shaft diameter.

This technical paper, presented at the 2014 EASA Convention, will help you understand how and why shafts and fasteners fail.

When a shaft is in need of repair, often the frst step is to determine the corrective method required. Economics and best practices are typically significant factors in the decision-making process in selecting the method of repair. The types of shaft repairs that will be dealt with here are: opposite drive end bearing journal, drive end bearing journal and bent shaft. The objective is not to detail the repair processes, but to identify the most common methods appropriate to the types of repair and considerations associated with each method.

Like most maintenance and repair tasks, a successful outcome is generally predicated on good planning and preparation. The first steps in the process are often the most critical.

Have you ever wondered why the shaft of an electric motor is often larger than that of the driven equipment? One reason for this is that the standard shaft sizes specified for the standard NEMA frame machines are larger than the minimum required, as we will see in the examples herein. Manufacturers tend to design using an ample safety factor. Given the dire consequences if a shaft breaks, that is understandable. Even so, the difference between a T and TS shaft can raise questions for those unfamiliar with mechanical design. It is important that the shaft is large enough to (a) transmit the required torque without exceeding the maximum allowable torsional shearing stress for the shaft material, and (b) prevent torsional deflection, or twisting, during service. All this, with a substantial safety factor.

There are a number of ways that the shaft of an electric motor can become magnetized in service. The most likely culprit is electric current through the motor and shaft, either from internal dissymmetry, welding or from a variable frequency drive. It can also be caused by electrical faults in the system, or even a lightning strike. If enough current does pass through the shaft, then it can remain magnetized, even after it is taken off line. The problem is that when a shaft is magnetized, it can further lead to bearing failures, unless something is done to eliminate the residual magnetism. The first reason for bearing failures is that the residual magnetism can cause shaft currents, which can quickly lead to bearing failures. But in addition, a magnetized shaft will attract bits of metal to the bearings. This reduces bearing life because it damages the bearing surfaces.