The fractional horsepower electric motor business is extremely competitive, and a new idea can give a company an advantage in the marketplace. Litton/Clifton Precision (Murphy, NC), a manufacturer of small electric mo-tors, utilizes a brush holder assembly. For years, the company has used high-impact, high dielectric molded brush holders, manufactured by Phoenix Electric Manufacturing Co. (Chicago) and has mounted them in its motor housings with tolerance rings from USA Tolerance Rings (West Trenton, NJ). Tolerance rings are highly engineered, corrugated steel fasteners used to economically join mating cylindrical parts. The corrugations deflect and allow the tolerance ring to act like an elastic shim.

Many companies have turned to tolerance rings after years of struggling with the mess and cure time of epoxy or the uncertainty of a setscrew. The tolerance ring allows for one-step assembly that retains the brush holder in its axial and radial position, and extends the motor's brush life.

For many of its motors, the company uses the traditional assembly method, which involves a BN-style ring, whose ends overlap in the free state. The ends of the ring are pulled apart and placed over the brush holder body, allowing for a small gap be-tween the ring's end. The ring is pushed axially until it rests against the brush holder's shoulder. The entire brush holder assembly is then inverted and pressed into the hole in the motor OD.

For one of its new motor designs, the company has opted to use a different type of tolerance ring, which allows it to use a brush holder that is molded without a shoulder. The AN-style ring has a free state gap. The ends of the ring are brought together, placed in the bore and then moved axially until it rests against a shoulder. The brush holder is then inserted to the desired depth. This new design may offer some advantages in terms of cost savings, as well as ease of assembly, without any decrease in brush life.

For more information on tolerance rings, call USA Tolerance Rings at 877-865-7464, visit or Reply 6.