Electric Motors
(Tuners' Journal - April 1928)

By Wilberton Gould, Member N. A. of P. T., New York City

Service, as defined by Webster: "An act of one who serves."

It is one of God's greatest gifts to mankind, for who is happy who does not serve? Hence it follows that service requires sacrifice. It is the foundation stone of every enterprise. Whatever it may be, its success or failure depends upon whole-hearted co-operation.

And may service and sacrifice continue to be the keynote of our progressive Association.—The Author.


In the electrically driven grand or upright piano the function of the electric motor is to transmit power in an even and constant manner to the pump through the medium of a belt. In order that the maximum of power may be delivered by the motor to the pump it is necessary that the electric unit be of sufficient size, that it be constructed of the best materials and properly mounted, that it be free from operating defects and be silent in operation.

It is extremely important to keep the oil or grease channels of the bearings free from congealed oil or grease. Otherwise, the lubricant will not reach the point of rotation, and friction will occur, with the added danger of burning out one or more bearings of the motor. This will result in a ruined motor, and is also likely to cause a fire within the instrument itself, particularly in the grand type of piano.

In the grease cup type of lubrication it is wise to remove the entire cup and clean out the inside of the cup and the feed channel, and at the same time make sure that there is no congealed grease in the opening where the grease cup is screwed on to the bearing. In the oil cup type of the older designs the same procedure should be followed. In the later type of the centrifugal oiling system little or no trouble will be had, except in cases of extreme friction, which will be treated later in this article.

For the efficient operation of the electric motor it is of the greatest importance that the lubricating system of the motor operate properly. It should be inspected not less than four times a year, or at every service call. "An ounce of prevention is worth a pound of cure" is extremely applicable in this connection.


In the modern electrically driven piano manufactured today there are two types of motor used, that is, direct and alternating, using a line voltage of 110, 220, 230 and 250 volts on either direct or alternating, and in the alternating type there are 25, 40 and 60 cycles.

In connecting a new set-up or installation in an owner's home make sure that the motor is of the correct type and voltage before attempting to turn on the electric current. Also bear in mind that it is highly desirable to have a separate feed circuit for the motor direct from the main supply circuit of the home. In many homes there are numerous lamps, and so forth, connected to the baseboard outlets, and very often the load demand on the circuit is greater than was intended when the wiring was installed. Therefore, when the motor is operating there is likely to be a drop in the line voltage, which will impair efficient operation. A few comments will be made in this article on overloading the supply line, on the danger of fire at some weak point in the supply line and on heating the motor, and these should be remembered as safeguards for the piano owner and protection to the tuner.

Avoid splicing the supply cable to the motor with a type of wire different from the regular equipment supplied with the piano. The supply line from the outlet to the motor should be as short as consistent, in order to avoid line loss in voltage. When splicing electric wires make a good, solid joint, properly soldered and taped. In case of a sudden heavy demand of current a poor joint will cause trouble.

The modern electric motor is supplied with a brass or nickel-plated plate screwed on the shell, which gives the type, speed and rating of the motor. This should be consulted before the current is turned on. If you have any doubt as to the kind and voltage of the current supplied, call the electric light company.


The driving pulley of the motor travels in a clockwise direction (to the right), or in a counter-clockwise direction (to the left), but in nearly every case the direction of the rotation of the pump is plainly marked by an arrow on the plate on the pump. Should the motor not operate in the proper direction it is a simple matter to change its direction, as follows:

On the direct current type remove the supply leads from the brush contacts, interchange to the two remaining leads that come from within the shell of the motor and connect the supply leads. On the alternating type follow the same procedure, only make the interchange at the terminal points.

The motor should be in a direct line with the pump and suspended evenly, so that the belt will travel true in relation to the driving pulley of the motor and the wheel of the pump. If the pulley and the wheel are not in line there is danger that the belt rim will cut and ruin the belt in a very short time.

The belt on the driving pulley of the motor should be just tight enough to turn the pump wheel on a full load without slipping. If it is not, friction will result and will cause the pulley to heat up, and in turn the shaft, and if neglected, the bearings, which, consuming the lubricant too quickly, will cause the metal in the bearings to become so hot that they will "seize" on the shaft, the motor will stop, and is apt to burn out. Suitable means are provided on the motor frame to take care of the stretch in the belt. Where the belt has run a long time and the motor has been moved up to its limit of travel to compensate for slack in the belt against the mounting frame, the belt should be replaced with a new one. Otherwise, two things will happen: the motor will become noisy and it will heat up because the belt is slipping on the motor pulley, with the results as stated above.

Herewith are a few rules for determining the length of belt required for belt-driven pumps :

Move the motor to within one-half inch of its travel toward the pump, just so it does not touch the motor support frame, and proceed as follows:

(a) Add together the diameter of the pulley and the pump wheel, divide the sum by 2, multiply the quotient by 3-1/4 and add the product to twice the distance between the centers of the motor shaft and the pump shaft. The sum will be the length desired. Or

(b) Add the diameter of the pulley and the pump wheel, multiply by 3-1/8, divide the product by 2, add the quotient to twice the distance between the two shafts. The result will be the desired length.

Always carry a spare belt in your bag if possible.


In mechanics, friction is defined as follows:

By Rankine:

That force which acts between two bodies at their surfaces of contact so far as to resist their sliding on each other, and which depends on the force with which the bodies are pressed together.

By Morin:

(1) The friction between two bodies is directly proportional to the pressure, that is, the coefficient is constant for all pressures. (2) The coefficient and amount of friction, pressure being the same, is independent of the areas in contact. (3) The coefficient of friction is independent of velocity, although static friction (friction at rest) is greater than the friction of motion, and the act of rubbing the surface of one body against that of another; the effect of rubbing or the resistance which a moving body meets with from the surface on which it moves.

From the foregoing definitions it will be seen why the belt on the pump should not run slack. If the belt is at its proper tension the electric motor will run quietly and be cool.

There is a right and a wrong way to put on a belt on any piece of mechanism. A sewed or spliced belt should be put on with the splice running in the same direction as the rotation.


The prime cause of noise in an electric motor, nine cases out of ten, is neglect of proper service. Many service men are prone to leave the motor alone. The following are some of the simple rules whose application are so necessary to the efficient operation of the motor:

1. Keep oil or grease channels free and clean for lubrication.

2. Keep oil or grease cups supplied with lubricant.

3. Keep the motor free from excessive dirt and dust.

4. In the direct current type, keep the commutator and contact brushes clean at all times.

5. In the alternating type, keep the centrifugal switch springs free, and see that the guide screws are not too tight in the guide slots. Keep the contact points on the shaft and on the centrifugal switch clean.

Any of the following conditions will cause an electric motor to become noisy in operation :

1. Improper mounting on the motor frame.

2. Compression and hardening of the felt.

3. Too high or too low line voltage.

4. Lack of lubricant reaching the bearings.

5. A dirty commutator which will cause the brushes to miss contact.

6. Brushes not riding evenly on the commutator.

7. Worn bearings, which will cause the shaft to shimmy while the motor is running.

8. The motor shell coming in contact with the posts of the piano or the frame.

9. An overload on the motor, because of high pressure on the pump or tight bearings.

The writer recommends very strongly the booklet by The Holtzer-Cabot Electric Company, 125 Armory St., Roxbury, Boston, Mass., on the care of special noiseless piano motors. It is very complete, it applies equally well to any type of motor, and should be in the hands of every tuner who services any type of electrically driven piano. It will be forwarded upon request.

The subject of the next installment will be Electric Expression Players.

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