Wednesday, August 19, 2015

MOTION STUDY VARIABLES - Frank B. Gilbreth - Part 6

CHAPTER IV -VARIABLES OF THE MOTION - Continued

NECESSITY

The necessity of the motion is such an important variable that an investigator is tempted at first glance to
divide all motions into necessary and unnecessary, and
to eliminate with one stroke those that appear to him
unnecessary. A more thorough investigation will be
apt to prove that no such summary elimination is
advisable.

A motion may be an unnecessary motion in a necessary
sequence, or it may be a necessary motion in a certain
sequence, but the whole sequence may be unnecessary or
inadvisable.

Example. In opening a paper bag of cement the aver-
age untrained laborer usually cuts the bag in two and re-
moves the paper in several pieces and with many motions.
The correct way is to cut the bottom with a shovel and
pull the bag upward in one piece by grasping the bag just
above the string.

This example shows both how motions may be unneces-
sary in themselves and how they may belong to a sequence
that is unnecessary.

The only final solution as to the necessity of a motion
will come when the trades are completely standardized.
It is impossible to determine whether or not a motion is
absolutely necessary until the method of doing the work
in which it is used is standard.

Examples. i. Motions which were relatively proved
necessary in laying brick by the " pick-and-dip " method
or " stringing-mortar " method, the brick being lifted from
the stock platform, became absolutely unnecessary when
the "packet-on-the-wall" method of handling brick was
adopted.

2. The same thing is true of motions eliminated by
handling mortar in a fountain trowel.

The final solution of the problem of necessity of motions
will be discussed later, though the subject is so large that
no amount of discussion could do more than touch it.

PATH

The determination of the path which will result in the
greatest economy of motion and the greatest increase of
output is a subject for the closest investigation and the
most scientific determination. Not until data are accumulated by trained observers can standard paths be
adopted. The laws underlying physics, physiology, and
psychology must be considered and followed. In the
meantime, merely applying the results of observation will
reduce motions and costs and increase output to an
amazing degree.

The path most desirable is usually that which permits
gravitation to assist in carrying the material to place.


Example. We have found that the most economical
height for laying brick is twenty-four inches above where
the bricklayer stands, while it is most economical to pick
the brick from a height about three feet above where the
bricklayer stands; that is, about one foot higher than the
top of the wall where the brick is to be laid.

The path is affected by the direction that the material
is to be shoved as it moves into its final resting place.

Examples. When the packet is placed on the wall it
should be placed so that the brick can be picked up and
moved in a comparatively straight line with the direction
that the brick will be shoved for filling a joint.

In theory the ideal path would be in a line of quickest
speed from the stock platform to the wall.

In practice it is seldom that the most economical path for
carrying a brick or mortar from the stock platform to the
wall is exactly a straight line from one to the other. It
will generally be most economical to move the brick in
the path that will bend the arms the least and that will
permit almost a swing from the shoulder.

PLAYING FOR POSITION

Each motion should be made so as to be most economically combined with the next motion, like the billiard player who plays for position.

The direction in which a motion is made may affect the
time required for a subsequent motion.

Example. In laying brick the motion of placing the
mortar for the end joint can be done quickest if it is done
in the direction of the next motion, such, for example, as
the next motion that puts the trowel in the position to
cut off the hanging mortar.

The sequence of motions in bricklaying, that determines
when the particular motion is to be made that puts the
mortar in the end joint, depends upon whether the "pick-
and-dip" or the " stringing-mortar " method is used.

When the motions are made in the correct sequence,
many of them can be combined so that two, and in some
cases three, motions can be made as one motion, in but
little more time than is required for one motion.

Example. Cutting off mortar, buttering the end of the
laid brick, and reaching for more mortar all as one motion,
in the " pick-and-dip " method.

SPEED

Usually, the faster the motions, the more output. There
are other advantages to speed of motions besides the fact
that they require less time. Speed increases momentum,
and this momentum may be utilized to do work.

Example. The momentum of the brick helps to shove
the mortar better into the joint.

Again, high outputs are generally the result of the
habit of speed in motions. Habits of speed are hard to
form, and they are hard to break.

Next to fewest motions, speed of motions is the most
important factor of high record of outputs.





The list of variables here given makes no claim to being
complete. The field of study is so immense that it is impossible as yet to give a complete and detailed method of
attack.

It will be noted in reading the discussion of the variables that it has been found extremely difficult to handle
each one separately. It is needless to tell the student, the
investigator, the cost-reducing manager, that, difficult as
the task is, for the best results each variable must be
studied alone. The effects of all variables but one must
be eliminated, or, better perhaps, all variables but one
must be maintained constant.

Quicker results may often be obtained by studying
several variables simultaneously, and for short jobs this
may be advisable. But for long jobs of repetitive work
there is no way so accurate and satisfactory as studying
one variable at a time. 

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