Machine tool estimating / by Randolph A. Harding

MACHINE TOOL SSTIMATTNG

by Randolph A. Harding, Jr.

Machine Tool Estimating

"/hat does the lad of twelve want to be when he grows up? A
soldier, a sailor, a doctor, or maybe an engineer. But how many
children get a chance to carry out their dreams? They dream of
being great men of which there are few. There are many many jobs
that the average person never hears about. 'Never reads about
them in books or sees them in the movies. I worked at such a job
I'or approximately two years. Upon meeting some old friend, he
would say, "What are you doing for a living?' 1 "Estimating", I
would say. Then I would have to go through an explanation. In
fact, I became quite used to explaining this job. Do you know
what an estimator in a machine shop would do? In the following
paragraphs, I would like to introduce his job to you.

In this paper the term "estimating" is used to cover the
planning of a proper method of doing a machine job, and the
figuring of the time required to produce a piece. The term
"estimating" is used because we are talking about the planning
of a job which is to be produced, rather than the time study of
a job that is already in production.

It is entirely possible to estimate machine work with a
reasonable degree of accuracy before the job is put on a machine.
In ortier to determine the proper set-up, and to provide the prop-
er tooling it is very important that at least some of the steps
required in estimating are taken on every job, either by the
operator or by the tool engineering department.

There are seven principal steps to be taken in making an

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estimate on any machine work, as follows:

1. Study a blueprint of the job, and if possible, a sample
of the work; study the preceding and following operations
and the quanity to be made.

2. Select the proper size and type of machines that are
available .

3. Determine the holding method.

4. Outline all necessary operations.

5. Determine multiple and combined cuts.

6. Determine speeds and feeds.

7. Figure the actual time required to produce the piece.
It is always necessary to study the requirments of a job

before the proper tooling method can be determined. In doing
this it is necessary to know the limits of accuracy, and the
finish required. A careful study of the joo will bring out many
other points that affect the tooling and the speeds and feeds to
be used. The quanity will also determine the set-up time allow-
able .

The estimator will have to select the machines upon which
the job can be done. In most cases he will have to work with the
machines that are already available. On the other hand, if a
new job is to be produced in large quanities and new machinery is
to be purchased, then the estimator is not limited to his own
shop*

Sot only must the estimator determine the best method of
holding the piece so that proper speeds and feeds can be used,
but he must also determine how elaborate the holding device
should be. A very important element in making this decision is

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the number of pieces to be produced, and the estimator should
carefully figure not only a method of holaing the work that vail
be satisfactory, but also one which is justified on a cost
analysis has is.

The fourth item - the outlining of all operations- means
the actual listing of all cuts to be taken, and this quite
naturally raises many questions as to how the cuts should be
taken; whether the holes should be bored or reamed; the number
of cuts required to produce the required accuracy and finish;
whether forming tools or plain cutters are most economical, etc.

Multiple or combined cuts? This depends upon the machine
used and the piece. The more cuts we can take at one time, the
cheaper the piece.

Determining the speeds and feeds is important, but not a
very difficult matter after the pro ceding steps have been taken.
Tables have "been made that show the various normal speeds and
feeds for various materials. The estimator should also determine
the type of cutting tool to be used. He may use high speed steel,
stellite, or carbide cutters. The selection of these cutting
tools would depend partly upon the machine being used, but if
the machines are modern, he does not need to hesitate to use the
best cutters when they will allow the use of heavier feeds or
higher speeds.

After selecting the machine, determining the method of hold-
ing the piece, listing the operations, and determining the cuts,
and types of cutters and the speeds and feeds to be used, there
is still the job of figuring the actual time required to produce
a piece. To assist the estimator, charts have been made which

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show the time required, of one inch of cut at each speed and feed
on the machine. By applying this factor to the length of cut re-
quired, and a ding the machine and work-handling time, the actual
time required to produce the work results.

The estimator's work is finished. With the estimated time
as a base, the cost of a job still in the blueprint stage is
determined. A good estimator must know everything: from engineer-
ing to the simplest operation in the shop.

Bibliography

Turret Lathe Operator's Man ua l , 1940, by Bailey and Longs ire et

Shop Theory , Henry Ford Trade School.

Machine Tool Operation , by Henry D. Burghardt.

Oral ; - Production Dept, Balmar Corp., Baltimore, Maryland.