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Full text of "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.