TITLE: THE BEST WAY OF TEACHING FIRST LEARNERS ABOUT DRILLING MACHINE (THE MACHINE TOOL)
BY: OKWANY AMOS.
M.Sc. (Mechanical- Machine Building Technology)
Dip. (Project Planning and Management)
Cert. (Teaching)
Cert(s): (General: Higher Dip Mech., EAACE, EACE, and PLC)
POSTAL ADDRESS: MECHANICAL ENGINEERING DEPARTMENT
FACULTY OF ENGINEERING
KYAMBOGO UNIVERSITY
P O BOX 7181
KAMPALA
UGANDA
E-Mail Address: [email protected]
Tel: Mob. O752651993, O785610681
Home, 0414690729
ABSTRACT
The drilling machine is a machine tool (a machine that is used for making machines). The end user of this machine is always the operator, who must be trained along a line which is convenient, easy to remember, and yet cover all aspects involved from start to a finished product. This article presents the GENERAL FEATURES of the drilling machine, the MOTIONS available on it, the WORK HOLDING methods used, the TOOL HOLDING methods used and the OPERATIONS, i.e. surfaces that are produced on the drilling machine. This order of introducing the material to the operator is easy to remember, convenient and interesting. Aspects of machining principles and tool geometry are also covered, giving the operator knowledge on everything involved, which are, the machine with its motions, work piece which is properly held and tool that is properly ground and held on the machine. The general features, motions, tool holding, work holding and operations present clear drawings made in Solid Environment of Solid Edge Program, giving pictorial views that are easy to understand. This article is therefore suitable for instructors of first learners of the drilling machine and users of the machine out there in the field.
INTRODUCTION
The study of the drilling machine requires a special approach that is easily followed and clearly understandable.
Information on the use of the drilling machine is scattered and usually require some prior knowledge before it can be fully understood.
In this article all the necessary information are collected and put together in an orderly manner, making it a one stop centre that is very convenient for the instructor and quick reference for the drilling machine user. Once this approach is understood on one machine tool, (the drilling machine), it becomes very easy to learn about the other machine tools by seeing the same applied to the rest of the other machine tools.
GENERAL OBJECTIVES.
To produce a format of learning about the drilling machine that is easy and clearly understandable.
SPECIFIC OBJECTIVES.
To demystify machining principles.
To demystify the tool and its angles.
To show methods of dimension control.
To show general features of the drilling machine.
To show the motions on the drilling machine.
To show the methods of work holding on the drilling machine.
To show the methods of tool holding on the drilling machine.
To show operations that can be done on this machine.
PROBLEM STATEMENT
Accessible as it is, the drilling machine is dangerous, especially in developing countries, which need it most and are struggling to catch up with industrialization and therefore in need of an approach that demystifies all aspects of this machine tool instantly.
METHODOLOGY
This is a product of long years of unrecorded observations combined with long experience in the teaching profession and service in the industry. The literatures I accessed and used clearly revealed the problem and this pushed me through long and stressful experience of acquiring knowledge of Solid Edge as a communication drawing tool to present the findings. There are therefore no data to analyze and discuss for results. Everything presented here is original, based on knowledge acquired professionally through contacts while studying as a student, and all forms of literature while executing my duties, both at station and in industry.
THE DRILLING MACHINE
(Definition of machine tool should come out clearly, together with the explanations as to why they became a requirement).
Traditionally, any machine we see is produced with the he help of another machine. These machines which are used to produce other machines are called MACHINE TOOLS and the drilling machine is just one of them.
The very first machines however were manually made by highly skilled men who could work within the required accuracy.
With time however, higher and consistent degree of accuracy came into demand, together with greater forces required, and with increased rate of production due to demand, machines became a requirement in the production process.
INTRODUCTION TO DIMENSION CONTROL AND INSPECTION
(Explain the two types of fit that obtain between any two parts when assembled and how they are achieved using the three methods below).
Any complete machine is composed of numerous parts, which are produced separately and then assembled. The processes of producing each of those parts involve careful dimension control to suit the required type of fit. When assembled, the two parts are fitted while bearing either of the following two points in mind:-
A fit that allows relative movement between the two ( clearance fit)
A fit that does not allow relative movement between the two (interference fit)
There are three ways of achieving this.
Using individual assembly method,
Using selective assembly method,
Using Systems of Limits and Fits.
INDIVIDUAL ASSEMBLY
In this approach, one of the two parts to be assembled is first machined as close as possible to the required dimension in the working drawing. The second part is then machined while testing using the first piece until when the required fit is attained (clearance or interference).
The disadvantage of this method is that it is slow due to the numerous stoppages required for the frequent checks. It also needs highly skilled personnel for operating the machine. The parts are made for each other and may not fit properly with any other part made for the same purpose. All the above reasons make this method very costly.
SELECTIVE ASSEMBLY
This approach takes into account the fact that it is impossible to produce a particular size on many components and be consistently exact, yet the small variations do not necessarily render the work piece useless. All parts with sizes that fall within acceptable range (tolerance) must therefore be used by selecting the pairs, which fit with each other for the required fit (clearance or interference).
For this reason, all parts produced are carefully measured to find out the range of sizes in which they fall. It therefore becomes possible to sort them according to sizes that fall within the same range and therefore be able to determine which ones do produce the right fit when assembled.
Hole Shaft
For clearance fit For interference fit
B fits with a (Red) A fits with b (Yellow)
C fits with b (Black) B fits with c (Green)
D fits with c (Blue) C fits with d (Grey)Holes and shafts of particular ranges of sizes are separated in groups, which are marked, tagged or color-coded to make them readily identifiable. Groups of shafts and holes, which give the right fit when assembled, bear the same mark, tug or color code.
Much as this method may not require very high skill from a machine operator, making it slightly faster, it demands very high skill at the sorting stage, with measuring instruments of higher degree of accuracy. These instruments are also expensive.
Because parts are selected according to groups during assembly, for machines produced using
this method, replacement of broken parts during repair are done by replacing the part with a whole assembly, which includes the broken part. If for example, the hole is worn out and the shaft is still in good condition, even the shaft is replaced.
SYSTEMS OF LIMITS AND FITS
In this method, sizes of all components are determined by the designer at the designed stage and given limits within which a particular size on a component must fall.
.
All these take place in the mind of the designer only. It becomes known to any other person only after the designer has put it down in drawing. This however can be transformed into components only if the designer produces a working drawing with the right limits determined by him.
What are limits?
(Explain the concept of tolerance and make sure that they understand that it is impossible to produce the same size on different components again and again).
Because of machine error that depends on the machine condition and human error that depends on several factors, it is impossible to do machining and produce a size and say with certainty that the size obtained is the actual size, because even if the size has actually been got, there is human error in taking the measurement from the workpiece onto the measuring instrument and another in reading correctly to get the size indicated on it. On top of that is the error of the instrument, which depends on its accuracy.
The problem is even compounded when dealing with hard materials like metals, since small size variations in the order of thousands of a millimeter do matter a lot at assembly stage, and obtaining the right fit may not be possible.
This is why setting limits is very important. It is only the designer who knows what limits to set for a particular size in order to obtain a fit, which works best on the machine when properly assembled.
HOLE SHAFT
Dimension control during material removal is directly related to the amount (volume or weight) of material that remains on the final product (the component). Therefore, by setting limits, the designer sets the maximum and minimum size (and therefore weight or volume) of a component. This makes it possible to produce from one working drawing any number of that component, and all of them will be acceptable to the designer as long as their sizes fall within the limits specified in the working drawing.
The implication is that the component has conditions of maximum amount of material acceptable (maximum metal condition), and minimum amount of material acceptable (minimum metal condition).
It is then up to the machine operator to use the working drawing and produce components with sizes that fall within these limits for them (the components) to be acceptable.
There are three ways of controlling the sizes:-
Direct measurements using measuring instruments of the right accuracy.
Gauging using limit gauges.
Comparing using comparators.
DIRECT MEASUREMENTS
(Note the procedure in this approach and point out the fact that this is possible only with a skilled operator).
In order to produce components whose sizes lie within the specified limits, the machine operator must not only know how to operate the machine for metal removal purposes, but also know how to take measurements properly using the instrument, and read the instrument down to the required accuracy. In this process, the operator stops the machine after passes of metal removal and takes the size of the remaining material (shaft or hole). The main aim is to see if the size
falls within the one specified in the drawing. However with each pass of metal removal one of the following three situations is likely to result in both shaft and hole cases:-
For shafts, 1) The size is above the upper limit, meaning that the component is not yet acceptable because the weight or volume is still more than the one specified and the metal removed is insufficient. The next action from the operator is to remove more material.
2) The size is within the limits, meaning that sufficient metal has been removed and the component is acceptable. The next action is to remove it from the machine and it is ready for use or storage.
3) The size is below the lower limit, meaning that the metal removed is in excess and the component has less weight or volume than the one specified. The next action is to remove the component from the machine and discard it off, it is scrap.
For holes,
1) The size is above the upper limit, meaning that the material removed is in excess and the component has less weight or volume than the one specified. The next action is to remove the component from the machine and discard it off, it is scrap.
2) The size is within limits, meaning that sufficient metal has been removed and the component is acceptable. The component is removed from the machine and it is ready for use or storage.3) The size is below the lower limit, meaning that the component is not yet acceptable because the weight or volume is still more than the one specified and the metal removed is insufficient. The next action from the operator is to remove more material.
The main thing to note about direct measurement is that the actual size of the component is known because the operator reads it on the instrument to make sure that it falls within the required limit before accepting it. The operator must therefore be highly skilled.
The next two methods however only check whether or not the size falls within the specified limit. The operator does not know the real size.
GAUGING
(Explain the procedure and state clearly that this approach is fast easy but expensive and recommended only for mass production).
This is done using a special instrument called gauge, which has two sizes available on it. One size is corresponding to the upper limit and the other one is corresponding to lower limit. It is therefore possible to gauge using this instrument to see if the size produced on the component falls within the specified limit before accepting it.
Using this method requires many gauges since every size must have its own gauge with the right limits.
Gap gaugePlug gauge
Ring gaugeThe gauge is put in use during the metal removal process at the machining stage by the operator.
After some metal removal passes, the operator offers the GO side the gauge to the size being machined on the component. In so doing, the operator is expecting this side of the gauge to be