DEMONSTRATION.

. 1 Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 2
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.
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
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:-
1) A fit that allows relative movement between the two ( clearance fit)
2) A fit that does not allow relative movement between the two (interference fit)
There are three ways of achieving this.
1) Using individual assembly method,
2) Using selective assembly method,
3) 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). Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 3
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. Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 4
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?
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.
Hole tolerance
Nominal
hole size
Maximum
hole size
Minimum
hole size
Nominal
Shaft size
Minimum
shaft size
Maximum
shaft size
Shaft
tolerance Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 5
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:-
1) Direct measurements using measuring instruments of
the right accuracy.
2) Gauging using limit gauges.
3) Comparing using comparators.
DIRECT MEASUREMENTS
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. Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 6
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
This is done using a special instrument called gauge, which has two sizes available on it. One size
corresponding to the upper limit and the other one 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. Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 7
Gap gauge
Gap
Gap
Gauge
Workpiece
(shaft) Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 8
Plug gauge
Ring gauge
The 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 accepted at the machined
dimension. The process goes on in conjunction with metal removal until this side actually goes. This then
marks the end of metal removal process for this dimension.
The big question is whether or not the size obtained falls within the limits specified by the designer. The
answer to this question depends on what happens when the NOT-GO side of the gauge is offered to the
same size on this work piece being machined and the work piece is still on the machine. This is what the
operator wants to find out immediately, so he offers the NOT-GO side of the gauge to the dimension
expecting it to either GO or NOT-GO depending on how much material he took care to remove in the last
metal removal pass during the time he was checking the size using the GO side of the gauge. This is a
crucial decision making moment and is done only by the machine operator who must interpret correctly the
status of the work piece when the NOT-GO side of the gauge is offered to this machined size, he must also
Workpiece
(hole)
Gauge
Workpiece
Gauge Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 9
be sincere because any bad component taken as acceptable at this stage will be very difficult to detect with
the naked eye. The effect can only be felt when it is put to use.
The act of checking with the NOT-GO side of the gauge is to make sure that this side of the gauge actually
does not go, for the component to be acceptable because it will mean that the size produced as a result of
metal removal in the last pass falls within the required limits.
If it happens so (does not go), the component is removed from the machine as a finished product, which is
ready for use or storage.
The other observation expected by the operator when checking with the NOT-GO side of the gauge is for
this side to also go the way the GO side did go. This would mean that the amount of metal removed in the
last metal removal pass was in excess of what he should have, and therefore the size produce as a result
falls outside the required limits. The component is a reject (SCRAP).
Since all components are made from some material whose original weight or volume is either equal or
more than that of the component, it is not difficult to see that the condition in which the original material,
the work piece, is left in is either the same or less in weight or volume. Where metal removal is not
involved only the shape or the original material changes whereas both weight and volume remain the
same. This means that the condition of the original material has not changed in terms of weight and
volume. However where metal removal is involved, both weight and volume must reduce. Sizes therefore
play a big role in determining metal condition of the finished component in terms of weight and volume.
The limits set by the designer, in fact, set the maximum and minimum metal condition of the component.
These two conditions are therefore very easily checked using the gauge since the GO gauge checks the
maximum metal condition acceptable by the designer and the NOT-GO gauge checks the minimum metal
condition allowed. This is true for ALL gauges be it for shafts or for holes. Dimension control using
gauges does not require high skill and it is fast and easy. However, the initial cost or capital input is
enormous due to the total cost of gauges required since each size requires a separate gauge and gauges are
very expensive. This method of dimension control is recommended only for mass production.
COMPARATORS
Comparators are more advanced measuring instruments, which are used, for either inspection in mass
production of components produced using universal machine tools, or continuous dimension control in
automatic machines tools or machining centers.
Their working principle is basically comparison. For a given dimension, the instrument is set using two
sample pieces. One sample piece has the actual size equal to the upper limit size of the component and
another sample with the actual size equal to the lower limit size of the component. Since the two sizes are
different, the indicator on the instrument will assume one position when the sample with lower limit size is Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 10
used and another position when the sample with the upper limit size is used. The signal from the sample is
magnified, making it possible to see with the naked eye the difference between the sizes of the two sample
pieces. This becomes a zone that represents the limits set by the designer on the working drawing. It
therefore becomes very easy to compare the size of a component with the ones used for setting the two
limits. Any size, which falls within the zone, is acceptable. Those that fall outside the zone are either
corrected or scrapped.
In existence are mechanical, electrical, pneumatic and hydraulic comparators. Attempts are made to make
the zone clearly visible using color zone or color liquid.
It is obvious, the fact that these instruments are very expensive although very easy to use and are very
accurate. Just like in the case of using gauges, comparators are used only for quality control and mass
production.
What are fits?
Parts are made to work together after assembling a complete machine. During assembly, the worker must
pay attention to the fact that some parts are assembled to allow relative movement between each other and
others do not allow relative movement.
In individual assembly, this is taken care of by the machine operator who is himself skilled.
In selective assembly, this is done at the sorting stage where parts are matched or selected and color-coded
for storage. It is important to note that there are no rejects here since all parts are matched according to
how they fit best.
In the system of limits and fits however, this is taken care of at the design stage by the designer who sets
limits for every size. Therefore, ALL parts produced within their limits are interchangeable, and will fit
perfectly during assembly and fully serve the purpose for which the machine was designed. This is because
only parts whose sizes fall within the limits set by the designer are cleared as good by the machine operator.
There are three types of fits technically known as CLEARENCE FIT, INTERFERENCE FIT and
TRANSITION FIT.
The term FIT refers to shaft assembled with hole to produce either relative movement between each other
or no relative movement at all between each other. The designer knows where relative motion is required
and where it is not required. He therefore sets limits, which guarantees either free movement or no
movement in the right places. It is therefore logical to try to see what goes on inside the designer’s mind at
this stage by studying the types of fit in detail. Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 11
CLEARENCE FIT
HOLE SHAFT
UHL= Upper hole limit NS= Nominal size USL= Upper shaft limit
LHL= Lower hole limit LSL= Lower shaft limit
The tolerance zone of the hole is above that of the shaft and between them is a gap, which is a minimum
allowance chosen by the designer to guarantee clearance fit between the two during assembly. Clearance
fit is therefore an imaginary arrangement of shaft and hole working drawings brought together and
assembled to show that the largest acceptable shaft is still smaller than the smallest acceptable hole or the
smallest acceptable hole is still larger than the largest acceptable shaft. Designers know that this fit allows
relative movement between the two parts.
Since any shaft or hole, whose size falls within the limits is acceptable it can easily be seen that the
minimum clearance allowance possible for this fit is the difference between the smallest hole and the
biggest shaft, and the maximum clearance allowance is the difference between the biggest hole and the
smallest shaft. The magnitude of the allowance is very important and the designer takes care to make sure
that the minimum allowance is there but as small as possible and the maximum allowance is big enough
but does not affect the performance of the assembly. When clearance allowance is too big, some parts
acceptable as good do assemble with too much ease to make very loose joints with short life span and very
noisy when put to use.
Hole tolerance
Gap
UHL LHL
NS NS LSL USL Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 12
INTERFERENCE FIT
HOLE SHAFT
UHL= Upper hole limit NS= Nominal size USL= Upper shaft limit
LHL= Lower hole limit LSL= Lower shaft limit
The tolerance zone of the hole is below that of the shaft and between them is a gap, which is a minimum
allowance chosen by the designer to guarantee interference fit between the two during assembly.
Interference fit is therefore an imaginary arrangement of shaft and hole working drawings brought together
and assembled to show that the smallest acceptable shaft is still larger than the largest acceptable hole or
the largest acceptable hole is still smaller than the smallest acceptable shaft. Designers know that this fit
does not allow relative movement between the two parts.
Since any shaft or hole whose size falls within the limits is acceptable, it can easily be seen that the
minimum interference allowance possible for this fit is the difference between the biggest hole and the
smallest shaft, and the maximum interference allowance is the difference between the smallest hole and the
biggest shaft. The magnitude of the allowance is very important and the designer takes care to make sure
that the minimum allowance is there but as small as possible and the maximum allowance is just enough
and does not affect the assembly process or the performance of the assembly. When interference allowance
Hole tolerance
Shaft tolerance
Gap
UHL LHL
NS NS LSL USL Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 13
is too big, some parts acceptable as good are impossible to assemble and if they do, the component with
the hole is overstressed leading to either its cracking or excess strain to adjacent moving parts like balls or
rollers of bearings. This can affect the performance of the assembly in many ways. Usually the efficiency
is reduced and there is overheating which can drastically reduce the life of the machine. It also overloads
the prime mover.
TRANSITION FIT
HOLE SHAFT
UHL= Upper hole limit NS= Nominal size USL= Upper shaft limit
LHL= Lower hole limit LSL= Lower shaft limit
The tolerance zones of hole and shaft overlap. Transition fit is therefore an imaginary arrangement of shaft
and hole working drawings brought together and assembled to show that the biggest hole is bigger than the
smallest shaft and the smallest hole is smaller than the biggest shaft.
Designers know that this fit exists only on the working drawing because in reality during assembly only
clearance and interference fits are obtained with no effect at all on the performance of the machine.
Since any shaft or hole whose size falls within the limits is acceptable, it can easily be seen that the
maximum clearance allowance possible for this fit is the difference between the biggest hole and the
smallest shaft, and the maximum interference allowance is the difference between the smallest hole and the
biggest shaft.
Because of the overlap between the hole and shaft tolerance zones, there is no minimum clearance or
minimum interference. Theoretically, however there is a possibility of obtaining zero clearance or
Hole tolerance
Overlap Shaft tolerance
UHL LHL
NS NS LSL USL Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 14
interference. This happens only if the shaft and hole are of the same size, and is possible only within the
area of tolerance zone overlap.
SYSTEMS OF FIT
When shafts and holes are produced on machine tools available to the designer, tolerance limits can easily
be controlled to produce components with the sizes required for the right fit. Machine building however
involves the use of ready-made components like bearings and plain shafts. The designer then finds himself
in a situation where he can control the limits of only one of the two parts involved in the fit. Holes are also
produced easily and more accurately using standard size tools like reamers. Systems therefore refer to the
methods used to obtain the required fit, either clearance or interference, when one size is already available
and on machining operation is required, or when one size is produced using a standard size tool.
There are two systems for obtaining fits and they are based on either the hole or the shaft depending on
which one is already available with its fixed size.
Hole basis system
Between ball bearings and shaft is interference fit.
Between gear and shaft is transition fit (either clearance fit or interference fit).
Between shaft and pulley is clearance fit.
Sizes of the holes already exist:-
Ball bearings are ready made.
The hole in the gear is reamed using standard size reamer.
The hole in the pulley is reamed using standard size reamer.
The right fit is obtained by machining the shaft to the right size.
Gear
Ball bearing
Shaft
Housing
Pulley
Ball bearing Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 15
Shaft basis system
Between bush bearing and shaft is clearance fit.
Between gear and shaft is transition fit.
Between pulley and shaft is clearance fit.
The shaft is a plain one of standard size.
The required size is obtained by machining:-
The bush bearing for clearance fit
The gear for interference fit.
The pulley for clearance fit.
INSPECTION
In this section, inspection will refer to dimensions only. The methods used to inspect the sizes depend on
the type of dimension control used in the production process.
Individual assembly method does not require any inspection since the operator does the right thing either
independently or under supervision. Nothing is produced for storage, so there are no parts lying around for
inspection. Vital components are stored in an assembled form.
Selective assembly method does require minimum inspection. This is because during the sorting process
there are skilled personnel using more accurate measuring instruments. It is an extension of dimension
control that ended during the machining stage since each and every component is again measured.
Catastrophic errors however do happen, either by reading the measuring instrument wrongly or marking a
component with wrong color code and therefore putting it in a different size group.
Bush bearing
Shaft
Gear
Bush bearing
Pulley
Housing Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 16
The use of limits and fits system however require strict inspection since the parts made within limit are
assumed to work interchangeably with any other part made within limits for it. Because of this
interchangeability concept, parts that are passed as good by the worker are taken straight for use or storage
for sale.
Bearing in mind the fact that the workers are semi skilled, inspection methods used should minimize or
bring to zero the number of bad components accepted as good and therefore put to use, sold or stored.
Here the most common approach is the use of gauges. The inspection gauges are more accurate than the
ones used during production. Since gauges are also manufactured, they are also given tolerances, but the
tolerance zones of inspection gauges are smaller and fall within the tolerance zones of the size being
checked.
The GO side of the gauge always wears with time and begins accepting holes of smaller
sizes and shafts of bigger sizes.
This can be minimized or brought down to zero using different methods, depending on the volume and
method of production. In general, active GO gauges should never be allowed to wear up to the maximum
tolerance size limits of shafts, and minimum tolerance size limits of holes. Gauges must therefore be
checked frequently using very accurate measuring instruments and replaced before they begin to accept
sizes which are outside the tolerance limits.
The other approach is random sampling of finished components and replacing the measuring gauge if a
size is found to fall close to the extreme limits of the sizes.
In this case, there is a possibility of a wrong size slipping through to assembly line, or even Sales
Department.
In the assembly line, these cases are spotted out and handled either individually or selectively. However in
the Sales Department, this is a source of bad reputation, which must be avoided at all costs.
Modern approach in production has introduced methods which require constant monitoring of sizes as they
are being produced, and the measuring instruments best suited for this are comparators. They are fitted
directly on the machine, making the constant size monitoring process possible.
Once the machine is set for a particular size, only tool wear remains basically the only factor in the size
variations. As shafts become bigger and holes become smaller, a signal that switches off the machine is
sent from a command within the machine before sizes that fall outside tolerance limit zone are produced
and the tool is replaced.
Elements of inspection here are therefore the settings on the machine and the settings on the tool, and all
parts produced are absolutely interchangeable and can be used, stored or soled without any worry. Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 17
MACHINING PRINCIPLES AND METAL CUTTING TOOLS
The following are daily life principles that equally do apply to machining of metals and cutting tools:-
1) For any tool to be able to cut another material, the tool must be harder than that material,
just like knife cuts bread because it is harder than bread.
2) Two materials or objects will never occupy the same space at any one given time. If an
attempt is made to force them into that one space, there must be collision or accident and
the stronger material displaces the weaker one and occupies the space.
3) The tool must have angles around the cutting edge to make the cutting edge stand alone in
space so that it touches the material at the cutting edge only for maximum cutting or tearing
effect.
4) There must be an effective work holding provision, a device that leaves the work firm and
rigid on the machine.
5) There must be an effective tool holding provision, a device that leaves the tool firm and
rigid on the machine.
6) There must be controlled motions on the machine, to force work and tool into each other,
with contact between work piece and tool at cutting edge only.
TOOL ANGLES
All attempts must be made to understand the position or location of the following angles in relation to the
cutting edge of the tool and some particular motions on the machine. The angles are PLAN APPROACH
angle, PLAN RELIEF (or TRAIL) angle, FRONT CLEARANCE angle, SIDE CLEARANCE angle,
FRONT RAKE, and TRUE RAKE angles. These angles are shone on the turning tool below, but they can
be identified on any other metal cutting tool.
New tool without cutting edge
Cutting Edge
Plan approach Angle
(seen from above)
Imaginary line parallel to cutting
feed motion.
Direction of
Cutting feed Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 18
Positive front rake
Imaginary line parallel to
cutting feed motion.
Plan relief (Trail) angle
(seen from above)
Side clearance angle (seen in
direction parallel to cutting edge)
Cutting edge
Direction of
Cutting feed
Front rake angle
(seen in the direction
parallel to cutting
feed)
Cutting
feed
Lathe spindle
axis
Direction of
Cutting feed Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 19
Negative front rake
Positive side rake
Negative side rake
Front rake angle
(seen in the
direction parallel to
cutting feed)
Cutting
feed
Lathe spindle
axis
Lathe spindle
axis
Cutting
feed
Side rake angle
(seen in the
direction
perpendicular to
cutting feed)
Cutting feed Lathe spindle
axis
Side rake angle
(seen in the
direction
perpendicular to
cutting feed)
Front clearance angle
(seen in the direction
parallel to spindle axis)
Lathe spindle
axis
Cutting feed Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 20
Finished tool
True rake angle
(positive) seen in
direction parallel to
cutting edge
Cutting feed
Cutting edge
Lathe spindle axis
True rake angle
(negative) seen in
direction parallel to
cutting edge
Lathe spindle axis
Cutting feed
Cutting edge
Cutting feed
Cutting edge Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 21
THE DRILLING MACHINE
There are four types of drilling machines in common use:-
1) The Sensitive Drilling Machine
Genera Features
This machine is small in size and power. It is either floor mounted or pedestal, (mounted on a raised
surface or table).
Motor shaft
Pulley shaft
Stepped pulley
Sleeve
Spindle
Chuck
Tool
Table
Pillar
Base
1
2
3
4
Stepped pulleys and motor
inside Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 22
The spindle is powered from a small motor through a stepped pulley to provide four or more different
speeds. Power is available only to the spindle rotation. All other motions are manual.
Motions
Motion 1- Rotary motion of the spindle. This is the main motion.
Motion 2- Linear motion of sleeve parallel to spindle axis and perpendicular to table surface. This is the
only feed motion available on this machine.
Motion 3- Linear motion of table of table perpendicular to its own surface and parallel to motion 2 and
spindle axis. This motion is only for setting the position of the table depending on the height of the work
piece, tool length and stroke of motion 2.
Motion 4- Angular motion of table about pillar axis parallel to its own surface. this motion is for setting
hole position directly below tool axis.
Work holding
Handholding
This is recommended for either small drills or heavy work pieces whose weights can stand against the
power of the spindle drive. Thin sheets should never be hand held since it can easily be ‘picked’ by the
tool and have it rotating with it, endangering the operator’s hand.
Hand clamp
This is for tiny pieces or thin plates where hand grip provides insufficient power to counter that of the
spindle power.
Tool
Machine table
Workpiece held
by hand Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 23
Hand-held drill vice
Most work can be conveniently clamped in the vice. The vice itself is then hand-held provided the drill is
not too big. Deep holes are produced more accurately since the vice aligns the work piece automatically
with the spindle axis and table surface.
Clamping directly on the table
When drilling big holes, the holding power required is big. If the work piece is of awkward shape it is
recommended to clamp directly on the table. This is done using tee-bolts in the tee-slots provided on the
table, or using G-clamp.
Tool
Workpiece in a clamp
held by hand
Machine table
Wing nut
Bolt
Hand
Clamp
Tool
Vice
Workpiece in a vice
held by hand
Machine Table Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 24
On a vice clamped on the table
Work piece that can be accommodated in a vice must be held in a vice, and if the cutting power is big the
vice should be clamped onto the table using tee-bolts in the tee-slots provided on the table.
Tool
Workpiece
Table
Tee-bolt
Clamp
Packing
Tool
G-Clamp
Workpiece
Table Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 25
Tool holding
The only tool holding position is the spindle. It is done in much the same way as on the lathe tailstock. The
tool however must have the same taper size as that on the spindle. If the spindle taper is big then a sleeve
is used to fit in between the spindle and the tool.
Tool
Vice
Workpiece
Tee-slot
Tee-bolt
Table Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 26
Spindle Drift slot
Tool tongue
Tool taper
Spindle
Tool
Sleeve taper
Sleeve tongue
Sleeve drift slot
Tongue
Taper
Chuck
Tool Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 27
Operations
The result of all operations is always a surface of some form produced. This comes about as a generated
surface using single point tool or copying the form from the tool onto the work piece.
In both cases it is possible to produce a surface only if at least two motions of the machine are present at
the same time. These are active motions, one of which must be spindle rotation, which is the main motion.
Another motion, which is very important but does not exist during actual cutting process is the one used to
set the cutting depth. This is passive motion. It is the motion used to give the work piece its size.
Drilling.
This operation produces a hole where there is none.
-Motion 1- Active spindle rotary motion (main motion)
-Motion 2- Active cutting feed motion.
The length or depth of hole depends on sleeve stroke and the position of the table on the pillar and above
all tool length.
All small drills are held in the chuck which fits in the spindle taper.
It is however important to note that small drills are likely to break when exposed to forces bigger than the
ones they can handle. This condition is unavoidable when drilling through holes because when the drill is
breaking through the other side as it penetrates the work piece, the cut surface area keeps reducing and if
the feeding force does not reduce, then the tool begin to take thicker and thicker cuts, known as ‘bite’,
which increases load on the tool and may prove too big if not reduced. Since this machine is not fitted with
automatic feed, the operator feels (senses) the drill breaking through the work piece because the feeding
force reduces. The operator then reduces the feeding rate and therefore avoids excess force on the tool.
This is why it is called ‘sensitive drilling machine’.
1
2
Tool (drill)
Workpiece Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 28
All the following operations are carried out in the same way as drilling, with the only difference being the
tool.
Counter drilling.
This operation enlarges an existing hole.
-Motion 1- Active spindle rotary motion (main motion)
-Motion 2- Active cutting feed motion.
Reaming.
This operation improves the surface finish and size of an existing hole.
-Motion 1- Active spindle rotary motion (main motion)
-Motion 2- Active cutting feed motion.
Tool (bigger drill)
1
2
Bigger hole
Workpiece
Smaller hole
1
2
Tool (reamer)
Reamed hole
Smaller drilled hole
Workpiece Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 29
Counter boring.
This operation produces hole with a flat bottom on top of a smaller one. This
becomes a recess for hiding the head of a bolt or screw below a surface.
-Motion 1- Active spindle rotary motion (main motion)
-Motion 2- Active cutting feed motion.
Counter sinking.
This operation produces a counter sink hole on top of a smaller one. This becomes a recess for hiding the
head of a counter sink bolt or screw below a surface.
-Motion 1- Active spindle rotary motion (main motion)
1
2
Counterbore hole
Tool (counterbore)
Workpiece
Bolt/screw hole
1
2
Tool (countersink)
Countersink Hole
Screw hole
Workpiece Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 30
-Motion 2- Active cutting feed motion.
Spot facing.
This operation is for cleaning the top of a hole in a casting. Castings usually have poor surface finish and
geometry; therefore, the surface must be cleaned if the bolt head, nut or washer is to sit properly on top of
the hole.
-Motion 1- Active spindle rotary motion (main motion)
-Motion 2- Active cutting feed motion.
2) The Pillar Drilling Machine
This is a bigger version of the sensitive drilling machine provided with spindle power through gear box
unlike belt driven in the sensitive drilling machine. This is what provides the spindle with the different
ranges of speeds. The table is round and has an additional angular setting motion. Feed motion is also
provided with power.
General Features.
1
2
Bolt head seat
Tool (spot facer)
Casting
Screw hole Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 31
Motions.
Motion 1- Rotary motion of spindle. This is the main motion.
Motion 2- Linear motion of sleeve, parallel to spindle axis and perpendicular to table
surface.
Motion 3- Linear motion of the table up and down the pillar, parallel to spindle axis and
perpendicular to the table surface. This motion is only for setting the position of the table
depending on the height of the work piece, tool length and stroke of motion 2.
Motion 4- Angular motion of table about pillar axis parallel to its own surface. This motion
is for setting hole position directly below tool axis.
Motion 5- Angular motion of table about its axis, for setting hole position directly below
spindle axis.
Work holding.
All the methods used on the sensitive drilling machine are used here sensibly since the spindle taper is
bigger, accepting bigger tools and much bigger vices can be used on this machine.
This machine is powerful, with provision to use tools for heavy material removal. Since most of the work
done here require huge forces, work holding must be completely restrictive. Tee-slots are provided on the
1
2
Sleeve
Spindle
3
4
5
Table
Table arm
Pillar
Gearbox
Head
Base
Tool Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 32
table for this purpose. With the work piece restricted onto the table, putting the hole position below the
tool axis is done as follows:-
1) The table arm is released from the pillar lock.
2) The table is released to be free to rotate about its own axis.
With the two motions freed, the hole position can be brought below tool axis as shown in the diagram
below.
In practice, the two motions are steered simultaneously while checking the position with the tool.
Tool holding and operations are the same as on the sensitive type, however the spindle taper hole is bigger.
3) Box Column Drilling Machine
Unlike the pillar type, which stands on a pillar, this machine is supported on a box column for better
rigidity. The table is also supported on a height adjustment screw, making the table very rigid, unlike that
of the pillar type, which simply hangs on the pillar.
The table is also provided with tee-slots for clamping purposes as on other drilling machines. This
machine is however supplied with a compound table, which has two mutually perpendicular motions for
very accurate setting of the work directly below the tool. Once the compound table is bolted on the
machine table and the work piece bolted onto the compound table, any position of the work piece can be
brought under the tool using the two motions of the compound table.
4
5
Table arm
Tool axis
Hole position
Table
Workpiece (clamped)
Pillar Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 33
General Features.
Motion 1- Rotary motion of the spindle. This is the main motion.
Motion 2- Linear vertical motion of sleeve parallel to spindle axis and perpendicular to table surface.
Motion 3- Linear vertical motion of table parallel to spindle axis and perpendicular to its own surface.
1
Spindle 2 Sleeve
Tool
Table
Tee-slot
3
Support screw
Base
Box column
Gearbox
Head Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 34
Work Holding On Compound Table.
4) Radial Drilling Machine.
This machine is made of different sizes and power. On this machine, it is the tool which is brought directly
above the hole position. Since the work piece is fixed, heavy components can be easily drilled right from
the floor without any clamping. It is however supplied with two auxiliary tables and therefore making it
possible to preset the work on one table while drilling is going on using the other table, thus increasing the
speed of production.
General features.
Motions.
Motion 1- Rotary motion of the spindle. This is the main motion.
Longitudinal motion
Transverse motion
Bolthole
Tee-slots
2
1
4 3
5
Drilling head
Radial arm
Sleeve
Spindle
Tool
Base/Table
Pillar Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. 35
Motion 2- Linear motion sleeve parallel to spindle and
perpendicular to table surface.
Motion 3- Linear motion drilling head along the radial arm, horizontal and parallel to table
surface.
Motion 4- Angular motion of radial arm about the pillar, parallel
to table surface.
Motion 5- Linear vertical motion of arm along the pillar, parallel
to spindle axis and perpendicular to table surface.
Using motions 3 and 4 the tool can be brought directly above the hole position by following any path.
Pillar
4
3
Drilling head
Radial arm
Tool axis
Hole position
Workpiece
1st
2nd
Radial line Prepared by Okwany Amos. NOT FOR SALE. © Kyambogo University. Tool Guidance riefly and concisely explain what you do for your audience.

Use this paragraph section to get your website visitors to know you. Write about you or your organization, the products or services you offer, or why you exist. Keep a consistent communication style. Consider using this if you need to provide more context on why you do what you do. Be engaging. Focus on delivering value to your visitors.