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PARUL PLOYTECHNIC INSTITUTE (LIMDA)
MECHANICAL DEPARTMENT (5TH SEM)
MACHINE TOOL TECHNOLOGY (351903)
LABORATORY MANUAL
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CERTIFICATE
This is to certify that Shri / Kum. _____________________________________________________________Registration number ___________________________________Of Programme Diploma in _____________________________________ has satisfactorily completed the term work in course code (351902) Course MACHINE TOOL TECHNOLOGY within four walls of this Institute.
Date of Submission:
Staff in charge
Head of Department
Name of Institute: ________________________________________________________
Name of the Student:-_________________________________________________________
| | | | | | |
|1 |PREPARATORY ACTIVITY. | | | | |
|2 |MINI PROJECT. | | | | |
|3 |KINEMATICS AND MOTION TRANSMISSION SYSYTEM. (GRINDING MACHINE &| | | | |
| |LATHE MACHINE ) | | | | |
|4& 5 |TO PRODUCE JOB ( COMPLEX JOB ) WITH VARIOUS MACHINING METHODS. | | | | |
|6 |GEAR CUTTING | | | | |
|7 |THREAD CUTTING | | | | |
|8 |PRESENTATION | | | | |
|9 |TECHNICAL VISIT | | | | |
Signature of Teacher Total Marks: .
EXPERIMENT: - 01
PREPARATORY ACTIVITY
GRINDING VARIOUS CUTTING TOOL ANGLES
AIM: - To grind single point cutting tool.
• ?>Material and Equipment
-Bench grinder one side rough grinding wheel and on other hand side polish grinding.
-M.S. square of 15x15mm ,150 mm long
-Set of angle gauge
-Grinding goggles
• Tool geometry
Tool shape
Shank: - It is the part of the solid tool which is held in tool holder, mostly of rectangular cross section.
Neck: - It is extension of the shank but reduces sectional area.
Face: - It is the top surface of the tool on which the chip flows.
Heel: - It is the end of the base immediately facing the work piece.
Base: - It is bottom of shank and bears the support taking tangential pressure of the cut.
• Tool signature
The earlier system of giving angles to the tools was purely based on experience. This system was all right when the production rate was not high. With the advent of mass production techniques and high production rate. The earlier system is not longer effective and a need was felt for standardization of cutting tool angles.
Different angles required to specify the tool geometry are always given in a particular order which is known as tool signature.
Tool signature with positive rectangle & clearance angle
8° 7° 7° 9° 6° 10° 15
Back rack angle
Side rack angle
End relief angle
Side relief angle
End cutting edge angle
Side cutting edge angle
Nose radius
Tool Angle
• Lip angle: - The angle between the face and the end of both flange of the tool is known as lip angle.
• Back rack angle: - It is the angle between the face of a tool and shank base measured in plane at right angles to the base and parallel to the central line of the nose.
• Side rack angle: - It is the angle between the face of the tool and a plane parallel to the tool base, measured in a plane at right angle to the base and the side cutting edge.
• End relief angle: - It is the angle between the plane perpendicular to the base and the end flange.
• Side relief angle: - It is the angle between the side flange of the tool and a line drawn perpendicular to the base.
Some Important Terms
• Cutting Speed: - It may be defined as the distant which tool travels along the material in one minute. Its unit is m/min.
Cutting Speed = πDN m/min
100
• Feed: - The feed may be defined as the distance through which the tool advances into the work piece during one revolution of the work piece. Its unit is mm/rev.
• Depth of cut: - It may be defined as the amount by which a tool or cutter is inserted into the work piece metal during one cut.
• Metal removal rate: - The Metal removal rate is the volume of metal removed in unit time.
EXPERIMENT: - 02
MINI PROJECT
AIM: Manufacture the assembly which is designed in design of machine element (knuckle joint or cottar joint).
Or
Prepare the power point presentation of given data.
PRACTICAL NO.:- 3
GRINDING MACHINE
AIM: - TO STUDY ABOUT GRINDING MACHINE.
INTRODUCTION CUTTING ACTION OF GRINDING WHEEL.
Grinding is the most common form of abrasive machining. It is a material cutting process which engages an abrasive tool whose cutting elements are grains of abrasive material known as grit. These grits are characterized by sharp cutting points, high hot hardness, and chemical stability and wear resistance. The grits are held together by a suitable bonding material to give shape of an abrasive tool.
[pic]
Fig. Cutting action of abrasive grains
Fig. illustrates the cutting action of abrasive grits of disc type grinding wheel similar to cutting action of teeth of the cutter in slab milling.
• Grinding wheel and work piece interaction
The bulk grinding wheel-work piece interaction as illustrated in Fig. can be divided into the following:
1. grit-work piece (forming chip)
2. chip-bond
3. chip-work piece
4. bond-work piece
Except the grit work piece interaction which is expected to produce chip, the remaining three undesirably increase the total grinding force and power requirement.
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Fig. Grinding wheel and work piece interaction
Therefore, efforts should always be made to maximize grit-work piece interaction leading to chip formation and to minimize the rest for best utilization of the available power.
• Interaction of the grit with the work piece
The importance of the grit shape can be easily realized because it determines the grit geometry e.g. rake and clearance angle as illustrated in Fig. 27.4. It appears that the grits do not have definite geometry unlike a cutting tool and the grit rake angle may vary from +450 to -600 or more.
γ (+ve) γ (-ve)
α α
Fig. Variation in rake angle with grits of different shape
Grit with favorable geometry can produce chip in shear mode. However, grits having large negative rake angle or rounded cutting edge do not form chips but may rub or make a groove by plugging leading to lateral flow of the work piece material.
• Grinding wheels
Grinding wheel consists of hard abrasive grains called grits, which perform the cutting or material removal, held in the weak bonding matrix. A grinding wheel commonly identified by the type of the abrasive material used. The conventional wheels include aluminum oxide and silicon carbide wheels while diamond and CBN (cubic boron nitride) wheels fall in the category of super abrasive wheel
Compositional specifications
Specification of a grinding wheel ordinarily means compositional specification. Conventional abrasive grinding wheels are specified encompassing the following parameters.
1) The type of grit material
2) The grit size
3) The bond strength of the wheel, commonly known as wheel hardness
4) The structure of the wheel denoting the porosity i.e. the amount of inter grit spacing
5) The type of bond material
6) Other than these parameters, the wheel manufacturer may add their own identification code prefixing or suffixing (or both) the standard code.
• Marking system for conventional grinding wheel
The standard marking system for conventional abrasive wheel can be as follows:
51 A 60 K 5 V 05, where
• The number ‘51’ is manufacturer’s identification number indicating exact kind of abrasive used.
• The letter ‘A’ denotes that the type of abrasive is aluminium oxide. In case of silicon carbide the letter ‘C’ is used.
• The number ‘60’ specifies the average grit size in inch mesh. For a very large size grit this number may be as small as 6 where as for a very fine grit the designated number may be as high as 600.
• The letter ‘K’ denotes the hardness of the wheel, which means the amount of force required to pull out a single bonded abrasive grit by bond fracture. The letter symbol can range between ‘A’ and ‘Z’, ‘A’ denoting the softest grade and
‘Z’ denoting the hardest one.
• The number ‘5’ denotes the structure or porosity of the wheel. This number can assume any value between 1 to 20, ‘1’ indicating high porosity and ‘20’ indicating low porosity.
• The letter code ‘V’ means that the bond material used is vitrified. The codes for other bond materials used in conventional abrasive wheels are B (resinoid), BF (resinoid reinforced), E(shellac), O(oxychloride), R(rubber), RF (rubber reinforced), S(silicate)
• The number ‘05’ is a wheel manufacturer’s identification.
PRACTICAL NO.:- 4&5
AIM:- TO PRODUCE JOB & (COMPLEX JOB ) WITH VARIOUS MACHINING METHOD.
AIM:- To prepare a process plan, operation sheet and a shop floor layout for a given job.
1) Size of raw material -- 100 * 30 mm
2) Size of finished job -- 95 * 28 mm
3) Instruments & M/C – Lathe, Drilling, Shaper, Venire caliper, Scale,. etc.
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2.1- PROCESS PLAN: --
| OPERATION |TOOLS |
|FACING |FACING TOOL |
|ROUGHING |ROUGHING TOOL |
|TURNING |SINGLE POINT CUTTING TOOL |
|STEP TURNING |SINGLE POINT CUTTING TOOL |
|TAPER TURNING |SINGLE POINT CUTTING TOOL |
|GROOVING |PARTING OFF TOOL |
|KNURLING |STRAIGHT KNURLING TOOL |
|DRILLING |DRILL BIT |
|SHAPING |SHAPING TOOL |
|CHAMFERING |SINGLE POINT CUTTING TOOL |
|PROCESS FINISHING |EMERY PAPER |
2.2- STEPS :-
Take diameter 30mm* 100mm long M.S. round bar as per raw material reqd.
1. Hold the bar in the chuck.
2. Select facing tool & machining parameters for facing.
3. Carry out facing operation.
4. Remove facing tool, mount turning tool on the tool post.
5. Select machining parameters.
6. Now start turning operation roughing to produce 28mm diameter for in 95 mm length.
7. For the taper turning operation at calculation angle of swivel for compound rest by using, TANQ = (D – d)/2l.
8. After calculate angle of swivel, compound rest should be swiveled at 70 angle & set it.
9. Create taper by moving compound slide and cross slide for the depth of cut & complete the taper operation.
10. Move slide compound rest at zero degree.
11. Remove turning tool & mount grooving tool.
12. Remove the grooving tool & mount the knurling tool.
13. Perform straight knurling operation for 15mm length & diameter 28mm.
14. Mount the drilling tool on tail stock.
15. Perform drilling operation for 20mm length & diameter 10mm
16. Remove the running tool from tool post & mount the threading tool.
17. Perform threading operation for thread on 20mm length & 13 mm diameter with 1.5 mm pitch.
18. Remove the threading tool.
19. Mount the work piece & tool in shaper machine to perform shaping operation.
20. Again hold the work piece in lathe machine & mount the tool on the tool post.
21. Perform chamfering for 2 mm length at 450 angle.
22. Perform finishing operation with the help of emery paper.
2.3- OPERATION SHEET:-
|Sr.No |Description of Operation |M/c used |Depth of Cut |Name, Material & sketch of Cutting Tool |
|1 |Using raw material of 30mm diam * 100 mm length |Power Hacksaw | |Hacksaw blade |
|2 |To hold work piece in the chuck |Lathe | |Three jaw chuck |
|3 |To operate Facing operation on both side of job. |Lathe |2.5 mm |Single point cutting tool |
|4 |Perform Roughing operation to reduce diam of job. i.e. 28mm diam |Lathe |2 mm |Single point cutting tool |
|5 |Perform Step turning |Lathe |-- |Single point cutting tool |
|6 |Perform Taper turning operation |Lathe |-- |Single point cutting tool |
|7 |Grooving operation for 10mm diam in 5mm length,20mm diam in 10mm |Lathe |-- |Parting off tool |
| |length | | | |
|8 |Straight knurling operation for 28mm diam in 15mm length |Lathe |-- |Straight knurling tool |
|9 |Threading operation for 13mm diam in 20mm length |Lathe |-- |“V” tool (HSS) |
|10 |Drilling operation for 20mm length & 10mm diam. |Lathe |-- |Drill bit (HSS) |
|11 |Shaping operation |Shaper |-- |Single point cutting tool |
|12 |Perform chamfering operation for 2mm at 450 angle. |Lathe | |Single point cutting tool |
|13 |Perform finishing operation |Lathe | |Emery paper |
Table 2.1- Operation Sheet
EXERCISE
1) Explain cutting action of grinding wheel. State atleast five factors contributing to
Quality and accuracy obtainable from grinding process.
2) What do you understand by balancing of grinding wheel? How is it done?
3) Give the nomenclature of grinding wheel as per IS.
4) Write differences: 1) Dressing &Truing, 2) Honing & lapping,
3) Hard wheel & soft wheel, 4) Loading & Glazing,
PRACTICAL NO.:- 06
GEAR CUTTING
AIM:- TO STUDY ABOUT DIFFERENT METHODS OF GEAR CUTTING.
• PRINCIPLE OF GEAR CUTTING.
□ This is a speedy and accurate process of gear generation. In hobbing the cutter is called hob is like milling cutter and feed is given to it in the gear blank.
□ The hob is worm-type cutter and fluites are cut in its length which provides cutting edge.
□ The hobbing is mainly use to cut external gears.
□ Different number of spur & helical tooth can be cut on the blank using same hob of certain module
□ The worm,worm-wheel,straight and invalute splines can also be generated by this process.
➢ Gear hobbing is of three types based on
direction of feed.
1) Axial
(2)Radial
(3)Tangential as shown in fig. [pic]
• GEAR CUTTING HOB
o The construction of hob is difficult & complex in comparison to the other cutting tools.
o Involute threads are cut on the hob & cutting edge is provided in its length by cutting the flutes.
o Due to that its shape of thread obtained is like involute tooth rake having its form relieved as shown in fig.
o Hob is generally made of high speed steel& properly hardened.
[pic]
• ADVANTAGES OF GEAR HOBBING
□ (1)All most all type of gear can be cut by hobbing.
□ (2)The accuracy of gear can be maintained.
□ (3)Its rate of production is high.
□ (4)It is suitable for medium and batch production.
□ (5)The hob of single module can cut the gears having different no.of teeth having same module.
□ (6)complex indexing is not necessary in this process.
LIMITATION OF GEAR HOBBING
□ (1)Internal gears can be not be produced.
□ (2)It is difficult to cut bevel gears.
□ (3)Work piece having unequal shape and having flange & shoulder can not be considered for cutting gears on it.
□ (4)The accuracy is reduces in multistart hobbing.
4.1- GEAR TERMINOLOGY:-
Several terms commonly used in describing gears are defined as follows:--
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Figure 4.1- Gear Terminology
1) CIRCULAR PITCH: -- Length of arc of pitch circle between corresponding point inadjecent teeth.
2) ADDENDUM: -- Height of tooth space above the pitch circle.
3) DEDENDUM: -- Depth of tooth space below the pitch circle.
4) DIAMETRIC PITCH: -- Ratio of no. of teeth to no. of inches of pitch diameter.
5) PITCH CIRCLE: -- A circle of radius equal to distance from gear axis to pitch point.
6) PITCH DIAMETER: -- Diameter of pitch circle is pitch diameter.
7) PITCH POINT: -- The tangent point of pitch circles of two matting gears.
4.2- PRINCIPLE OF GENERATING AND FORMING:-
The surface reproduced by shaper or planner works on generating principle. The tool used for that in single point cutting tool. Thus the surface produced by providing definite motion to cutting edge or the cutting tool is known as generating.
The process of obtaining surface developed on the work piece made as the form tool profile is known as forming.
4.3- GEAR MILLING BY FORMING PROCESS:-
Milling machine used for manufacturing all types of gears like spur gear, helical gear, worm gear, bevel gear etc. In milling machine the cutter rotates on the spindle and work reciprocates under the cutter, once the cutter finished the tooth profile the work is indexed for next position.
There are two types of cutters used like End mill cutter & Disc cutter. End mill cutter used for big pitch of pinions & Disc cutter used for cutting big spur gear at which more material is to be removed.
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Figure 4.2- Gear Milling
4.4- MERITS OF GEAR MILLING PROCESS --
1) All types of gears like spur gear, helical gear, worm gear, bevel gear etc made.
2) It is used for rough and finishing operation both.
3) It is economical process.
4) It is used for job work.
4.5- DEMERITS OF GEAR MILLING PROCESS --
1. It is not suitable for mass production.
2. It requires more time to complete operation.
3. Precise gears cannot be produced by this method.
4.6- GEAR BROCHING PROCESS:-
Gear cutting by broaching machine is known as high production and high accuracy process. It is mainly used for manufacturing internal gears and helical gears used for high speed applications. It is also used for spur gear production.
4.7- MERITS OF GEAR BROACHING PROCESS --
1. It is convenient for internal spur gears and helical gears manufacturing.
2. It is more economical for mass production.
3. Gears with high degree of accuracy and finishing can be manufacturing.
4.8- DEMERITS OF GEAR BROACHING PROCESS --
1. It is not convenient for external gears manufacturing.
2. It is completing at very slow speed.
It is not used for bevel and worm gears manufacturing from which broach tool not passing through out.
4.9- GEAR SHAPING PROCESS:-
The cutter used in gear shaping machine is one type of gear on which cutting edge present. In this pinion or rack is used for gear cutter. This modification of the gear shaping process is defined as a process for generating gear teeth by a rotating and reciprocating pinion-shaped cutter. The cutter axis is parallel to the gear axis. The cutter rotates slowly in timed relationship with the gear blank at the same pitch-cycle velocity, with an axial primary reciprocating motion, to produce the gear teeth.
A train of gears provides the required relative motion between the cutter shaft and the gear-blank shaft. Cutting may take place either at the down stroke or upstroke of the machine. Because the clearance required for cutter travel is small, gear shaping is suitable for gears that are located close to obstructing surfaces such as flanges.
[pic]
Figure 4.4- Gear Shaping
The tool is called gear cutter and resembles in shape the mating gear from the conjugate gear pair, the other gear being the blank. Gear shaping is one of the most versatile of all gear cutting operations used to produce internal gears, external gears, and integral gear-pinion arrangements.
Shaping with a rack-shaped cutter
In the gear shaping with arack-shaped cutter, gear teeth are generated by a cutting tool called a rackshaper. The rack shaper reciprocates parallel to the axis of the gear axis. It moves slowly linearly with thegear blank rotation at the same pitch-cycle velocity: The rack shaper is actually a segment of a rack. Because it is not practical to have more than 6-12 teeth on a rack cutter, the cutter must be disengaged at suitable intervals and returned to the starting point, the gear blank meanwhile remaining fixed.
4.10- MERITS OF GEAR SHAPING PROCESS –
1. Spur helical, rack and internal gears cutting by gear shaping process.
2. Cutter used is universal.
3. Gear cutting by gear shaping is used for medium and large batch of production.
4. Accuracy of gear cutting is better than other process.
4.11- DEMERITS OF GEAR SHAPING PROCESS :–
1. Gear shaping required special types of helical guide for cutting helical gear.
2. Rigidity of gear shaping is less than gear hobbing process.
3. Production rate of gear shaping is less than gear hobbing process.
4.12- GEAR HOBBING PROCESS:--
Hobbing is generally used for external gear cutting. By using special module number of hob different number of teeth obtained in spur and helical gear manufacturing. Worm, worm wheel, straight and involutes gears also generate by hobbing process.
[pic]
Figure 4.5- Gear Hobbing
When hobbing a spur gear, the angle between the hob and gear blank axes is 90° minus the lead angle at the hob threads. For helical gears, the hob is set so that the helix angle of the hob is parallel with the tooth direction of the gear being cut. Additional movement along the tooth length is necessary in order to cut the whole tooth length.
4.13- MERITS OF GEAR HOBBING PROCESS --
1. Gear hobbing process is used for all types of gear cutting. Accept bevel gear.
2. Gear hobbing process maintains accuracy of gear cutting.
3. Production rate is very high in gear hobbing process.
4. Gear hobbing process is suitable for medium and big batch production.
4.14- DEMERITS OF GEAR HOBBING PROCESS --
1. Internal gears not manufacturing by gear hobbing process.
2. In gear hobbing process accuracy decreases during multi start hobbing.
3. Gear hobbing process is not used for cutting gears on flange and soldered shape of work piece.
4.15- GEAR FINISHING PROCESSES --
The gears produced may have some errors. E.g. Pitch circle process, helical errors, Tooth profile errors etc.To eliminate these errors gear finishing is to be done. There are four processes employed for gear finishing
1. GEAR SHAVING:--
Gear finishing operation is carried out by gear shaving cutter by this method index error of gear tooth, helix angle error, profile error can be rectified and also distortion of gear tooth due to heat treatment can be rectified.
2. GEAR GRINDING:--
Gear grinding is generally used to finish a gear tooth profile which has been heat treated to require hardness, other gears has been cutting out on grinding machine. Grinding method use disc type grinding wheel having a shape corresponding to tooth profile by using simple disc wheel the finishing of tooth is done.
[pic]
Figure 4.6- Gear Grinding
3. GEAR LAPPING:--
Gear lapping is done after heat treatment of gears. In this process soft lapping tool grind on surface of gear tooth, by using abrasive compound between tool and surface from which gear finishing is possible.
[pic]
Figure 4.7- Gear Lapping
4. GEAR HONNING:--
Gear finishing by gear honing process is done after shaving and heat treatment of gears from which small burrs remove from gears. This process is used to grind gears with abrasive tools used for special design of high speed machine.
4.16- TYPES OF GEARS:--
1. SPUR GEARS:--The most common of all types, are used to transmit power OR motion between parallel shaft OR between a shaft and a rack. Spur gears have radial teeth uniformly spaced around the outer periphery of their circular shapes, and parallel to the shafts on which they are mounted. Tooth contact between mating spur gears is in a straight line tangent to the pitch circles.
2. HELLICAL GEARS:--They are used to transmit motion between parallel OR crossed shafts OR between a shaft and a rack by meshing teeth that lie along a helix at angle to the shaft. Because of this angle mating of the teeth occurs in such a way that more than one tooth of each gear is always in mesh.
3. CROSSED AXES HELICAL GEARS:Crossed axes helical gears operating with shafts that are non parallel and non intersecting. the action between mating teeth has a welding effect which results in sliding on tooth flanks. These gears have low load carrying capacity, but they are use full where shaft must rotate at an angle to each other.
4. WORM GEARS:--Worm gear sets are usually right angle drives consisting of a worm gear and a worm .worm gear sets are used where the ratio of the speed of the driving member to the speed of the driven member is large, and for a compact right angle drive.
5. INTERNAL GEARS:--Internal gears are used to transmit motion between parallel shafts. Their tooth forms are similar to those of spur and helical gears except that the teeth point inward toward the center of the gear. Common applications for internal gears include rear drives for heavy vehicles, planetary gears, and speed reducing devices. Internal gears are some times used in compact designs, because the center distance between the internal gear and its mating pinion is much smaller than that required for two external gears.
6. RACK AND PINION GEARS:-- A rack is a gear having a pitch circle of finite radius. Its teeth lie along a straight line on a plane. The teeth may be at right angles to the edge of the rack and mesh with a spur gear, or the teeth on the rack may be at some other angle and engage a helical gear.
7. BEVEL GEARS:-- Bevel gears transmit rotary motion between two nonparallel shafts. These shafts are usually at 900 to each other. Straight bevel gears have straight teeth which, if extended inward, would intersect at the axis of the gear. The use of straight bevel gears is generally limited to drive that operate at low speeds and where noise is not important.
□ GEAR SHAPPING PROCESS
← The cutter used in gear shaping is is one type of gear provided with cutting edges.
← The pinion or rack is used as a cutter.
← As shown in fig.gear blank cutter rotates at certain velocity ratio relative to one another and one gear tooth space is generated by one cutter tooth.
← Cutter is provided with rotary plus reciprocating motion and feed motion.
← The reciprocating motion is based on the face width of the gear to be cut.
← When complete depth of space is cut then the cutter is completely withdrawn.
← The gear cutter is done only during upward or downward reciprocating movement of the cuttet.
← The increamental generation of tooth space is obtained as the cutter rotates with the blank.
← IT is seen from fig.
that the gear tooth
generation is done by
increamental cuts
placed nearer to one
another.
[pic]
GEAR SHAPPING BY RACK-TYPE CUTTER
← A rack type cutter is shown in this fig.
← The rack-cutter and gear blank are given motion relative to one another in which the motion of the gear blank is rotary motion and that of rack cutter is longitudinal so that the rack and pinion type combination is produce.
[pic]
• ADVANTAGES OF GEAR SHAPING
← (1)spur ,helical,rack,internel gears can be cut by this process.
← (2)IT is useful for medium and batch production.
← (3)Accuracy of gear cut by this method.
← (4)The rate of production is comparison to forming method.
← (5)Gear production by this process are used in automobiles,machine tools & instruments.
• LIMITATION OF GEAR SHAPING PROCESS
← (1)Special type of helical guide is required to cut helical gears.
← (2)Its rigidity is less in comparison to gear hobbing.
← (3)Production rate is less then gear hobbing.
← (4)Gear is spline can be cut only when sufficient number of grooves and undercuts are there in the job.
EXPERIMENT NO: - 07
THREAD CUTTING
AIM:- TO CUT EXTERNAL THREAD CUT.
[pic]
Figure 5.1- Thread Terminology
5.1- TOOL MATERIAL AND EQUIPMENT:-
1. Raw material: – Bar having 20 mm diameter & 150 mm length.
2. Tools: --
1. Single point “V” tool or square tool if 6 mm pitch is require and two are to be
produced, select the tool 6/2*2 = 6/4 = 1.5 width of cutting edge in mm.
2. Rough cut half round file.
3. Instruments : --
1. Vernier calipers 150 mm ( .02 Lc)
2. Micrometer 0 – 25 mm ( .01 Lc)
4. Other materials: -- cotton waste, oil, chalk.
5.2- Theoretical background: --
Thread cutting: -- Threaded components now produced in large quantities by processes like rolling, grinding, thread milling etc, and by the use of high production threading machine. However, the demand to machine threads by a turner on lathe still exists due to the following reasons.
1) It is advantageous to cut threads on a part of the same lathe on which it is
turned by doing so the threads are cut concentric with other finished surfaces.
2) It maintains and repairs the items where one only OR few parts are required,
it is convenient to produced a duplicate on a lathe than to attempt to get a
replacement.
3) When the threads required are not of a standard type OR when it is not
possible to use taps or dies for the purpose, the lathe can be used very
conveniently.
4) The use of the special m/cs or equipments for the purpose of cutting threads
is not justified due to the number of parts being few in number.
In order to cut a thread, it is necessary to know the form of threads or its c/s
Shape, the diameter of the screw, the pitch and type whether it is single ,
Double, triple or other multiple threads. Before understanding the mechanism
of thread cutting it is necessary to acquaint with some of the terms used in
the process of cutting threads.
Pitch is defined as the distance that a nut would travel in one complete revolution, if the screw is single threaded. Lead is the distance which the nut would travel in one complete revolution, thus the pitch and the lead are the same in a single start thread, but the lead is twice the pitch in a double start thread, as shown in figure.
The depth of a single start thread has a definite relationship to its pitch. The depth increases with pitch, thus reducing the strength of the component. To avoid this difficulty coarse pitch screws are made multiple threaded for quick traverse of the nut without having excessive depth of the thread.
A variety of types and forms of threads are used in practice for different purposes, some of them are METRIC, (BRITISH STANDARD WHITHWORD) BSWPIPE THREADS, (BRITISH STANDARD FINE) BSF, (BRITISH ASSOCIATED THREADS) BA, ETC.The screw threads generally used in INDIA have a 600 included angle and have truncated crests and roots between which there is a clearance. The thread pitch is expressed in millimeter.
The principle of thread cutting operation is shown in figure. Where it is indicated that the carriage is moved by a lead screw by closing the split nut fixed to the carriage apron, the motion from the main spindle is transmitted to the lead screw through a pair of change gears. To cut a screw of the same pitch as the lead screw, the ratio of the speed of the main spindle to that of the lead screw should be 1 to 1. and any two wheel of the same number of teeth could be used to transmit motion from the spindle to the lead screw, if the pitch of the threads to be cut on the job is half that of the lead screw wheel, should twice the pitch of the lead screw be required, the spindle wheel would have to be twice the speed of the driven wheel. When working out change wheels it may be remembered that if a thread to be cut is finer than that on the lead screw the work must receive faster than the lead screw.
The ratio of the driving wheel to the driven wheel is given by the expression,
P1 / P2 = T1 / T2 = N2/N1
Where,
P1= Pitch of the screw to be cut,
P2= Pitch of the lead screw,
T1= Number of teeth on the driving wheel,
T2= Number of teeth on the driven wheel ,
N1= RPM of the spindle,
N2= RPM of the lead screw,
The gear ratio to suit the required pitch of threads can be adjusted by change gears or by quick change gear. Most lathes accepting some of very large size and cheaper ones are equipped with a quick change gear mechanism.When the lathe is not fitted with the mechanism. It is necessary to place required gear in position manually. These change gear serves exactly the same purpose as quick change gears.
Now if it is required to cut a screw having 1.5 mm pitch on a lathe having a lead screw of 6mm pitch, the ratio,
Teeth on driver wheel / Teeth on driven wheel,= Pitch of screw to be cut / Pitch of lead screw = 1.5 / 6 =1 / 4, There for any two gear wheels having a teeth ratio of 1:4 can be used , e.g. gear wheel with 20 teeth on the driver and 80 teeth on the follower can be used.
In cutting multiple threads the procedure to be followed is same as that for single screw threads accept that the lathe must be geared according to the lead instead of the pitch of the single thread. The no. of starts will determine the no. of thread grooves to be cut.
When the first groove is finished, the work is turned one half revolution without disturbing the position of the lead screw of the carriage. To facilitate this it is usual to choose the first driving wheel having the no. of teeth divisible by the no of starts in the screw to be cut, for cutting a triple threaded screw the first driver must have no. of teeth divisible by three.i.e. 30, 60, 90,and so on.Multiple threads can also be cut by setting the top slide parallel with the screw thread being cut so that the slide can be used for adjusting the cut. After the first thread is cut the tool
is moved by means of the top slide feed screw a distance is equal to the pitch of the thread. I.e. one half of the lead for a triple thread and so on.
PRACTICAL NO:-08
PRESENTATION
AIM:- To prepare a presentation on given topics with using power point presentation. Each student have different topics with related to subject M.E.-3.
PRACTICAL NO.:-09
TECHNICAL VISIT
AIM:- To prepare Industrial visit report.(Regarding machining process industries.)
(Explain about your industrial visit with some important point of view like
Company profile, production process, raw material and finish product
Machineries, company’s turnover it’s quality standard etc)
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[pic]
1. This is a speeven to it in the gear blank.
2. 9:*[pic]CJ`OJQJaJ`
h°CJaJj;hìûU[pic]
h°CJ$aJ$h°CJ$OJQJaJ$&h°5?>*[pic]CJ$H*[pic]OJQJ\?^JaJ$#h°5?>*[pic]CJ$OJQJ\?^JaJ$h°5?>*[pic]CJOJQJ\?aJh°5?>*[pic]CJThe hob is worm-type cutter and fluites are cut in its length which provides cutting edge.
3. The hobbing is mainly use to cut external gears.
4. Different number of spur & helical tooth can be cut on the blank using same hob of certain module
5. The worm,worm-wheel,straight and invalute splines can also be generated by this process.
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