WELCOME to

Machine Shop

Central Workshop NATIONAL INSTITUTE OF TECHNOLOGY, ROURKELA-8

GENERAL INSTRUCTIONS TO STUDENTS

1. Students are required to come in proper dress while attending the Workshop

sessional class. They should wear half-shirt, trouser and full shoes. Without full shoes no one will be permitted to enter into the shop.

2. Students are required to come on time as per the timetable. They shall be marked late if they do not turn up within five minutes of the scheduled time. Those comes late, are to take permission from Prof. in-charge to enter into the shop. No one will be allowed if they are late by 15 minutes in any case.

3. Students are required to follow the instructions given by the teacher concerned or instructor strictly. They should remain present in their place of working for the whole class unless otherwise instructed.

4. Students are required to handle only those machine allowed to them by the instructors. Under no circumstances should any student handle machines not assigned to him.

5. Students are required to complete the job within the time allowed to them. They should fill in Workshop Card and hand it over to the instructor concerned each day before entering the shop and collect it before leaving the section. Get ensured that it is signed by the instructor and a grade is given.

One overall grade will be deducted if workshop card is lost. 6. Students are required to clean the machine and return the tools issued to them

after each day work.

7. Students are required to do the job by themselves. Instructors would only help them in difficulty. Students should gather as much information about the machine tools; tools, gauges, processes and other details are possible from the instructors.

8. In case of dispute, misunderstanding or difficulty, they may meet the Prof. in-

charge or Head of the Central Workshop.

9. Assessment shall be done on the basis of attendance, discipline, attitude, quality of jobs done, report and everyday performance.

10. After each class, they are required to submit the record (like lab record) in the subsequent class.

On completion all classes in a shop, all students are required to submit the record, Workshop card and all jobs made by them for evaluation. Each class shop record should consist of the following:

i. Job/ aim with figure. ii. Raw materials required/used. iii. Machine used & other allied machines required and its description. iv. Description about Job holding devices used and other related holding

devises used for the concerned machine. v. Description about the Procedure: vi. Short description about the used and related Tools in the shop.

INSTRUCTION SHEET FOR MACHINE SHOP

Sub: Workshop Practice-I WS-171 0-0-3 2 credits

Workshop Practice-II WS-172 0-0-3 2 credits

JOB: Fabrication of a job involving the following operations: straight turning,

grooving, facing, taper turning and threading.

Raw materials required: Mild Steel Rod (dia. 25 mm.), of length 75 mm.

Machine tools used: Lathe Machine.

Tools required: Facing tool, Grooving tool & Threading tool.

Measuring instruments required : Steel rule, outside caliper

Procedure: i. Get acquainted with Lathe, its operations & have a practice ii. Mounting of the Job in a 3 Jaw chuck on Lathe iii. Centering the job iv. Fixing the cutting tool on tool post v. Setting the speed belt/gear and starting of machine vi. Facing vii. Straight Turning (Roughing and Finishing operations) viii. Chamfering ix) Grooving x)Taper turning xi) Grooving xii)Threading xiii)Drilling xiv) Boring xv) Finishing/greasing/numbering

Reference books: i. Workshop Technology Part-1, W A J Chapman, English Language Book Society. ii. Workshop Technology Vol-II, S.K. Hajra Choudhury, S K Bose and A.K. Hajra Choudhury, Media Promoter & Publisher, Mumbai. iii. Workshop Technology Vol -II, B. S. Raghuwansi , Dhanpat Rai & Co.New Delhi. iv. Production Technology, R.K. Jain, Khanna Publisher.

25 20 20 5 5

20φ 12φ

15φ 20φ

M12 ×1.25 ‘V’ threads

18φ 10φ16φ

15

SAFETY FIRST

Safety Instructions

Before entering the workshop all are bound to adopt the safety-precautions rules strictly to avoid any possible accidents A. Personal safety:

i) Wear tight cloths. ii) Wear covered footwear. Never use half shoes or chappals. iii) Do not run, shout and smoke inside the shop. iv) Never place sharp materials on the shop floor. v) Wear goggles and never wear ring or wrist watch while working vi) Never try to operate a machine if machine tool is not familiar to you. vii) Never clean the chips by bare hands. viii) Long hair and loose clothes are dangerous for working in running machine.

B. Machine Safety: i) Do not start any machines before getting instruction or permission. ii) Never work unguarded machine. iii) Stop immediate the machine hearing unusual sound. iv) Never apply more load beyond the capacity of machine. v) Never start a machine on which ‘under repair’ board is kept. vi) Don’t leave the machine alone while it is in automatic mode.

Practice schedule and Record submission Details

WS-171 &172 L-T-P 0-0-3 2 credits 1st and 2nd Sem. All Branches

Subject: Workshop Practice-I and II 1. A. Practice schedule:

a. Conversant with i) different cutting tools ii) different job holding & tool holding devices iii) measuring instruments iv) Different Operations, etc. b. Conversant with starting and stopping of the machine c. Get acquainted with terms feed, depth of cut, speed, chuck, centering, boring,

facing, grooving, rough & finish turning, taper turning, thread cutting, drilling, chamfering, etc.

B. Record Submission: a) Block diagram showing layout/plan view of machine shop showing different

machines present in the shop. b) Detail drawing of machine indicating different parts c) Drawing block diagram of different operations that will be performed.

2. A. Practice schedule:

a. Cutting of specimen a. Mounting of job on chuck

b. Centering c. Setting the speed belt/gear and starting of machine d. Fixing the cutting tool on tool post B. Record Submission: Description about: a. Procedure for cutting, mounting, centering speed setting, etc b. What are the main parts of a lathe & their specific functions? c. What is the importance of centering and how is it achieved in turning a job on a lathe? 3. A. Practice schedule: a. Facing, Rough turning b. Grooving B. Record Submission: Description about:

a. What are lathe accessories and attachments? Specify their individual functions with sketches.

b. What is meant by cutting speed, feed and depth of cut in turning operations? How are these cutting parameters decided?

c. How is a lathe specified?

4. A. Practice schedule: a. Finish turning, step turning

b. Drilling and boring

B. Record Submission:

Description about: a. What cutting tools are used for the following operations:

i) Rough Turning ii) Drilling operation iii) Chamfering operation iv) Taper turning operation v) Boring operation vii) Thread cutting operation

b. What are the different machining operations that can be performed in a lathe?

5. A. Practice schedule:

a. Taper turning b. Chamfering

B. Record Submission: Description about:

a. What is the difference between straight turning & taper turning as well as rough turning & finish turning? How are they achieved?

b. What are various taper turning methods used in practice? What is the method adopted in your job? Describe the methods with sketches.

c. What are the differences between chamfering, facing, knurling & parting off operations?

6. A. Practice schedule:

e. Gear setting for threading, mounting thread tool, and threading operation d. Finishing e. Numbering/greasing

B. Record Submission: Description about:

a. What is the principle adopted in a lathe for thread cutting? b. What is the specification of the thread that you have cut in your job? What was the

arrangement in the lathe for setting up for such thread cutting? c. Give a conceptual idea with a clear diagram ‘how to protect the operator (eye, hand and body) during cutting operation to avoid any accident.

Taper turning. It is an operation of producing an external conical surface on a workpiece. A small taper may be produced with the help of a forming tool or chamfering tool; but the larger tapers are produced by swiveling the compound rest, as shown, at the required angle or by offsetting the tail stock or by taper turning attachment.

Taper turning.

Note. If D is the larger diameter, d is the smaller diameter and L is the length of taper, as shown in Figure, then

Lathe SETTING FOR SCREW CUTTING It has already been described earlier that it is not necessary that every lathe will be equipped with a quick-change gearbox. Therefore, in such lathes, where such gear box is not provided, a suitable set of gears has to be found out and mounted at the proper position for cutting threads of different pitches. Setting up of lathe For such work includes proper holding of the job, concentric with the lathe centres, Setting of tool at proper height and mounting of the calculated change gears at Proper locations. Figure illustrates the general set-up of the lathe for screw cutting. It is a view from top.

General set up of lathe for screw cutting.

For cutting of threads it is necessary that for every revolution of the spindle (or work)the tool should move parallel to the axis of the job by a distance equal to the lead of the screw to be cut. Obviously, there will be a definite ratio between the longitudinal feed of tool and the speed of the spindle. The desired ratio is obtained with the help of the lead screw by connecting it to the spindle through a train of gears, as shown. Now, the motion from the spindle is transmitted to the reversing gears, then to change gears and finally to the lead screw. On engaging the split half nut the movement of the carriage, and hence of the tool, is guided by the lead screw. This establishes a definite link between the longitudinal tool feed and the job rotation. Normally all the lathe manufacturers provide a complete set of gears and Through their different combinations threads of different pitches can be cut. They also usually provide a table which serves as a guide for selecting a suitable set of change gears for cutting threads of a particular pitch without calculation. For cutting metric threads, a special change gear bracket is to be used in place of the one used for cutting other threads. For calculating the change gears the guiding factor, as already discussed above ,is always the establishment of a definite ratio between spindle speed and longitudinal tool feed. In other words we can say that definite ratio is to be Established between the speeds of spindle and the lead screw as the: latter guides the tool movement.

CUTTING METRIC THREADS ON ENGLISH STANDARD LEAD SCREWS OR VICE VERSA Many a times it may be required to cut metric threads on lathes having British Standard lead screw, i.e., the one having its pitch in inches. In such a case, the following relation will help.

In case of a reverse requirement, i.e., when threads of British Standard pitches are to be cut on a lathe having lead screw of metric pitch, the following relation should be used :

you know that 1 inch is equal to 25.4 mm. So, what is actually done in the above expressions (i) and (ii) is that in the first case we have divided the ratio of the two leads by 25.4 and in the second case we have multiplied this ratio by 25.4. By doing so we have converted the unit of one lead into that of the other in order to have same units for both the leads. Another interesting point to note is that

The reason for this is that the expression in the latter form enables us to find out the change gears very easily, because a gear of 127 teeth is always available with every lathe, whereas there will certainly create a lot of difficulty in calculating the change gears for the reason that it is neither a whole number which can be factorized nor a gear of corresponding number of teeth is available.

Example 6.11. Calculate change gears for cutting R.B. threads of 2 mm pitch on a lathe having lead screw of 6 mm pitch.

Like this we can have a number of solutions and every solution will give the desired result. Example 6.12. Calculate change gears to cut L.H, threads of 1,5 mm. Pitch of the lead screw is 6 mm,

Detail Procedure  1. Be conversant with the machine, sequence of operations to be carried out, read the

drawings carefully, study the manuals of the machine, safety instructions, etc. 2. Issue the tool, specimen, measuring instrument, Job & tool holding devices, and safety

apparatus. Move to the machine officially allotted to you (you are responsible for this machine; don’t allow other one to operate your machine).

3. Mount the job to the job holder (3-jaw chuck). The supplied specimen is of approximately 80 mm. When clamping the job keep approximately 40 mm outside from the jaw.

a. Half tight the job b. Check the eccentricity, and confirm it looking at the end. Adjust the center by

striking it briskly by trial and error. c. Fully tight the job. 4. Set the cutting tool. a. Fix the cutting tool with the tool post and tighten the screws. b. Center the cutting tool point by adjusting the height of the tool by coinciding the

cutting point of the tool with that of dead center of the tailstock. c. Keep the tool inclined leftward for facing. The tool should perpendicular for

turning operation. In principle it should be seen that only cutting point touch the

surface of job while cutting.

d. Tighten the tool by rotating the lever. 5. Set the rpm (N, revolution per minute) of the spindle:

Cutting speed= 1000

DNπ

Where, cutting speed for mild steel is 25-30 m/min, D = diameter of job, N= rpm of spindle to be set

Accordingly, set the two levers at A/B/C and 1/2/3 to get the desired rpm. 6. Start the machine: Pull and give upward movement to the black colored lever switch (under the electrical

control box of carriage) If any problem, to stop the machine, you can follow

a. Give down ward movement to the lever switch to off position (but not to the bottom position, otherwise it will rotate in reverse direction. Middle position is the off position)

b. Push the emergency red button. c. Press the leg brake.

7. Start working : Facing a. Move the carriage (with tool, tool post, compound rest, cross slide) towards the job

by rotating the hand wheel of carriage anticlockwise. b. Move the cross slide (rotating its hand wheel) to touch the cutting point at the outer

corner edge of the job. c. Give feed to cross slide (rotate the cross slide hand wheel) till cutting tip reach the

center of the job (Simultaneously do not rotate the carriage wheel)

d. Take back the cutting tool outward by reversing back the cross slide hand wheel (rotating anticlockwise)

e. Give depth of cut (for facing) by rotating the carriage hand wheel (anticlockwise). (Remember: for turning operation depth of cut is provided by cross slide and feed by carriage movement)

f. Give feed of cut rotating the cross slide hand wheel (clockwise) up to the center g. Repeat the process till the face become full flat and perpendicular to the axis. h. Stop machine. 8. Turning (to get a diameter of 20mm) a. Set the cutting tool perpendicular to the surface of the job. (Unscrew the tool post

lever, position the tool post and tighten it properly) b. Start the machine. c. Just touch the cutting point on the surface of the specimen. d. Give depth of cut (about 0.5mm) to remove the rust portion. e. Cut up to a length of 35.00 - 40.00 mm giving feed by rotating the hand wheel of the

carriage. (Hold the hand wheel by two hand 1800 apart and rotate slowly) f. If the rust is not properly removed, repeat the process once or more giving more depth of cut..

g. Stop the machine. h. Measure the diameter of job accurately

i. Let the initial diameter =Di and final diameter is Df (20 mm) to be achieved.

j. Total depth to cut 2

fi DD −=

k. Now decide in how many number of passes will be required. Accordingly give

depth of cut (by rotating the cross slide hand wheel). Adjust the depth of cut for the

last pass so as to maintain the required diameter also it should be less to get good

surface finish.

l. Stop the machine.

9. Grooving

a. Mark two lines at length 20.0 and 25.0 mm for the area to be grooved.

b. Change the tool for grooving and center it.

c. Fix the tool such that both surface of the tool will not touch the job (only point will touch).

d. Give movement to carriage (feed) and cross slide (depth of cut) to get the groove.

10. Chamfering: a. Inclined the tool so that the tool edge is 450 to the axis of the job. Give

approximately 1 mm depth to chamfer the sharp corner of the job to avoid injury to the operator during holding the job.

b. Stop the machine.

11. Taper turning:

a. Remove the job from the 3-jaw chuck, fix the other end so that groove portion will just outside, center the tool as explained earlier.

b. Turn the job as explain earlier to 20 mm diameter (check: it may happen that the created surface may not coincide with other end surface, so adjust the last depth of cut).

c. Do the facing operation for the end as explained earlier.

d. Mark a line at 25 mm from the end where taper to be started.

e. Turn for 15.0mm diameter, the rest portion ( 25.00 mm from the end)

f. The taper will be done by Compound slide method. So, turn the base of the compound slide as per the taper angle:

⎟⎠⎞

⎜⎝⎛ −

= −

LdD

2tan 1θ , where D= larger diameter, d= smaller diameter, L = axial

length of the taper portion. g. Set the compound rest (check the inclined angle and clamp it.

h. Give depth of cut of about 0.5 mm and give feed by compound slide hand wheel (right to left). Do not move the carriage.

i. Repeat the process; adjust the last depth of cut to get desired taper for the length of 25.00mm.

12. Grooving a. Mark the lengths of 20.0mm and 25.00 mm from the end.

b. Make groove as mentioned earlier.

13. Chamfering a. Turn the end portion (20 mm from end) to get 12.00mm diameter for thread part as

explained earlier.

b. Chamfer the end as explained earlier.

c. Stop machine.

14. Drilling and Boring a. Fix the job in chuck and perfectly center it b. Fix the drill beat on tailstock, position it, start the machine, advance the tailstock mandrel and drill c. Fix the boring bar on tool post, give required depth of cut and enlarge the drilled hole

15. Threading: (Die will not be used) a. Set the gear box as per the chart given on the machine front panel to get the desired

fine thread (M12×1.25 , ie, Outer diameter=12.00 and pitch is 1.25 mm).Remember: If you go for course thread it will be M12×1.75, ie, outer diameter is 12.00 mm and pitch is 1.75mm.

b. Check the rpm of the Job/spindle of machine at slow speed (about 60 rpm). Set the lever accordingly.

c. Set the tool perpendicular to the axis of the job.

d. Start machine.

e. Just touch the tool tip to the surface of the job (to get reference line to give depth of cut for thread height).

f. Position the tool at the end.

g. Give depth of cut about 0.2 mm (2 division).

h. Calculate the depth of thread (that is the total depth to be cut)=0.6134345×pitch. Accordingly, decide how many numbers of passes is required, and for each pass what is the depth of cut.

i. Remember: thread to be cut by automatic feed. So, set the lever in automatic feed (i.e, engage the half-nut)

j. Cutting will start.

k. When the cutting will reach groove, stop machine.

l. Do not disengage the half-nut lever (otherwise thread will be destroyed)

m. Back the tool to the end by reversing the spindle rotation.

n. Give depth of cut and repeat the process till full depth of the thread is obtained.

16. Completion of the Job: a. Finish the job by polishing it by the emery paper. b. Grease the job to avoid rusting. c. Number the job. d. Clean the machine. e. Return the tools. f. Submit the job and Sign the job completion record g. Submit the report within one week.