lathe practical

7/29/2019 Lathe practical

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Part 1- Manufacturing the shaft

1. Mount the work-piece on the latheFirst we took the billet in the necessary dimensions and sheared it using hacksaw to the required length

keeping the allowances for facing the both ends. After shearing the work-piece measure the length of

the shaft using vernire caliper verified the length we need to reduce by facing. Then we clamped the

work-piece tightly in the 3-jaw chuck which was attached to the spindle. In order to get the work

properly centered closed the jaws until they just touch the surface of the work. Then we twisted the

work-piece in the jaws to seat it. Next tight the jaws from all 3 chuck key positions to ensure even

gripping by the jaws.

2. Facing both endsAs the next operation we needed to do is face both ends of the shaft according to the required length.

First we mounted the right cut side facing tool in the tool post and turned the tool post so that the tip of

the cutting tool will meet the end of the work-piece at a slight angle. It is important that the tip of the

cutting tool be right at the centerline of the lathe. If it is too high or too low work-piece will be leftwith a little bump at the center of the face. After clamping the tool post in place, we advanced the

carriage until the tool was about even with the end of the work-piece. When adjusting the tool we used

the compound crank to advance the tip of the tool until it just touches the end of the work-piece and

used the cross feed crank to back off the tool until it was beyond the diameter of the work-piece. Set

the lathe to necessary speed and turned it on.

We started the facing operation with the roughing cut. Then slowly advanced the cross feed crank to

move the tool towards the work-piece. When the tool touches the work-piece it started to remove metal

from the end. We continued advancing the tool until it reaches the center of the work-piece and then

cranked the tool back in the opposite direction until it back past the edge of the work-piece.

Generally it may need to make minimum of 3 passes to get a nice smooth finish across the face.

Complete the facing with the finishing cut. Then we removed the work-piece form the 3-jaw chuck

and measured the length. Verified the required length need to reduce. Mounted the shaft with opposite

side and followed the same operations until the material removed for required length.

3. Center drillingThe easier way of doing this is using the work-holding method. After facing we needed to mark the

live centers in both ends using the center drill. This is necessary for the turning operation we had toperform later on. The alignment between the headstock and tailstock of the lathe enables us to drill

holes that are precisely centered in a cylindrical piece of stock. First mounted the drill-chuck into the

tailstock and make sure it is firmly seated. Then chose the appropriate center drill bit and mount on the

drill chuck.

Turned on the lathe and set the speed. Used the tailstock crank to advance the drill slowly into the end

of the work-piece and continued until the required amount of depth is obtained.

4. Straight turningTurning is performed to reduce the diameter of the shaft according to the required amount. Since the

larger diameter of the shaft is 23mm we needed to step down the diameter of the whole shaft in to

23mm. Since the work piece was relatively longer we needed to center drill the free end and use a live

center in the tailstock to support the work-piece. After center drilling the shaft we removed the center


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drill bit and drill chuck from the tailstock and mounted live center to the tail stock and make sure it is

seated tightly. Then we advanced the live center using tailstock crack until the tip of the live center

touches the drilled hole.

In the drawing the surface roughness is specifically indicated. So chose a curved cutting tool with a

slightly rounded tip. This type of tool should produce a nice smooth finish. Make sure that the tool was

tightly clamped in the tool holder. We adjusted the angle of the tool holder so the tool was

approximately perpendicular to the side of the work-piece. We moved the carriage until the tip of the

tool was near the free end of the work-piece, then advanced the cross slide until the tip of the tool just

touches the side of the work. Moved the carriage to the right until the tip of the tool is just beyond the

free end of the work. We performed this using hand feed. Since the turning length was less than

120mm we didnt need to use power feed.

Set the lathe into necessary speed and turned on. We turned the carriage hand wheel counter clockwise

to slowly moved the carriage towards the headstock. As the tool started to cut into the metal,

maintained a steady cranking motion to get a nice even cut. Continued advancing the tool towards the

headstock until it is about 3-4 cm away from the chuck jaw since we needed to be careful by avoiding

the tool from touching the chuck jaws. We performed several passes until it reached the requiredamount of 23mm diameter. Then we mounted the opposite side of the shaft to perform the turning on

the area which was unable to do due to the clamping of the 3-jaw chuck. We followed the same

method to turn the remaining surface. After this we got a shaft which has 23mm diameter.

5. Step turningFrom a one end we needed to reduce the diameter by 16mm up to length of 20mm. We needed to

perform step down turning.A step is a point at which the diameter of the work-piece changes with no

taper from one diameter to the other. Then we determined the 20mm mark up. Advanced the cross

slide and used the hand feed to turn down. Since this was such a short distance, we used hand feed, notpower feed.

6. Taper turningWe used the compound rest method to machine the taper. Its the cheapest and easiest way of

obtaining steep and short tapers other than offsetting the tailstock method and taper attachment

method. We used the same round nose cutting tool.

The compound rest base is graduated in degrees and can be set at the required angle for taper turning.

With this method, it is necessary to know the included angle of the taper to be machined. First we had

to find the taper angle.

20mm

Tan() =

23mm 16mm 9.9


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Then we turned work-piece to maximum diameter of taper. Loosen compound rest lock screws and

swivel the compound rest by angle of 9.9.

Then brought the cutting tool near end of work-piece and set a depth of cut of 1 mm.Turned on the

lathe and gave feed by moving the compound rest handle. Brought tool to the start point again and set

new depth of cut 1mm more than the previous. Then we fed my moving the compound rest handle. We

repeated this until smaller diameter of the steep become 16mm. Finally we verified the dimensions of

the work-piece.

7. U cutTook a end cutting tool and cut the groove needed. Then took a pile and smoothed the edge down to

give it a chamfer. With the lathe running at fairly low speed, brought a smooth cut file up to the end of

the work-piece at a 45 angle and apply a little pressure to the file.

8. Thread cuttingThere are 2 things we should determine before we cut a thread which are nominal outside diameter of

the thread and the threads per length. We should refer the gear chart and setup the gear train properly.The cutting tool tip must have a 60 angle and use a multiple point cutting tool which is made out of

HSS or carbide. We inserted threading tool in the tool post and adjusted the angle of the tool so that it

was exactly perpendicular to the side of the work. Since this operation dissipates a lot of heat we used

cutting fluid to remove the heat as well as the chips formation.

Then set the cross-feed to the original zero position and started up the lathe machine. We made a very

shallow test cut to make sure that we were actually cutting the intended pitch. After checking the pitch

using a screw pitch gage, advanced the compound feed by smaller amounts on each pass. We

disengaged the half-nut lever when it reached the end of the thread. Back off the cross-feed one full

turn and cranked the carriage back to the starting point. We repeated above steps until depth has been

cut to specified dial depth.

9. ChamferingAs the finishing move take down the larger diameter end of the shaft and chamfer the edge at a 45

angle using a file.

10.Machine Shut DownSwitched off the lathe machine from the main power and we collected all the tools used. We cleaned

all the chips on the lathe machine using a brush.

Feed direction


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Part 2

Safety precautions to follow when working with a lathe machine

1. Before starting any lathe operations, always prepare yourself by rolling up your shirt sleevesand removing your watch, rings, and other jewelry that might become caught while you operate

the machine.

2. Wear goggles or an approved face shield at all times whenever you operate a lathe or when youare near a lathe that is being operated. The lathe can throw off sharp, hot metal chips atconsiderable speed as well as spin off spirals of metal that can be quite hazardous.

3. Wear shoes preferably leather work shoes to protect your feet from sharp metal chips on theshop floor and from tools and chunks of metal that may get dropped.

4. Tie back long hair so it can't get caught in the rotating work. Think about what happens to yourface if your hair gets entangled.

5. Be sure the work area is clear of obstructions that you might fall or trip over. Keep the deckarea around your machine clear of oil or grease to prevent the possibility of slipping or falling

into the machine.

6. Get in the habit of removing the chuck key immediately after use. Some users recommendnever removing your hand from the chuck key when it is in the chuck. The chuck key can be a

lethal projectile if the lathe is started with the chuck key in the chuck.

7. Always use assistance when handling large work-pieces or large chucks.8. Never remove chips with your bare hands. Use a stick or brush, and always stop the machine.9. Always secure power to the machine when you take measurements or make adjustments to the

chuck. Be alert to the location of the cutting tool while you take measurements or make

adjustments.

10.Be attentive, not only to the operation of your machine, but also to events going on around it.Never permit skylarking in the area.

Importance of cutting fluids

The primary function of cutting fluid is cooling and lubrication. A fluid's cooling and

lubrication properties are critical in decreasing tool wear and extending tool life. Cooling and

lubrication are also important in achieving the desired size, finish and shape of the work-piece. A

secondary function of cutting fluid is to flush away chips and metal fines from the tool and the work-

piece interface to prevent a finished surface from becoming marred and also to reduce the occurrence

of built-up edge.

Cooling: Machining operations create heat. This heat must be removed from the process.The chip helps carry away heat from the tool and work piece. Coolant takes heat

from the chips tool, and work piece. To be effective the fluid must be able to

transfer heat very rapidly. The fluid absorbs the heat and carries it away.

Lubrication: In a typical machining operation most of the heat is created by the resistance ofthe work piece atoms to being sheared. The friction of the chip sliding over the

cutting tool face creates the rest. Cutting fluid with good lubrication qualitiescan reduce the friction of the chip sliding over the tool face.


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Benefits of using cutting fluids

1. Improve Part Quality - The use of cutting fluids reduces friction and heat. The removal of theheat prevents the work piece from expanding during the machining operation, which would

cause size variation as well as damage to the materials microstructure.

2. Reduce tooling costs - Proper use of cutting fluids increases tool life, which reduces the toolingcosts. Increased tool life also reduces tool changes and downtime which decreases labor costs.

3. Increase Cutting Speeds and Feeds - Cutting fluids reduce friction and heating a machiningoperation. This allows high speeds and feeds to be used to achieve optimal cutting conditions.

4. Improved Surface Finishes - Effective use of cutting fluids helps remove the chips. Thisprevents the chip from being caught between the tool and work piece where it causes scratches

and a poor surface finish.

5. Rust and Corrosion Prevention - Cutting fluids should protect the tooling, machine, and workpiece against rust and corrosion. Cutting fluids should leave a small residual film that remains

after the water has evaporated.

Cutting tool materials

1. High Carbon Steel - This material is one of the earliest cutting materials used in machining. Itis however now virtually superseded by other materials used in engineering because it starts to

temper at about 220C .So this material is extremely sensitive to heat. This softening process

continues as the temperature rises. As a result cutting using this material for tools is limited to

speeds up to 0.15 m/s for machining mild steel with lots of coolant.

2. High Speed Steel (HSS) - This range of metals contain about 7% carbon, 4% chromium plusadditions of tungsten, vanadium, molybdenum and cobalt. These metals maintain their

hardness at temperature up to about 600, but soften rapidly at higher temperatures.

3. Cemented Carbides -This material usually consists of tungsten carbide or a mixture oftungsten carbide, titanium, or tantalum carbide in powder form, sintered in a matrix of cobalt or

nickel. As this material is expensive and has low rupture strength it is normally made in the

form of tips which are brazed or clamped on a steel shank. The clamped tips are generally used

as throw away inserts.

3-Jaw chuck Vs 4-Jaw chuck

ADVANTAGES

3-JAW CHUCK 4-JAW CHUCK

Self-centering Work can be centered to highprecision

Quick and easy to useCan handle square/rectangular

bar

Can hold hex bar-stock

Can turn work off-center

Slightly more grip on round

stock

DISADVANTAGES

Can't hold square bar-stock Slower to mount work (dial-

indicator required)

Run-out/off-center can't be

easily fixed

Can't hold hex-stockCan't hold irregularly shaped

work

Can't turn off-center


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Part 3 - Case study

1. Sheering the work-pieceThe required length of the work-piece is 75mm. Generally we use 0.01-0.02

inches (0.254-0.508cm) of depth of cut when performing rough facing. So we

need to shear the work-piece around 80mm long allowing margin of error in

shearing using hacksaw and keeping allowance for center drilling. After

shearing measure the length of the work-piece using vernier caliper.

2. Roughly facingNow we need to mark the center by drilling with center drill. Before do that we need to smooth the

surface by facing off the sharp edges created with shearing off. Insert the 3-jaw chuck (which allows

the self-centering) into the spindle and mount the workpice. By using the work holding method and a

right cut side facing tool we can perform facing roughly on both ends. After facing measure the lengthof the work-piece for verification.

3. Center drillingWe need to reduce the diameter using turning. Since the drawing doesnt have

the center mark we have to face off the centers by facing operation. By using

work holding method mark the live center with a center drill bit. Do this for

both ends.

4. Straight turningWe need to reduce the radius of the work-piece by 5mm. After center drilling

remove the drill chuck and mount the live center on the tailstock. Even though

the work piece length is not considerably large we dont want to take a risk. So

I determined to use the support of the live center when turning. By using the

work holding method with live center reduce the diameter by a round nose tool.

Use 0.01 inch of depth of cut if you are not using cutting fluids. Do it for several passes and measure

the diameter using the vernier caliper regularly.

5. FacingNow we need to reduce the excess length of work-piece using facing

operation and faceoff the center marks. Note down the amount of length

need to be reduced. Take a right cut side facing tool and mount it on the toolpost. Now align the tool cutting edge with the center line of the work-piece.

Set up rotation for a lower speed and turn on the lathe. Starting from rough


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face cut gradually reduce the length using several passes and finish off with a smooth surface with the

finishing cut. Use a considerably low depth of cut to obtain a smoother surface.

Unmount the work-piece and measure the length and note down the necessary length to be reduced.

Then mount the workpice in the opposite end. The next step is to zero the tip of the cutting tool to the

face of the work-piece. This position of the handle will serve as a convenient reference point when

reducing the length up to 75mm. Note down the necessary length to be reduced exactly and face it

gradually up to the required length.

6. Step turningWe can do the taper turning as the final operations because after

tapering the shaft end it may lose the grip with the 3-jaw chuck. Our

next task is to reduce the diameter of the shaft using step turning.

Insert a round nose tool to the tool post. Given dimensions in the drawing is not sufficient to identify

the length required to step down. After zeroing the tip of the cutting tool start turning up to required

length. Finish the last passes with finishing cut using low depth of cut.

7. U cutTake an end cutting tool bit and cut the groove needed. This will reduce the stress concentration when

performing taper turning.

8. Taper turningWe can use the compound rest method to machine the taper. Take a

round nose tool fix in to the tool post and adjust the compound rest to

the required angle. In this case the given dimension is not sufficient

to calculate the taper angle.

We must have a mark for the 25mm length where we should finish the tapering when the tool reaches

the 25mm mark. Since we are not tracking the 20mm diameter mark it is necessary to measure the

taper angle accurate as possible.

9. KnurlingKnurling pattern used in the drawing is the diamond pattern. Take the

required knurling tool. Keeping the same work holding method used

in taper turning fix the knurling tool in to the tool post. Press theknurling tool against the larger diameter cylindrical surface from one

end. Mount the tool to apply enough presser to form an impression.


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Turn on the lathe in low speed.Then press the knurling tool against the

rotating steel and slowly increase the pressure until the tool produces a

pattern on the steel. Give the feed by moving the compound rest.

10.ChamferingMount the work-piece in the opposite direction where the larger

diameter end is inside the 3-jaw chuck. Chamfer the lower

diameter end at an angel of 45 using a pile.

11.Thread cuttingSet up the gear trains for necessary settings required for the pitch and the external diameter of the

shaft. Use cutting fluid in this operation. Use a threading tool which has a 60 angle at the tip. Use the

work holding method. Now set the cross-feed to the original zero position and run a test cut to make

sure the pitch and the length. Use a screw pitch gage. Make a several passes until the required thread is

machined.

lathe practical

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