lathe.docx

7/29/2019 lathe.docx

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Manufacturing the shaft

Mount the work-piece on the lathe

First take the billet in the necessary dimensions and shear 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 to verify the length we need to reduce by facing. Then clamp the work-

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

centered close the jaws until they just touch the surface of the work. Then twist the work-piece in thejaws to seat it. Next tight the jaws from all 3 chuck key positions to ensure even gripping by the jaws.

Facing both ends

Next operation we need to do is face both ends of the shaft according to the required length. First we

need to mount the cutting tool. Clamp the cutting tool in the tool post and turn 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 left

with a little bump at the center of the face. After clamping the tool post in place, advance the carriage

until the tool is about even with the end of the work-piece. When adjusting the tool use the compoundcrank to advance the tip of the tool until it just touches the end of the work-piece and use the cross feed

crank to back off the tool until it is beyond the diameter of the work-piece. Set the lathe to necessary

speed and turn it on.

Start the facing operation with the roughing cut. Now slowly advance the cross feed crank to move the

tool towards the workpiece. When the tool touches the workpiece it starts to remove metal from the

end. Continue advancing the tool until it reaches the center of the workpiece and thenc rank the tool

back in the opposite direction until it is back past the edge of the workpiece.

It may need to make minimum of 3 passes to get a nice smooth finish across the face. Complete thefacing with the finishing cut. The remove the workpiece form the 3-jaw chuck and measure the length.

Verify the required length need to reduce. Mount the shaft with opposite side and follow the same

operations until the material is removed for required length.

Center drilling

The easier way of doing this is using the work-holding method. After facing we need to mark the live

centers in both ends using the center drill. This is necessary for the turning operation we have to

perform 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 mount the drill chuck into thetailstock and make sure it is firmly seated. Then chose the appropriate center drill bit and mount on the

drill chuck.

Turn on the lathe and set the speed. Use the tailstock crank to advance the drill slowly into the end of

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

Straight turning

Turning is performed to reduce the diameter of the shaft according to the required amount. Since the

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

Since the work piece is relatively longer we need to center drill the free end and use a live center in the

tailstock to support the work-piece. After center drilling the shaft remove the center drill bit and drill

chuck from the tailstock and mount live center to the tail stock and make sure it is seated tightly. Then

advance the live center using tailstock crack until the tip of the live center touches the drilled hole.


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In the drawing the surface roughness is specifically indicated. So choose a single point cutting tool

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

tool is tightly clamped in the tool holder. Adjust the angle of the tool holder so the tool is

approximately perpendicular to the side of the work-piece. Move the carriage until the tip of the tool is

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

the side of the work. Move the carriage to the right until the tip of the tool is just beyond the free end

of the work. We can perform this using hand feed. Since the turning length is less than 120mm we

dont need to use power feed.

Set the lathe into necessary speed and turn on. Turn the carriage hand wheel counter clockwise to

slowly move the carriage towards the headstock. As the tool starts to cut into the metal, maintain a

steady cranking motion to get a nice even cut. Continue advancing the tool towards the headstock until

it is about 3-4 cm away from the chuck jaw since we need to be careful by avoiding the tool from

touching the chuck jaws. Perform several passes until it reaches the required amount of 23mm

diameter. Then mount 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. Follow the same method to turn the remaining

surface. After this you get a shaft which has 23mm diameter.

Step turning

From a one end we need to reduce the diameter by 16mm up to length of 20mm. We need 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. Now determine the 20mm mark up. Advance the cross slide and use

the hand feed to turn down. Since this is such a short distance, we can use hand feed, not power feed.

Taper turning

We can use the compound rest method to machine the taper. Its the cheapest and easiest way o f

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

method. We can use a same single point 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 have

to find the taper angle.

20mm

Tan() =

23mm 16mm 9.9

Now turn workpiece to maximum diameter of

taper. Loosen compound rest lock screws andswivel the compound rest by angle of 9.9.


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Now bring cutting tool near end of workpiece and set a depth of cut of 1 mm.Turn on the lathe and

give feed by moving the compound rest handle. Bring tool to the start point again and set new depth of

cut 1mm more than the previous. Then feed my moving the compound rest handle. Repeat this until

smaller diameter of the steep become 16mm. Finally verify the dimensions of the workpiece.

U cut

Take a multiple cutting point round tool bit and cut the groove needed. Then take a pile and smooth the

edge down to give it a chamfer. With the lathe running at fairly low speed, bring a smooth cut file up

to the end of the workpiece at a 45 angle and apply a little pressure to the file.

Thread cutting

There are 2 things we should determine before we cut a thread which are nominal outside diameter of

the thread and the threads per length. 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. Insert your thread cutting tool in the tool post and adjust the angle of the tool so that it is

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

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

Now set the cross-feed to the original zero position and start up the lathe machine. Make a very

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

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

half-nut lever when you reach the end of the thread. Back off the cross-feed one full turn and crank the

carriage back to the starting point. Repeat above steps until depth has been cut to specified dial depth.

Chamfering

As the finishing move take down the larger diameter end of the shaft and chamfer the edge at an 45angle using a file.

Machine Shut Down

Switch off the lathe machine from the main power and collet all the tools used. Clean all the chips on

the lathe machine using a brush.

Feed direction


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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 at

considerable 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 workpieces 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 workpiece. A secondary function of

cutting fluid is to flush away chips and metal fines from the tool and the workpiece 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 qualities

can 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.


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Case study

Sheering the workpiece

The required length of the workpiece 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 workpiece around 78mm long

allowing margin of error in shearing using hacksaw. After shearing measure the length of the

workpiece using vernier caliper.

lathe.docx

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