Milling Process

Introduction

WHAT IS MILLING?

Milling is the process of cutting away material by feeding a workpiece past a rotating multiple tooth cutter. The cutting action of the many teeth around the milling cutter provides a fast method of machining. The machined surface may be flat,angular, or curved. The surface may also be milled to any combination of shapes. The machine for holding the workpiece, rotating the cutter, and feeding it is known as the milling machine

Methode Of Milling

1-Up Milling
Up milling is also referred to as conventional milling. The direction of the cutter rotation opposes the feed motion. For example, if the cutter rotates clockwise , the workpiece is fed to the right in up milling.

2-Down Milling
Down milling is also referred to as climb milling. The direction of cutter rotation is same as the feed motion. For example, if the cutter rotates counterclockwise , the workpiece is fed to the right in down milling.

The chip formation in down milling is opposite to the chip formation in up milling. The figure for down milling shows that the cutter tooth is almost parallel to the top surface of the workpiece. The cutter tooth begins to mill the full chip thickness. Then the chip thickness gradually decreases.

3-Other milling operations are shown in the figure

Classification Of Milling

1-Peripheral Milling
In peripheral (or slab) milling, the milled surface is generated by teeth located on the periphery of the cutter body. The axis of cutter rotation is generally in a plane parallel to the workpiece surface to be machined.

2-Face Milling
In face milling, the cutter is mounted on a spindle having an axis of rotation perpendicular to the workpiece surface. The milled surface results from the action of cutting edges located on the periphery and face of the cutter.

3-End Milling
The cutter in end milling generally rotates on an axis vertical to the workpiece. It can be tilted to machine tapered surfaces. Cutting teeth are located on both the end face of the cutter and the periphery of the cutter body.

Turning is the machining operation that produces cylindrical parts. In its basic form, it can be defined as the machining of an external surface:
1-With the workpiece rotating,
2-With a single-point cutting tool, and
3-With the cutting tool feeding parallel to the axis of the workpiece and at a distance that will remove the outer surface of the work.

Taper turning is practically the same, except that the cutter path is at an angle to the work axis. Similarly, in contour turning, the distance of the cutter from the work axis is varied to produce the desired shape.
Even though a single-point tool is specified, this does not exclude multiple-tool setups, which are often employed in turning. In such setups, each tool operates independently as a single-point cutter.

Adjustable cutting factors in turning:
The three primary factors in any basic turning operation are speed, feed, and depth of cut. Other factors such as kind of material and type of tool have a large influence, of course, but these three are the ones the operator can change by adjusting the controls, right at the machine.
Speed: always refers to the spindle and the workpiece. When it is stated in revolutions per minute (rpm) it tells their rotating speed. But the important figure for a particular turning operation is the surface speed, or the speed at which the workpeece material is moving past the cutting tool. It is simply the product of the rotating speed times the circumference (in feet) of the workpiece before the cut is started. It is expressed in surface feet per minute (sfpm), and it refers only to the workpiece. Every different diameter on a workpiece will have a different cutting speed, even though the rotating speed remains the same.
Feed: always refers to the cutting tool, and it is the rate at which the tool advances along its cutting path. On most power-fed lathes, the feed rate is directly related to the spindle speed and is expressed in inches (of tool advance) per revolution ( of the spindle), or ipr. The figure, by the way, is usually much less than an inch and is shown as decimal amount.
Depth of Cut: is practically self explanatory. It is the thickness of the layer being removed from the workpiece or the distance from the uncut surface of the work to the cut surface, expressed in inches. It is important to note, though, that the diameter of the workpiece is reduced by two times the depth of cut because this layer is being removed from both sides of the work.

The turning machines are, of course, every kinds of lathes. Lathes used in manufacturing can be classified as engine, turret, automatics, and numerical control etc.
1-Centre Lathe:
The term Centre Lathe is derived from the fact that in its operation the lathe holds a piece of material between two rigid supports called centres, or by some other device such as a chuck or faceplate which revolves about the centre line of the lathe.
The lathe shown above is a typical example. This machine is usually used in a jobbing (one off) situation or for small batch work where it would be too expensive to specially 'tool up' for just a few items.
The lathe on which you will work is a machine used to cut metal. The spindle carrying the work is rotated whilst a cutting tool, which is supported in a tool post, is made to travel in a certain direction depending on the form of surface required. If the tool moves parallel to the axis of the rotation of the work a cylindrical surface is produced as in Fig 2 (a) , whilst if it moves at right angles to this axis it produces a flat surface as in Fig 2 (b).








The lathe can also be used for the purposes shown in Fig 2c, 2d, 2e and 2f.

2-Turret Lathes:
In a turret lathe, a longitudinally feedable, hexagon turret replaces the tailstock. The turret, on which six tools can be mounted, can be rotated about a vertical axis to bring each tool into operating position, and the entire unit can be moved longitudinally, either annually or by power, to provide feed for the tools. When the turret assembly is backed away from the spindle by means of a capstan wheel, the turret indexes automatically at the end of its movement thus bringing each of the six tools into operating position. The square turret on the cross slide can be rotated manually about a vertical axis to bring each of the four tools into operating position. On most machines, the turret can be moved transversely, either manually or by power, by means of the cross slide, and longitudinally through power or manual operation of the carriage. In most cased, a fixed tool holder also is added to the back end of the cross slide; this often carries a parting tool.

Through these basic features of a turret lathe, a number of tools can be set on the machine and then quickly be brought successively into working position so that a complete part can be machined without the necessity for further adjusting, changing tools, or making measurements.

Single-Spindle Automatic Screw Machines:
There are two common types of single-spindle screw machines, One, an American development and commonly called the turret type (Brown & Sharp), is shown in the following figure. The other is of Swiss origin and is referred to as the swiss type. The Brown & Sharp screw machine is essentially a small automatic turret lathe, designed for bar stock, with the main turret mounted on the cross slide. All motions of the turret, cross slide, spindle, chuck, and stock-feed mechanism are controlled by cams. The turret cam is essentially a program that defines the movement of the turret during a cycle. These machines usually are equipped with an automatic rod feeding magazine that feeds a new length of bar stock into the collect as soon as one rod is completely used.
3-CNC Machines:

Nowadays, more and more Computer Numerical Controlled (CNC) machines are being used in every kinds of manufacturing processes. In a CNC machine, functions like program storage, tool offset and tool compensation, program-editing capability, various degree of computation, and the ability to send and receive data from a variety of sources, including remote locations can be easily realized through on board computer. The computer can store multiple-part programs, recalling them as needed for different parts. A CNC turret lathe in Michigan Technological University is shown in the following picture.

Accessories

The devices employed for holding and supporting the work and the tool on the lathe are called accerssries. They incluedethe device like chucks, driving plat ,dogs,toolholder,andposts,centers,mandrels,jigs and fixtures ,etc the selection of the accessories is governed by the type of the job to be made.

1-Workpiece holding accessories:

A) Chucks:
1-Three-jaw:


A three-jaw chuck is a rotating clamp which uses three or 'jaws', usually interconnected via a scroll gear (scroll plate), to hold onto a tool or work piece. Three-jaw chucks are usually self-centering (as a result of the jaws' meshing with the scroll plate) and are best suited to grip circular or hexagonal cross sections when very fast, reasonably accurate (±.005" TIR) centering is desired. Independent-jaw versions can be obtained.
The image shows a three-jaw chuck and key with one jaw removed and inverted showing the teeth that engage in the scroll plate. The scroll plate is rotated within the chuck body by the key, the scroll engages the teeth on the underside of the jaws which moves the three jaws in unison, to tighten or release the workpiece.

2-Four-jaw:

A four-jaw chuck is similar to a three-jaw chuck, but with four jaws, each of which can be moved independently. This makes them ideal for (a) gripping non-circular cross sections and (b) gripping circular cross sections with extreme precision (when the last few hundredths of a millimeter [or thousandths of an inch] of runout must be manually eliminated). The non-self-centering action of the independent jaws makes centering highly controllable (for an experienced user), but at the expense of speed and ease. Four-jaw chucks are almost never used for tool holding. Four-jaw chucks can be found on lathes and indexing heads.
The image shows a four-jaw chuck with the jaws independently set. The key is used to adjust each jaw separately.

3-Multi jaw:
For special purposes, and also the holding of fragile materials, chucks are available with six or eight jaws. These are invariably of the self-centering design, and are built to very high standards of accuracy.
Two jaw chucks are available and can be used with soft jaws (typically an aluminum alloy) that can be machined to conform to a particular workpiece. Many chucks have removable jaws, which allows the user to replace them with new jaws, specialized jaws, or soft jaws.

4-Self-centering four jaw:
A four jaw chuck with a mechanism for centering the work piece. Sometimes used to refer to chucks where the jaws are moved in interconnected pairs.

5-Magnetic:
Used for holding ferromagnetic work pieces, a magnetic chuck consists of an accurately centered permanent magent face. Electromagnets or permanent magnets are brought into contact with fixed ferrous plates, or 'pole pieces', contained within a housing. These pole pieces are usually flush with the housing surface. The part or 'work piece' to be held forms the closing of the magnetic loop or path, onto those fixed plates, providing a secure anchor for the work piece.

6-Face plates:
For irregular shapes, a face plate can be used. The face plate shown in Fig.2 has racially placed slots which allow the workpiece to clamp to it by means of bolts.

B) lathe centers:

For accurate turning operation, or in cases where the work surface is not truly cylindrical, the workpiece can be turned between centers. This form of work holding is show in fig.3 initially the workpiece has a conical hole drilled at each end to provide location for the lathe centers.

1- Dead center:

A dead center (one that does not turn freely, ie: - dead) may be used to support the workpiece at either the fixed or rotating end of the machine. When used in the fixed position, a dead center produces friction between the workpiece and center, due to the rotation of the workpiece. Lubrication is therefore required between the center and workpiece to prevent friction welding from occurring. Additionally the tip of the center may have an insert of carbide which will reduce the friction slightly and allow for faster speeds. Dead centers may also be fully hardened to prevent damage to the important mating surfaces taper of the taper and to preserve the 60 ° nose taper.

2-Soft center:
Soft centers are identical to dead centers except the nose is deliberately left soft (unhardened) so that it may be readily machined to the correct angle prior to usage. This operation is performed on the headstock center to ensure that the centers axis is aligned with the spindles axis.

3-Live or revolving center:
A live center or revolving center is constructed so that the 60 ° center runs in its own bearings and is used at the non driven or tailstock end of a machine. It allows higher turning speeds without the need for separate lubrication, and also greater clamping pressures. They are used almost exclusively in CNC lathes as well as for general machining operations.
The term live center may also refer to a dead center when mounted in the spindle of the machine, where it is considered to be live by virtue of the spindle bearings rather than its own bearings.

4-Pipe center:
A pipe center has a larger diameter at the 60 ° taper end. This allows the center to be used in the bore of a pipe (or similar workpiece). While a pipe center ensures the workpiece remains concentric, its main advantage is that it supports the workpiece securely. Thin walled material such as pipes easily collapse if excessive pressures are used at the chuck end.

5-Cup center:
The cup center is a variation of the live center and is used in woodworking to support the softer material around the actual center and prevent the material splitting.

6-Drive center:
A drive center is used in the driving end of the machine (headstock). It consists of a dead center surrounded by hardened teeth. These teeth bite into the softer workpiece allowing the workpiece to be driven directly by the center. This allows the full diameter of the workpiece to be machined in a single operation, this contrasts with the usual requirement where a carrier is attached to the workpiece at the driven end. They are often used in woodworking or where softer materials are machined

C) Mandrel:

It is a device for holding and rotation a hollow piece of work that has been previously drilled or bored. The work revolves with the mandrel which is mounted between two centers. The mandrel should be true with accurate centre holes for machining outer surface of the workpiece, concentric with the bore. To avoid distortion and wear, it is made of high carbon steel. For different sizes of holes in workpiece, different mandrels.

D) rests:

When very long job is to be turned between centers on lather, due to its own weight it

provides a springing action and carries a lot of bending moment. The result is that turning tool is spoiled very soon, and may even break sometimes. To avoid this, such jobs are always supported on an attachment known as "steady rest" .this prevent the deflection of the job and at the same time enables the operator to take heavy cuts.fig.5 shows the steady rest and follower rests.

Lathe tool holders are designed to securely and rigidly hold the tool bit at a fixed

angle for properly machining a workpiece (Figure 7-14). Tool holders are designed to work in conjunction with various lathe tool posts, onto which the tool holders are mounted. Tool holders for high speed steel tool bits come in various types for different uses. These tool holders are designed to be used with the standard round tool post that usually is supplied with each engine lathe (Figure 7-15 ). This tool post consists of the post, screw, washer, collar, and rocker, and fits into the T-slot of the compound rest.


Standard tool holders for high-speed steel cutting tools have a square slot made to fit a standard size tool bit shank. Tool bit shanks can be 1/4-inch, 5/16-inch, 3/8-inch, and greater, with all the various sizes being manufactured for all the different lathe manufacturer's tool holder models. Some standard tool holders for steel tool bits are the straight tool holder, right and left offset tool holder, and the zero rake tool holder designed for special carbide tool bits. Other tool holders to fit the standard round tool post include straight, left, and right parting tool holders, knurling tool holders, boring bar tool holders, and specially formed thread cutting tool holders.
The turret tool post (Figure 7-16 ) is a swiveling block that can hold many different tool bits or tool holders. Each cutting tool can quickly be swiveled into cutting position and clamped into place using a quick clamping handle. The turret tool post is used mainly for high-speed production operations.

The heavy-duty or open-sided tool post (Figure 7-17) is used for holding a single carbide-tipped tool bit or tool holder. It is used mainly for very heavy cuts that require a rigid tool holder.


The quick-change tool system (Figure 7-18) consists of a quick-change dovetail tool post with a complete set of matching dovetailed tool holders that can be quickly changed as different lathe operations become necessary. This system has a quick-release knob on the top of the tool post that allows tool changes in less than 5 seconds, which makes this system valuable for production machine shops.

Cutting Tool For Lathes

1-Tool Geometry:
For cutting tools, geometry depends mainly on the properties of the tool material and the work material. The standard terminology is shown in the following figure. For single point tools, the most important angles are the rake angles and the end and side relief angles.
The back rake angle affects the ability of the tool to shear the work material and form the chip. It can be positive or negative. Positive rake angles reduce the cutting forces resulting in smaller deflections of the workpiece, tool holder, and machine. If the back rake angle is too large, the strength of the tool is reduced as well as its capacity to conduct heat. In machining hard work materials, the back rake angle must be small, even negative for carbide and diamond tools. The higher the hardness, the smaller the back rake angle. For high-speed steels, back rake angle is normally chosen in the positive range. There are two basic requirements for thread cutting. An accurately shaped and properly mounted tool is needed because thread cutting is a form-cutting operation. The resulting thread profile is determined by the shape of the tool and its position relative to the workpiece. The second by requirement is that the tool must move longitudinally in a specific relationship to the rotation of the workpiece, because this determines the lead of the thread. This requirement is met through the use of the lead screw and the split unit, which provide positive motion of the carriage relative to the rotation of the spindle. Most lathe operations are done with relatively simple, single-point cutting tools. On right-hand and left-hand turning and facing tools, the cutting takes place on the side of the tool; therefore the side rake angle is of primary importance and deep cuts can be made. On the round-nose turning tools, cutoff tools, finishing tools, and some threading tools, cutting takes place on or near the end of the tool, and the back rake is therefore of importance. Such tools are used with relatively light depths of cut. Because tool materials are expensive, it is desirable to use as little as possible. It is essential, at the same, that the cutting tool be supported in a strong, rigid manner to minimize deflection and possible vibration. Consequently, lathe tools are supported in various types of heavy, forged steel tool holders, as shown in the figure.

The tool bit should be clamped in the tool holder with minimum overhang. Otherwise, tool chatter and a poor surface finish may result. In the use of carbide, ceramic, or coated carbides for mass production work, throwaway inserts are used; these can be purchased in great variety of shapes, geometrics (nose radius, tool angle, and groove geometry), and sizes.

2-Tool angles:
There are three important angles in the construction of a cutting tool rake angle, clearance angle and plan approach angle.


Rake Angle:
Rake angle is the angle between the top face of the tool and the normal to the work surface at the cutting edge. In general, the larger the rake angle, the smaller the cutting force on the tool, since for a given depth of cut the shear plane AB, shown in Figure 4 decreases as rake angle increases. A large rake angle will improve cutting action, but would lead to early tool failure, since the tool wedge angle is relatively weak. A compromise must therefore be made between adequate strength and good cutting action.

Clearance Angle:
Clearance angle is the angle between the flank or front face of the tool and a tangent to the work surface originating at the cutting edge. All cutting tools must have clearance to allow cutting to take place. Clearance should be kept to a minimum, as excessive clearance angle will not improve cutting efficiency and will merely weaken the tool. Typical value for front clearance angle is 6° in external turning.

Plan Profile of Tool:
The plan shape of the tool is often dictated by the shape of the work, but it also has an effect on the tool life and the cutting process. Figure 6 shows two tools, one where a square edge is desired and the other where the steps in the work end with a chamfer or angle. The diagram shows that, for the same depth of cut, the angled tool has a much greater length of cutting edge in contact with the work and thus the load per unit length of the edge is reduced. The angle at which the edge approaches the work should in theory be as large as possible, but if too large, chatter may occur. This angle, known as the Plan Approach Angle, should therefore be as large as possible without causing chatter.

The trailing edge of the tool is ground backwards to give clearance and prevent rubbing and a good general guide is to grind the trailing edge at 90° to the cutting edge. Thus the Trail Angle or Relief Angle will depend upon the approach angle.
A small nose radius on the tool improves the cutting and reduces tool wear. If a sharp point is used it gives poor finish and wears rapidly.

Characteristics of Tool Material

For efficient cutting a tool must have the following properties:
Hot Hardness:
This means the ability to retain its hardness at high temperatures. All cutting operations generate heat, which will affect the tool¡¦s hardness and eventually its ability to cut.

Strength and Resistance to Shock:
At the start of a cut the first bite of the tool into the work results in considerable shock loading on the tool. It must obviously be strong enough to withstand it.

Low Coefficient of Friction:
The tool rubbing against the workpiece and the chip rubbing on the top face of the tool produce heat which must be kept to a minimum.

Tool Materials in Common Use
High Carbon Steel:
Contains 1 - 1.4% carbon with some addition of chromium and tungsten to improve wear resistance. The steel begins to lose its hardness at about 250° C, and is not favoured for modern machining operations where high speeds and heavy cuts are usually employed.

High Speed Steel (H.S.S.):
Steel, which has a hot hardness value of about 600° C, possesses good strength and shock resistant properties. It is commonly used for single point lathe cutting tools and multi point cutting tools such as drills, reamers and milling cutters.

Cemented Carbides:
An extremely hard material made from tungsten powder. Carbide tools are usually used in the form of brazed or clamped tips. High cutting speeds may be used and materials difficult to cut with HSS may be readily machined using carbide tipped tool.

Tool life:
As a general rule the relationship between the tool life and cutting speed is
VTn = C
where;V = cutting speed in m/min T = tool life in minC = a constant
For high-speed steel tools the value of C ranges from 0.14 to 0.1 and for carbide tools the value would be 0.2.

Lathe Related Operations

The lathe, of course, is the basic turning machine. Apart from turning, several other operations can also be performed on a lathe.

1-Straight turning:
Straight turning, sometimes called cylindrical turning, is the process of reducing the work diameter to a specific dimension as the carriage moves the tool along the work. The work is machined on a plane parallel to its axis so that there is no variation in the work diameter throughout the length of the cut. Straight turning usually consists of a roughing cut followed by a finishing cut. When a large amount of material is to be removed, several roughing cuts may need to be taken. The roughing cut should be as heavy as the machine and tool bit can withstand. The finishing cut should be light and made to cut to the specified dimension in just one pass of the tool bit. When using power feed to machine to a specific length, always disengage the feed approximately 1/16-inch away from the desired length dimension, and then finish the cut using hand feed.

2-Boring:
Boring always involves the enlarging of an existing hole, which may have been made by a drill or may be the result of a core in a casting. An equally important, and concurrent, purpose of boring may be to make the hole concentric with the axis of rotation of the workpiece and thus correct any eccentricity that may have resulted from the drill's having drifted off the center line. Concentricity is an important attribute of bored holes. When boring is done in a lathe, the work usually is held in a chuck or on a face plate. Holes may be bored straight, tapered, or to irregular contours. Boring is essentially internal turning while feeding the tool parallel to the rotation axis of the workpiece.

3-Facing:
Facing is the producing of a flat surface as the result of a tool's being fed across the end of the rotating workpiece. Unless the work is held on a mandrel, if both ends of the work are to be faced, it must be turned end for end after the first end is completed and the facing operation repeated. The cutting speed should be determined from the largest diameter of the surface to be faced. Facing may be done either from the outside inward or from the center outward. In either case, the point of the tool must be set exactly at the height of the center of rotation. because the cutting force tends to push the tool away from the work, it is usually desirable to clamp the carriage to the lathe bed during each facing cut to prevent it from moving slightly and thus producing a surface that is not flat. In the facing of casting or other materials that have a hard surface, the depth of the first cut should be sufficient to penetrate the hard material to avoid excessive tool wear.

4-Parting:
Parting is the operation by which one section of a workpiece is severed from the remainder by means of a cutoff tool. Because cutting tools are quite thin and must have considerable overhang, this process is less accurate and more difficult. The tool should be set exactly at the height of the axis of rotation, be kept sharp, have proper clearance angles, and be fed into the workpiece at a proper and uniform feed rate.

5-Threading:
Lathe provided the first method for cutting threads by machines. Although most threads are now produced by other methods, lathes still provide the most versatile and fundamentally simple method. Consequently, they often are used for cutting threads on special workpieces where the configuration or nonstandard size does not permit them to be made by less costly methods. There are two basic requirements for thread cutting. An accurately shaped and properly mounted tool is needed because thread cutting is a form-cutting operation. The resulting thread profile is determined by the shape of the tool and its position relative to the workpiece. The second by requirement is that the tool must move longitudinally in a specific relationship to the rotation of the workpiece, because this determines the lead of the thread. This requirement is met through the use of the lead screw and the split unit, which provide positive motion of the carriage relative to the rotation of the spindle.

6-Knurling:
Knurling is a manufacturing process, typically conducted on a lathe, whereby a visually-attractive diamond-shaped (criss-cross) pattern is cut or rolled into metal. This pattern allows human hands or fingers to get a better grip on the knurled object than would be provided by the originally-smooth metal surface. Occasionally, the knurled pattern is a series of straight ridges or a helix of "straight" ridges rather than the more-usual criss-cross pattern.

7-drilling:
Frequently, holes will need to be drilled using the lathe before other internal operations can be completed, such as boring, reaming, and tapping. Although the lathe is not a drilling machine, time and effort are saved by using the lathe for drilling operations instead of changing the work to another machine. Before drilling the end of a workpiece on the lathe, the end to be drilled must be spotted (center-punched) and then center-drilled so that the drill will start properly and be correctly aligned. The headstock and tailstock spindles should be aligned for all drilling, reaming, and spindles should be aligned for drilling, reaming, and tapping operations in order to produce a true hole and avoid damage to the work and the lathe. The purpose for which the hole is to be drilled will determine the proper size drill to use. That is, the drill size must allow sufficient material for tapping, reaming, and boring if such operations are to follow.
The correct drilling speed usually seems too fast due to the fact that the chuck, being so much larger than the drill, influences the operator's judgment. It is therefore advisable to refer to a suitable table to obtain the recommended drilling speeds for various materials


8-spinning operation:
Metal Spinning is a process by which circles of metal are shaped over mandrels (also called forms) while mounted on a spinning lathe by the application of levered force with various tools. It is performed rotating at high speeds on a manual spinning lathe or performed by CNC controlled automated spinning machines. The flat metal disc is clamped against the mandrel and a series of sweeping motions then evenly transforms the disc around the mandrel into the desired shape.

Metal spinning ranges from an artisan's specialty to the most advantageous way to form round metal parts for commercial applications. Artisans use the process to produce architectural detail, specialty lighting, decorative household goods and urns. Commercial applications range from rocket nose cones to public waste receptacles. Other methods of forming round metal parts include hydro forming, stamping and forging or casting. Hydro forming and stamping generally have a higher fixed cost, but a lower variable cost than metal spinning. Forging or casting have a comparable fixed cost, but generally a higher variable cost. As machinery for commercial applications has improved, parts are being spun with thicker materials in excess of 1" thick steel.
The basic hand metal spinning tool is called a spoon, though many other tools (be they commercially produced, ad hoc, or improvised) can be used to effect varied results. Spinning tools can be made of hardened steel for using with aluminum or solid brass for spinning stainless steel/mild steel. Commercially, rollers mounted on the end of levers are generally used to form the material down to the mandrel in both hand spinning and CNC metal spinning. Rollers vary in diameter and thickness depending the intended use. The wider the roller the smoother the surface of the spinning, the thinner rollers can be used to form smaller radii.
The mandrel/chuck can be made from wood, steel alloys, or synthetic materials. The choice of material is dictated by the hardness of the material to be spun and by how many times the tool is expected to be used.
Metal spinning can be accomplished using a wide variety of materials from soft tempered aluminum and copper to structural plate steel and stainless steels.
The manual lathe in question is sometimes a regular woodworking lathe, although a Wilson lathe is the most common manual spinning lathe in the UK. The mandrel having been formed from wood on the lathe or steel chuck machined on a CNC lathe previous to mounting on the metal stock. Cutting of the metal is done by hand held cutters, often foot long hollow bars with tool steel shaped/sharpened files attached. This is dangerous and should only be done by skilled tradesmen. All stock sizing is done prior to the spinning.

9-Reaming On Tthe Lathe:
Reamers are used to finish drilled holes or bores quickly and accurately to a specified diameter. When a hole is to be reamed, it must first be drilled or bored to within 0.004 to 0.012 inch of the finished size since the reamer is not designed to remove much material.
The hole to be reamed with a machine reamer must be drilled or bored to within 0.012 inch of the finished size so that the machine reamer will only have to remove the cutter bit marks.
The workpiece is mounted in a chuck at the headstock spindle and the reamer is supported by the tailstock in one of the methods described for holding a twist drill in the tailstock.
The lathe speed for machine reaming should be approximately one-half that used for drilling.
The hole to be reamed by hand must be within 0.005 inch of the required finished size.
The workpiece is mounted to the headstock spindle in a chuck and the headstock spindle is locked after the piece is accurately setup The hand reamer is mounted in an adjustable tap and reamer wrench and supported with the tailstock center. As the wrench is revolved by hand, the hand reamer is fed into the hole simultaneously by turning the tailstock handwheel.
The reamer should be withdrawn from the hole carefully, turning it in the same direction as when reaming. Never turn a reamer backward.

Safety Equipments

Although wood turning on a lathe is probably statistically safer than using other woodworking tools and machines, it has some very specific safety rules that should be followed. If adherence to these safety rules can be enforced from the outset until they become habit, your wood turning will consistently be a safe and enjoyable experience.
Safety Glasses: As with all woodworking, safety glasses are the most important piece of safety equipment. There are numerous styles of safety glasses. Try out the many styles that your woodworking supplier offers, and find a pair that you'll be comfortable wearing. Be certain that the pair you choose incorporates impact resistant lenses and side screens to protect against debris created by your power tools.
Face Shield: A face shield is a good idea when wood turning, as chips tend to fly in any direction. A clear, impact resistant full-face shield will keep these flying chips and debris out of your face, helping you to avoid distraction when turning.
Proper Attire: When wood turning, proper attire is of the utmost concern. It is adviseable to wear long pants and a long sleeved shirt to keep flying chips and debris at bay. However, you should wearing avoid loose-fitting clothing, to prevent the excess cloth from becoming entangled in the machine. Also, when wood turning, a woodworker's apron is a good idea. This will also help keep flying wood chips away from your body.
Respirators: When turning some woods, particularly fine imported woods such as mahogany or rosewood, it is advisable to wear a dust mask or even a respirator, as the fine dust generated by turning these woods can cause irritation to the lungs and mucous membranes. Prolonged exposure to such dust may cause some long-term effects.
Always Use the Tool Rest: When wood turning, never free-hand a tool into the turning stock. At the very minimum, this can cause tear-out, which can ruin your hard-earned efforts and turn a fine wood turning into firewood immediately. Even worse, free-handing can cause the tool to be ripped out of your hands. A flying, sharp cutting tool is a recipe for disaster.

Types of Gears

1-Angular Bevel Gears:

These are bevel gears whose shafts are set at an angle other than 90 degrees. They are useful when the direction of a shaft's rotation needs to be changed. Using gears of differing numbers of teeth can change the speed of rotation.

These gears permit minor adjustment of gears during assembly and allow for some displacement due to deflection under operating loads without concentrating the load on the end of the tooth. For reliable performance, Gears must be pinned to shaft with a dowel or taper pin.

The bevel gears find its application in locomotives, marine applications, automobiles, printing presses, cooling towers, power plants, steel plants, defence and also in railway track inspection machine. They are important components on all current rotorcraft drive system.

2-Bevel Gears

They connect intersecting axes and come in several types. The pitch surface of bevel gears is a cone. They are useful when the direction of a shaft's rotation needs to be changed. Using gears of differing numbers of teeth can change the speed of rotation. They are usually mounted on shafts that are 90 degrees apart, but can be designed to work at other angles as well.

These gears permit minor adjustment during assembly and allow for some displacement due to deflection under operating loads without concentrating the load on the end of the tooth. For reliable performance, Gears must be pinned to shaft with a dowel or taper pin. Bevel gear sets consist of two gears of different pitch diameter that yield ratios greater than 1:1.

Types

The teeth on bevel gears can be straight, spiral or bevel. In straight bevel gears teeth have no helix angles. They either have equal size gears with 90 degrees shaft angle or a shaft angle other than 90 degrees. Straight bevel angle can also be with one gear flat with a pitch angle of 90 degrees. In straight when each tooth engages it impacts the corresponding tooth and simply curving the gear teeth can solve the problem. Spiral bevel gears have spiral angles, which gives performance improvements. The contact between the teeth starts at one end of the gear and then spreads across the whole tooth. In both the bevel types of gears the shaft must be perpendicular to each other and must be in the same plane. The hypoid bevel gears can engage with the axes in different planes. This is used in many car differentials. The ring gear of the differential and the input pinion gear are both hypoid. This allows input pinion to be mounted lower than the axis of the ring gear. Hypoid gears are stronger, operate more quietly and can be used for higher reduction ratios. They also have sliding action along the teeth, potentially reducing efficiency.

Applications

A good example of bevel gears is seen as the main mechanism for a hand drill. As the handle of the drill is turned in a vertical direction, the bevel gears change the rotation of the chuck to a horizontal rotation. The bevel gears in a hand drill have the added advantage of increasing the speed of rotation of the chuck and this makes it possible to drill a range of materials. The bevel gears find its application in locomotives, marine applications, automobiles, printing presses, cooling towers, power plants, steel plants, defence and also in railway track inspection machine. They are important components on all current rotorcraft drive system.

Spiral bevel gears are important components on all current rotorcraft drive systems. These components are required to operate at high speeds, high loads, and for an extremely large number of load cycles. In this application, spiral bevel gears are used to redirect the shaft from the horizontal gas turbine engine to the vertical rotor.

3-Crown Wheel and Pinion

A crown wheel is a wheel with cogs or teeth set at right angles to its plane and the pinion is a small cogwheel that meshes with the crown wheel. Crown wheel and pinion have excellent heat distortion control, high strength, wear resistance property and noiseless and vibration free operation. They are made of fine-grained steel billet.

The pinion thread is specially made on the thread grinder to ensure proper fitting. Tooth contact of a crown pinion is inspected on a Gleason machine at regular intervals of time for uniform hardness and adequate case depth. They are checked thoroughly for high spots because this ensures premature failure and noise-free operation. The crown wheel & pinion are paired and checked for centralized tooth bearing and desired proximity. An elliptoid contact pattern is ensured between the crown wheel and pinion.

In a machine, when any torque is applied to the drive unit, the tendency is for the crown wheel and pinion to be forced into or out of mesh by the sliding contact. The amount of pre-load on the bearings determines how much torque can be transmitted without allowing end float, which cause the meshing of the gears to become incorrect.

Application

Crown wheel & pinion are used widely in automotive industries. They are one of the most stress prone parts of a vehicle. They are used in automobiles to maintain forward motion. To maintain forward motion both output drive shaft sides covers are removed and the pinion and crown wheel are swapped completely with differential.

4-Crown Wheel

A crown wheel is a wheel with cogs or teeth set at right angles to its plane. The internal diameter of a crown wheel is ground by holding the component in pitch like chucks to ensure accuracy of the finished gear.

As a result of the development of "flat" crown wheels it has become possible to construct a special gearbox. IHC has used these new gearwheels to produce a prototype of a continuously variable speed gearbox.

Applications

Crown wheels are used in motorcycle automotive gearboxes. It is also used in mechanical clocks. The clock consists of a crown wheel, rotated by a falling weight, whose teeth drive the pallets of a verge backward and forward. This verge is connected to an arm with a hammer on the end that struck the bell.

5-Differential Gears

Differential gears link two shafts with a covering, forcing the total of the rotational angles of the shafts to be the same as the rotational angles of the covering. Arrangement of the system is done in such a way that one axle turns faster than the other.

When a differential gear is meshed with the other gear then the highly efficient torque is applied from the differential side gears to the axle shaft. When torque level decreases then the gear separating forces also decreases allowing the axle shaft to rotate independently. Differential gears can add or subtract the movement of two inputs. In practical terms, they will turn the number of revolutions proportional to the movements of both inputs. They are used to convert the lengthwise flow of power from the engine through the clutches, transmissions, and propeller shafts into a right-angle direction. This change allows the engine power to turn the wheels.

In the differential gears there are two coaxial gears, the pinions and the turntable. Pinions are mounted on intermediate shafts and these shafts are connected to a fixed carrier called the turntable. The differential gears are lubricated with a fluid that absorbs heat and increases the life and performance of the gears as well as the wheel. Regular driving subjects the fluid to high heat that breaks the fluid at a later stage. This results in the contact of two metals, which eventually increases the heat and prevents the gear from turning the car's wheel. So, the fluid should be properly checked in regular intervals.

Types of Differential Gears:

There are two designs of differential gears, hypoid and spiral.

a)Spiral Differential:In spiral differential the pinion gears contacts the ring gears at its centerline.

b)Hypoid Gear: In the hypoid the pinion gear contacts the ring gear below the centerline. The size of pinion gear in hypoid differential is much smaller and the contact ratio is high, comparatively hypoid differential is much stronger than the spiral differential.

Applications

Differential gears in automobiles are the most common application of these gears. When the car is moving in a straight line, there is no movement of the differential gear with respect to its axis but when the car takes a turn then these gears help two wheels of the car to rotate differentially with respect to each other. When one wheel is stationary then the counterpart wheel rotates at twice of its expected speed.

6-External Gear

These are the most often used and the simplest gear system with cylindrical gears with straight teeth parallel to the axis. They are used for transmitting rotary motion between parallel shafts. When a smaller gear called the pinion, drives the larger gear called the wheel, also having external teeth, the corresponding driving and driven shafts rotate in opposite direction. The two gear surfaces come into contact once and so they are noisy at high speed.

External gears are generated with a tool moving forward towards the component axis. Internal gear cutter with very small diameter and few teeth is used for the production of external gear. External gears are widely used in various industrial sectors like coal industry, mining, steel plant, paper industry, and many more.

7-Fine Pitch Gears

They are widely used in aerospace, nuclear and medical industries. They are available in plastic, steel, stainless steel and brass. They are used largely to transmit motion rather than power. They have high tooth strength.

Fine pitch gears are inspected by functional testing on a variable-center-distance fixture. They do not lend themselves to the kind of detailed tooth measurements because of their small dimensions.

Fine pitch gear is used widely in oil industry and for automotive transmission.

8-Girth Gears

The girth gear has been preferred over the gearless drives due to their lower initial cost, simplicity to install, operate and maintain. In the past many years girth gears have gone through enormous improvements. They have high efficiency and the overall life of these gears depends upon proper lubrication and alignment. They are high quality, high precision component. The capital cost of girth gears is lower than others and they take less time to install. They are physically big and due to this they are unable to store for longer periods of time.

Girth gear materials have made several changes on their own. Casting is enhanced using full ring risering techniques. Simulation programs are installed for verification of proper solidification. New materials are used with an added advantage of increase in hardness and therefore increased ratings.

The girth gear is the heart of most mills and kiln drive system. They can't be used in spare parts inventory. They are also used in steel industry, sugar industry, paper and pulp industry

9-Hardened and Ground Gears

Hardened and ground gear has two types of shaft arrangements. They can be parallel shaft type or hollow shaft type. Hardened and ground gear delivers a maximum hob rotation and table rotation with excellent machining accuracy. Hardened ground gear provide a noise free and long term operation. They are characterized by high output, easy operation and precise machining. They offer rigidity, strength and high resistance to shock load. They are available in a wide range of sizes and gear ratios.Hardened gears are used in several essential machine tools like wheels, bedways, etc. and are widely used in the aerospace industry.

10-Helical Bevel Gears

Helical bevel gear is a toothed gear in angular design. The input side is provided with a motor flange or a free input shaft and the output side are provided with a free shaft end or a hollow shaft. Helical bevel gears are fitted with flanges of various sizes. Reciprocating tools cuts them. The advantages of helical bevel gears are high efficiency and low reduction rate. The use of helical bevel gear saves energy and cost. Helical bevel gears are manufactured by an alloyed case hardening steel. The gear material is given an extremely strong, homogeneous structure. They can replace worm gears in a variety of applications, particularly in modular machinery. They are also used as storage and retrieval unit. They are commonly used in modern differentials.

11-Helical Gears

Helical gears connect parallel shifts but the involute teeth are cut at an angle to the axis of rotation. Two mating helical gears must have equal helix angle but opposite hand. They run smoother and more quietly. They have higher load capacity, are more expensive to manufacture and create axial thrust.

Helical gears can be used to mesh two shafts that are not parallel and can also be used in a crossed gear mesh connecting two perpendicular shafts. They have longer and strong teeth. They can carry heavy load because of the greater surface contact with the teeth. The efficiency is also reduced because of longer surface contact. The gearing is quieter with less vibration.

Gear Configuration

They can be manufactured in both right-handed and left-handed configurations with a helix angle to transmit motion and power between non-intersecting shafts that are parallel or at 90 degrees to each other. For shaft at 90 degrees, the same helix angles are used and the tooth contact area of the gear is very small. If the angle of gear teeth is correct, they can be mounted on perpendicular shaft by adjusting the rotating angle by 90 degrees. The inclination of the teeth generates an axial force. As the angle of inclination increases the axial force also increases. Thrust bearings can counter these forces.

Applications

These are highly used in transmission because they are quieter even at higher speed and are durable. The other possible applications of helical gears are in textile industry, blowers, feeders, rubber and plastic industry, sand mullers, screen, sugar industry, rolling mills, food industry, elevators, conveyors, cutters, clay working machinery, compressors, cane knives and in oil industry.

Disadvantage

A disadvantage of helical gear is the resultant thrust along the axis of the gear, which needs to be accomodated by appropriate thrust bearings. This can be overcome by the use of double helical gears by having teeth with a 'v' shape.

12-Herringbone Gears

They conduct power and motion between non-intersecting, parallel axis that may or may not have center groove with each group making two opposite helices. The two helix angle come together in the center of the gear face to form a 'V'. in these gears the end thrust forces cancel themselves out. Its difficult to cut this type of gear but its made easier by machining a groove in the face at the point of the apex of the 'V' creating a break in the middle of the herringbone gear teeth. They do not have any separating groove between the mirrored halves.
Action is equal in force and friction on both gears and all bearings. Herringbone gear also allow for the use of larger diameter shaft for the same volumetric displacement and higher differential pressure capability.
The most common application is in power transmission. They utilize curved teeth for efficient, high capacity power transmission. This offers reduced pulsation due to which they are highly used for extrusion and polymerization. Herringbone gears are mostly used on heavy machinery.

13-Master Gear

They offer high precision, low volume productions. They are used for composite testing of production components. They have high speed, quiet operation, longer life and greater efficiency.
The most common applications are as setting masters and rolling masters for inspection and production applications. They are used to determine the accuracy of work gears. When master gears and work gears are rolled together on rolling fixtures dimensional variations are determined by various indicators, charts or other indicating devices. Master Gears are also used in aerospace and automotive industry.

14-Mill Header

Mill headers find heavy usage in industrial sectors as an essential part of various vehicles and machines. They are used in various industrial sectors including coal and mining, oil exploration, paper mining, chemical industries, cement plant industry, sugar mill and many more. In industrial sectors these gears are used as an important part of conveyors, cranes, elevators, separators and kilns because they offer high power-density and modularity.

15-Non-Involute Gears

Non-involute gears have reduced specific sliding. Reduced gear sliding has an affect on low speed meshes, where sliding losses predominate. The efficiency of these gears is also increased by the use of less viscous oil.

The tooth profile geometry is uniquely defined by the arc shaped path of contact. The gears manufactured by the same rack cutter have the concave convex mesh. The result of enlarged reduced radius of curvature has as a consequence reduced pressure and better lubrication conditions. The geometry of non-involute gear tooth provides substantially higher capacity than any other gearing.

The disadvantages of the non-involute gearing are lower transverse contact ratio and great sensitivity to the center distance accuracy.

16-Pinion Gears

It is a small cogwheel. The teeth fit into a larger gear wheel. Rotational motion is converted into linear motion when the pinion turns and moves the rack. Pinion gears are engineered to be the best gears.

Pinion gear system involves the use of a small round gear called pinion and a large flat gear called rack, more the number of teeth in the pinion gear, more is the speed of rotation. Pinion with smaller number of teeth produces more torque. Pinion is attached to the motor shaft with glue. Rotation of pinion is done by rotation of pinion about a fixed center that helps the rack to move in the straight line. If the rack is moved and the pinion rotates then the center of the pinion moves taking along the pinion with it.