The specification plate on the lathe in the illustrations.
Select a lathe suitable for your project. Bench top lathes can be ideal for turning
small projects like ink pens and yo-yos, larger machines may be used
for making spindles used in furniture and handrail styles. Here are some
differences in wood lathe specifications:
Bed length is the distance between centers, or the maximum length of the stock that can be turned.
Swing is the term used to describe the largest diameter stock that can be turned.
Horsepower
is the amount of torque the lathe motor develops, which in turn will
determine how heavy an item can be turned without overloading this
critical component.
RPMs are the revolutions per minute the stock can be turned. Here,
note that most, if not all lathes have variable speed capabilities. A
lathe with a very low speed range allows the user to start a piece of
odd shaped, unbalanced stock without excessive vibration, and high speed
machines can speed the work while making obtaining a fine, smooth
finish easier to achieve.
Weight and composition. Heavier machines with cast iron beds and
steel frames offer a good, solid work platform, but can be difficult to
move if you are operating it in a crowded workshop where you will be
storing it when it is not in use.
2
Choose the lathe operation you are going to begin with. A simple task might be to turn a square or irregularly shaped piece of wood to a truecylindrical shape, often the first step to forming a spindle or other round item.
3
Assortment of turning tools, including gouge, parting tool, larger gouge, and skew chisel, from left to right.
Select the correct cutting tools for your objective.
Lathe tools are called knives or chisels, sometimes interchangeably.
They feature long, round, curved handles to afford a solid grip and
sufficient leverage to enable the turner to control the cutting edge
accurately with minimal fatigue. Common wood chisels simply are too short and are ill-designed for this purpose. Here are a few of the many types turning tools you may find:
A knurling gouge, used for cutting knurls or “vee” shapes into the work piece efficiently.
Gouges. These usually have specially shaped cutting edges for performing particular cuts, such as bowl gouges, with concave, curved cutting edges to form the smooth, curved surface of a bowl, or vee, or knurling gouges for cutting grooves or knurls in wooden spindles.
Scrapers. These are often flat or slightly curved chisels for removing wood from flat or cylindrical shapes, or for roughing out a shape.
A parting tool, used to cut the work piece through, or part it.
Parting tools. These are thin, vee tipped tools for cutting off work pieces.
Spoon cutters have a spoon shaped cutting edge and are also often used for shaping bowls.
Other tools you may encounter are skew chisels, fluted gouges, spindle gouges, and nose chisels.
4
Learn the components of your lathe. A basic wood lathe consists of a bed, headstock, tailstock, and tool rest. Here are the functions of each of these parts.
This headstock has a number 2 Morse taper bore to hold the spur center.
The headstock consists of the drive train, including the motor, pulleys,
belts, and spindle, and for a right handed turner, will be located on
the left end of the lathe. Mounted on the end of the headstock facing
the tailstock is the spindle and the spur center or for face turning
such as bowls and plates, or other flat or face work, the face plate assembly.
This is the tailstock, the crank on the end forces the cup center into the end of the work piece.
The tail stock is the free spinning end of the lathe, and has the tailstock spindle and the cup center, as well as a hand-wheel or other feature for clamping or securing the work piece between the lathe centers.
This is a view of the tool rest. It is a pretty massive steel assembly, to support the tool while cutting.
The tool rest is similar to a mechanical arm with a metal guide bar to
support the chisel or knife used for turning the work piece. It usually
can be adjusted by sliding the length of the bed at its base, with an
intermediate arm that can swing from a parallel to a perpendicular
position in relation to the lathe bed, and the upper arm, which holds
the actual tool rest bar. This assembly has as many as three swivel joints, all of which tighten with a setscrew or clamp to keep it secure while turning is in progress.
5
Read your owner's manual
before proceeding with actual lathe work for specific instructions,
features and detailed safety instructions. Keep your owner's manual
handy for reference if you decide to purchase accessories for your
particular lathe, for maintenance instructions, and for reference to
capacities and specifications for your machine.
6
Select a suitable piece of wood for your project.
For a beginner, using a softwood like southern yellow pine, lodge-pole
pine, or balsam fir may be a good idea. Look for a piece with fairly
straight grain, and few, tight, knots. Never turn a split piece of stock, or one with loose knots, these may separate during turning, and become projectiles traveling at a significant speed.
7
Square the stock. For example, if you are going to begin with a piece of 2X4 lumber, rip it to a nominally square shape, such as 2X2. You can then chamfer, or bevel the square corners, effectively creating an octagonal piece, which will reduce the amount of wood that must be removed to reach your desired cylindrical shape.
8
Cut the stock to the desired length.
For a beginner, starting with a relatively short length, less than 2
foot long for an intermediate, or medium sized lathe, is a good choice.
Longer work pieces are difficult to true, and maintaining a uniform
diameter along the length of a longer piece can take a lot of work.
9
Mark the center of each end of your stock, and position it between the lathe centers.
Assuming the tailstock is not locked in position, slide this until it
pushes the cup center into the tail end of your work piece. Using the
hand crank, tighten the tailstock spindle so that it pushes the stock
into the spur center, mounted on the headstock spindle. Make sure the
work piece is securely held, and all clamps are tightened, otherwise,
the work piece may fly off the lathe while you are turning.
10
Here the tool rest is in position to turn this work piece.
Position the tool rest parallel to the length of the work piece, keeping it far enough back to allow the work piece to rotate without hitting it, but as close as possible.
A good working distance is about 3/4 of an inch. Remember, the closer
the tool rest is to the turning work piece, the more leverage and better
control you will have with your knife (chisel).
11
Free spin, or hand turn the work piece to make sure it doesn't hit the tool rest.
It is a good practice to always turn a work piece by hand before
turning the lathe on, making sure it has sufficient clearance.
12
Choose the knife you will use for the turning operation. A roughing gouge
is a good choice for beginning to turn an irregular or square work
piece down to a round shape. Practice holding the knife on the tool
rest, using your left (again, for right handed persons) hand on the
metal blade behind the tool rest, and your right near the end of the
handle. Keeping your elbows in, and braced against your body will give you better control of the tool.
13
Here you can see the speed control, set on low, and the on/off switch. Notice the switch is keyed, so the machine can be disabled when not in use.
Turn the lathe on, making sure it is at the lowest speed setting. Place the cutting edge of the tool on the rest, keeping clear of the rotating work piece, check your grip, and slowly begin easing
it toward the work piece. You want to move in toward it perpendicular
to the work piece, until the cutting edge just touches the wood. Forcing
it or moving too quickly will cause the tool to jam into the wood, and
it will either break off, or you will lose your grip on the tool if the
lathe doesn't stall out. This is one of the most dangerous steps in
beginning turning.
14
Feel the resistance of the cutting edge and watch the size of the chips being cut from the work piece. When truing, you will want to cut small chips, less than 1/4 of an inch in length.
15
Begin moving the cutting edge parallel to the rotation of the work piece, continuing to make a light cut along its length. When using a roughing gouge or similar tool, you can cant,
or pitch the tool edge so chips are thrown at an angle from the work
piece, so you do not become covered with them while you turn. Twist the
tool slightly and observe the flight path of the chips to adjust it so
they fly away from you to your right or left.
16
Continue pushing the tool into the stock gradually, in passes, so that you remove a roughly equal amount of wood with each pass. This will eventually cut away the angular corners, leaving your work piece round, and with practice, cylindrical in shape.
17
Stop the lathe
frequently when you are just beginning, to check your progress, look for
stress cracks in the wood, and clear debris which may begin to
accumulate on the lathe bed. You may want to use a pair of calipers to check the diameter of your work piece along its length so you finish with the desired diameter.
18
Smooth the finished
round work piece by increasing your lathe speed, and holding your
cutting tool so it barely contacts the wood, then moving it slowly along
the work piece’s length. The slower your tool movement, and finer, or lighter the cut, the smoother the finished cut will be.
19
Sand the work piece when you are finished cutting if desired.
You can sand the stock by hand while it is turning if you use caution.
Turn the lathe off, and swing the tool rest out of the way, then select a
suitable grit and type of sandpaper for this process. Turn the lathe
back on, and hold the paper lightly against the wood, moving it back and
forth to prevent removing too much wood from one area of the work
piece.
Turning is a form of machining, a
material removal process, which is used to create
rotational parts by cutting away unwanted material. The
turning process requires a turning machine or lathe,
workpiece,
fixture, and cutting tool. The workpiece is a
piece of pre-shaped material that is secured to the
fixture, which itself is attached to the turning
machine, and allowed to rotate at high speeds. The
cutter is typically a single-point cutting tool that is
also secured in the machine, although some operations
make use of multi-point tools. The cutting tool feeds
into the rotating workpiece and cuts away material in
the form of small chips to create the desired shape.
Turning is used to produce
rotational, typically axi-symmetric, parts that have
many features, such as holes, grooves, threads, tapers,
various diameter steps, and even contoured surfaces.
Parts that are fabricated completely through turning
often include components that are used in limited
quantities, perhaps for prototypes, such as custom
designed shafts and fasteners. Turning is also commonly
used as a secondary process to add or refine features on
parts that were manufactured using a different process.
Due to the high tolerances and surface finishes that
turning can offer, it is ideal for adding precision
rotational features to a part whose basic shape has
already been formed.
Ceramics Composites Lead Nickel Tin Titanium Elastomer Thermoplastics Thermosets
Surface finish - Ra:
16 - 125 μin
2 - 250 μin
Tolerance:
± 0.001 in.
± 0.0002 in.
Max wall thickness:
0.02 - 2.5 in.
0.02 - 80 in.
Quantity:
1 - 1000
1 - 1000000
Lead time:
Days
Hours
Advantages:
All materials compatible
Very good tolerances
Short lead times
Disadvantages:
Limited to rotational parts
Part may require several operations and machines
High equipment cost
Significant tool wear
Large amount of scrap
Applications:
Machine components, shafts, engine components
Disclaimer: All process specifications
reflect the approximate range of a process's capabilities and should be
viewed only as a guide. Actual capabilities are dependent upon the
manufacturer, equipment, material, and part requirements.
Process Cycle
The time required to produce a
given quantity of parts includes the initial setup time
and the cycle time
for each part. The setup time is composed of the time to
setup the turning machine, plan the tool movements
(whether performed manually or by machine), and install
the fixture
device into the turning machine. The cycle time can be
divided into the following four times:
Load/Unload time
-
The time required to load the workpiece into the turning
machine and secure it to the fixture, as well as the
time to unload the finished part. The load time can
depend on the size, weight, and complexity of the
workpiece, as well as the type of fixture.
Cut time
-
The time required for the cutting tool to make all the
necessary cuts in the workpiece for each
operation. The cut time
for any given operation is calculated by
dividing the total cut length
for that operation by the feed rate,
which is the speed of the tool relative to the
workpiece.
Idle time
-
Also referred to as non-productive time, this is
the time required for any tasks that occur
during the process cycle that do not engage the
workpiece and therefore remove material. This
idle time
includes the tool approaching and
retracting from the workpiece, tool movements
between features, adjusting machine settings,
and changing tools.
Tool replacement time
-
The time required to replace a tool that has
exceeded its lifetime and therefore become to
worn to cut effectively. This time is typically
not performed in every cycle, but rather only
after the lifetime of the tool has been reached.
In determining the cycle time, the tool
replacement time is adjusted for the production
of a single part by multiplying by the frequency
of a tool replacement, which is the cut time
divided by the tool lifetime.
Following the turning process
cycle, there is no post processing that is required.
However, secondary processes may be used to improve the
surface finish of the part if it is required. The scrap
material, in the form of small material chips cut from
the workpiece, is propelled away from the workpiece by
the motion of the cutting tool and the spraying of
lubricant. Therefore, no process cycle step is required
to remove the scrap material, which can be collected and
discarded after the production.
Cutting parameters
In turning, the speed and motion of the cutting tool is
specified through several parameters. These parameters
are selected for each operation based upon the workpiece
material, tool material, tool size, and more.
Cutting feed - The distance that the cutting
tool or workpiece advances during one revolution of
the spindle, measured in inches per
revolution (IPR). In some operations the tool feeds
into the workpiece and in others the workpiece feeds
into the tool. For a multi-point tool, the cutting
feed is also equal to the feed per tooth, measured
in inches per tooth (IPT), multiplied by the number
of teeth on the cutting tool.
Cutting speed - The speed of the workpiece
surface relative to the edge of the cutting tool
during a cut, measured in surface feet per minute (SFM).
Spindle speed - The rotational speed of the spindle
and the workpiece in revolutions per minute (RPM). The spindle
speed is equal to the cutting speed divided by the circumference of the
workpiece where the cut is being made. In order to
maintain a constant cutting speed, the spindle speed
must vary based on the diameter of the cut. If the
spindle speed is held constant, then the cutting
speed will vary.
Feed rate - The speed of the cutting
tool's movement relative to the workpiece as the
tool makes a cut. The feed rate is measured in
inches per minute (IPM) and is the product of the
cutting feed (IPR) and the spindle speed (RPM).
Axial depth of cut - The depth of the
tool along the axis of the workpiece as it makes a
cut, as in a facing
operation. A large axial depth of cut will require a low
feed rate, or else it will result in a high load on
the tool and reduce the tool life. Therefore, a
feature is typically machined in several passes as
the tool moves to the specified axial depth of cut
for each pass.
Radial depth of cut - The depth of the
tool along the radius of the workpiece as it makes a
cut, as in a turning
or boring
operation. A large radial depth of cut will require
a low feed rate, or else it will result in a high
load on the tool and reduce the tool life.
Therefore, a feature is often machined in several
steps as the tool moves over at the radial
depth of cut.
Operations
During the process cycle, a variety
of operations may be performed to the workpiece to yield
the desired part shape. These operations may be
classified as external or internal. External operations
modify the outer diameter of the workpiece, while
internal operations modify the inner diameter. The
following operations are each defined by the type of
cutter used and the path of that cutter to remove
material from the workpiece.
External operations
Turning
- A single-point turning tool moves axially, along the
side of the workpiece, removing material to form different features,
including steps, tapers, chamfers, and contours. These features are
typically machined at a small radial depth of cut and multiple
passes are made until the end diameter is
reached.
Facing
- A single-point turning tool moves radially, along the end of the workpiece, removing a
thin layer of material to provide a smooth flat surface.
The depth of the face, typically very small,
may be machined in a single pass or may be
reached by machining at a smaller axial
depth of cut and making multiple passes.
Grooving
- A single-point turning tool moves radially,
into the side of the workpiece, cutting a
groove equal in width to the cutting tool.
Multiple cuts can be made to form grooves
larger than the tool width and special form
tools can be used to create grooves of
varying geometries.
Cut-off (parting)
- Similar to grooving, a single-point cut-off tool moves radially, into the side
of the workpiece, and continues until the center or
inner diameter of the workpiece is reached, thus parting
or cutting off a section of the workpiece.
Thread cutting
- A single-point threading tool, typically
with a 60 degree pointed nose, moves
axially, along the side of the workpiece,
cutting threads into the outer surface. The
threads can be cut to a specified length and
pitch and may require multiple passes to be
formed.
Internal operations
Drilling
- A drill enters the workpiece axially
through the end and cuts a hole with a
diameter equal to that of the tool.
Boring - A boring tool
enters the workpiece
axially and cuts along an internal surface to form
different features, such as steps, tapers,
chamfers, and contours. The boring tool is a
single-point cutting tool, which can be set to cut
the desired diameter by using an adjustable boring
head. Boring is commonly performed after drilling a hole in
order to enlarge the diameter or obtain more precise
dimensions.
Reaming - A reamer enters the
workpiece axially through the end and enlarges an existing hole to
the diameter of the tool. Reaming removes a minimal
amount of material and is often performed after
drilling to obtain both a more accurate diameter and
a smoother internal finish.
Tapping
- A tap enters the workpiece axially through
the end and cuts internal threads into an
existing hole. The existing hole is
typically drilled by the required tap drill
size that will accommodate the desired tap.
Equipment
Turning machines, typically
referred to as lathes, can be found in a variety of
sizes and designs. While most lathes are horizontal
turning machines, vertical machines are sometimes used,
typically for large diameter workpieces. Turning
machines can also be classified by the type of control
that is offered. A manual lathe requires the operator to
control the motion of the cutting tool during the
turning operation. Turning machines are also able to be
computer controlled, in which case they are referred to
as a computer numerical control (CNC) lathe. CNC lathes
rotate the workpiece and move the cutting tool based on
commands that are preprogrammed and offer very high
precision. In this variety of turning machines, the main
components that enable the workpiece to be rotated and
the cutting tool to be fed into the workpiece remain the
same. These components include the following:
Manual lathe
Bed
- The bed of the turning
machine is simply a large base that sits on the ground
or a table and supports the other components of the
machine.
Headstock assembly
- The headstock
assembly is the front section of the machine that
is attached to the bed. This assembly contains the
motor and drive system which powers the spindle.
The spindle supports and rotates the workpiece,
which is secured in a workpiece holder or
fixture,
such as a chuck or collet.
Tailstock assembly
- The tailstock
assembly is the rear section of the machine that is
attached to the bed. The purpose of this assembly is
to support the other end of the workpiece and allow
it to rotate, as it's driven by the spindle. For some
turning operations, the workpiece is not supported by
the tailstock so that material can be removed from the end.
Carriage
- The carriage is a platform that
slides alongside the workpiece, allowing the cutting tool
to cut away material as it moves. The carriage rests on
tracks that lay on the bed, called "ways", and
is advanced by a lead screw powered by a motor or hand wheel.
Cross slide
- The cross slide is attached
to the top of the carriage and allows the tool to move
towards or away from the workpiece, changing the depth of cut.
As with the carriage, the cross slide is powered by a motor
or hand wheel.
Compound
- The compound is attached on top of
the cross slide and supports the cutting tool. The cutting
tool is secured in a tool post which is fixed to the compound.
The compound can rotate to alter the angle of the cutting tool
relative to the workpiece.
Turret
- Some machines include a turret, which can
hold multiple cutting tools and rotates the required tool into
position to cut the workpiece. The turret also moves along the
workpiece, feeding the cutting tool into the material. While most
cutting tools are stationary in the turret, live tooling can also
be used. Live tooling refers to powered tools, such as mills,
drills, reamers, and taps, which rotate and cut the workpiece.
Tooling
The tooling that is required for
turning is typically a sharp single-point cutting tool
that is either a single piece of metal or a long
rectangular tool shank with a sharp insert attached to
the end. These inserts can vary in size and shape, but
are typically a square, triangle, or diamond shaped
piece. These cutting tools are inserted into the turret
or a tool holder and fed into the rotating
workpiece to
cut away material. These single point cutting tools are
available in a variety of shapes that allow for the
formation of different features. Some common types of
tools are as follows:
Style A - 0 degree lead-angle turning tools
Style B - 15 degree lead-angle turning tools
Style C - 0 degree square nose tools
Style D - 80 degree included angle pointed-nose tools
Style E - 60 degree included angle pointed-nose tools
Cutoff tools
Form tools
The above tools are often specified
as being right or left handed, which indicates in which
direction they move along the workpiece while making a
cut.
As described in the previous
section, live tooling can also be used for turning,
which includes the use of mills, drills, reamers, and
taps. These are cylindrical multi-point cutting tools
that have sharp teeth spaced around the exterior. The
spaces between the teeth are called flutes and allow the
material chips to move away from the workpiece. The
teeth may be straight along the side of the cutter, but
are more commonly arranged in a helix. The helix angle
reduces the load on the teeth by distributing the
forces. Also, the number of teeth on a cutter varies. A
larger number of teeth will provide a better surface
finish. The cutter teeth cover only a portion of the
tool, while the remaining length is a smooth surface,
called the shank. The shank is the section of the cutter
that is secured inside the tool holder.
All cutting tools that are used in
turning can be found in a variety of materials, which
will determine the tool's properties and the workpiece
materials for which it is best suited. These properties
include the tool's hardness, toughness, and resistance
to wear. The most common tool materials that are used
include the following:
High-speed steel (HSS)
Carbide
Carbon steel
Cobalt high speed steel
The material of the tool is chosen
based upon a number of factors, including the material
of the workpiece, cost, and tool life. Tool life is an
important characteristic that is considered when
selecting a tool, as it greatly affects the
manufacturing costs. A short tool life will not only
require additional tools to be purchased, but will also
require time to change the tool each time it becomes too
worn.
Materials
In turning, the raw form of the material is a piece of
stock from which
the workpieces are cut.
This stock is available in a variety of
shapes such as solid cylindrical bars and hollow tubes. Custom extrusions or
existing parts such as castings or forgings are also
sometimes used.
Round bar
Round tube
Custom extrusions
Turning can be performed on a
variety of materials, including most metals and
plastics. Common materials that are used in turning
include the following:
Aluminum
Brass
Magnesium
Nickel
Steel
Thermoset plastics
Titanium
Zinc
When selecting a material, several factors
must be considered, including the cost, strength,
resistance to wear, and machinability. The machinability
of a material is difficult to quantify, but can be said
to posses the following characteristics:
Results in a good surface finish
Promotes long tool life
Requires low force and power to turn
Provides easy collection of chips
Possible Defects
Most defects in turning are
inaccuracies in a feature's dimensions or surface
roughness. There are several possible causes for these
defects, including the following:
Incorrect cutting parameters
-
If the cutting parameters such as the feed rate, spindle speed,
or depth of cut are too high, the surface of the
workpiece will be rougher than desired and may contain
scratch marks or even burn marks. Also, a large depth of cut
may result in vibration of the tool and cause inaccuracies
in the cut.
Dull cutting tool
-
As a tool is used, the sharp edge will wear down and
become dull. A dull tool is less capable of making
precision cuts.
Unsecured workpiece
- If the
workpiece is not securely clamped in the fixture, the friction of
turning may cause it to shift and alter the desired cuts.
Design Rules
Workpiece
Select a material that minimizes
overall cost. An inexpensive workpiece may result in
longer cut times and more tool wear, increasing
the total cost
Minimize the amount of turning that is required
by pre-cutting the workpiece close to the
desired size and shape
Select the size of the workpiece such that a
large enough surface exists for the workpiece to be securely
clamped. Also, the clamped surface should allow clearance between the tool and the
fixture for any cuts
Features
Minimize the number of setups that are
required by designing all features to be accessible
from one setup
Design features, such as holes and
threads, to require tools of standard sizes
Minimize the number of tools that are
required
Ensure that the depth of any feature
is less than the tool length and therefore will
avoid the tool holder contacting the workpiece
Lower requirements for tolerance and
surface roughness, if possible, in order to reduce
costs
Avoid undercuts
Cost Drivers
Material cost
The material cost is determined by
the quantity of material stock that is required and the
unit price of that stock. The amount of stock is
determined by the workpiece size, stock size, method of
cutting the stock, and the production quantity. The unit
price of the material stock is affected by the material
and the workpiece shape. Also, any cost attributed to
cutting the workpieces from the stock also contributes
to the total material cost.
Production cost
The production cost is a result of
the total production time and the hourly rate.
The production time includes the setup time,
load time,
cut time, idle time,
and tool replacement time. Decreasing any of these time components will reduce cost. The setup
time and load time are dependent upon the skill of the
operator. The cut time, however, is dependent upon many
factors that affect the cut length and
feed rate. The
cut length can be shortened by optimizing the number of
operations that are required and reducing the feature
size if possible. The feed rate is affected by the
operation type, workpiece material, tool material, tool
size, and various cutting parameters such as the
radial depth of cut.
Lastly, the tool replacement time is a direct
result of the number of tool replacements which is
discussed regarding the tooling cost.
Tooling cost
The tooling cost for machining is
determined by the total number of cutting tools required
and the unit price for each tool. The quantity of tools
depends upon the number of unique tools required by the
various operations to be performed and the amount of
wear that each of those tools experience. If the tool
wear exceeds the lifetime of a tool, then a replacement
tool must be purchased. The lifetime of a tool is
dependant upon the tool material, cutting parameters
such as cutting speed,
and the total cut time. The unit price of a tool is affected
by the tool type, size, and material.
A lathe is a machine tool which turns cylindrical material, touches a cutting
tool to it, and cuts the material. The lathe is one of the machine tools
most well used by machining (Figure 1).
As shown in Figure 2, a material is firmly fixed to the chuck of a lathe.
The lathe is switched on and the chuck is rotated. And since the table
which fixed the byte can be moved in the vertical direction, and the right-and-left
direction by operating some handles shown in Fig. 3. It touches a byte's
tip into the material by the operation, and make a mechanical part.
Fig.1, Appearance of a Lathe
Fig.2, Chucking of Material
Fig.3, Handles of a Lathe
CAUTIONS!
When we use a lathe, the following things must take great care. (1) Don't keep a chuck handle attached by the chuck. Next, it flies at
the moment of turning a lathe. (2) Don't touch the byte table into the rotating chuck. Not only a byte
but the table or the lathe are damaged.
Three Important Elements
In orger to get an efficient propcess and beautiful surface at the lathe
machining, it is important to adjust a rotating speed, a cutting depth
and a sending speed. Please note that the important elements can not decide
easily, because these suitable values are quiet different by materials,
size and shapes of the part.
Rotating Speed
It expresses with the number of rotations (rpm) of the chuck of a lathe.
When the rotating speed is high, processing speed becomes quick, and a
processing surface is finely finished. However, since a little operation
mistakes may lead to the serious accident, it is better to set low rotating
speed at the first stage.
Cutting Depth
The cutting depth of the tool affects to the processing speed and the roughness
of surface. When the cutting depth is big, the processing speed becomes
quick, but the surface temperature becomes high, and it has rough surface.
Moreover, a life of byte also becomes short. If you do not know a suitable
cutting depth, it is better to set to small value.
Sending Speed (Feed) The sending speed of the tool also affects to the processing speed and
the roughness of surface. When the sending speed is high, the processing
speed becomes quick. When the sending speed is low, the surface is finished
beautiful. There are 'manual sending' which turns and operates a handle,
and 'automatic sending' which advances a byte automatically. A beginner
must use the manual sending. Because serious accidents may be caused, such
as touching the rotating chuck around the byte in automatic sending,.
Fig.4, Three Important Elements
A beginner of a lathe must operate with low rotating sopeed, small cutting
depth and low sending speed.
Cutting Tools for Lathe
There are vrious kinds of the cutting tools for a lathe. We must choose
them by the materials and shape of a part. Three typical cutting tools
are introduced in follows. Then we consider what is an easy process or
a hard process.
Form of Typical Cutting Tools
Figure 5(a) shows the most well-used cutting tool called a side tool. It
can process to cut an outside surface and an edge surface. Since the material
is set at the right of lathe, then this tool can only cut the right of
the material.
The cutting tool shown in Figure 5(b) is used at parting and grooving processes.
Its pointed end is slim, then it is too weak. Don't add a strong side-force
to the tool. This tool must send vertical direction only.
The cutting tool shown in Figure 5(c) is called a boring bar. It is used
to cut at an inside surface. It can make a big hole, which cannot be process
by a drill, and an high accurate hole.
Fig.5, Typical Cutting Tools
Easy Processing and Hard Processing
The general cutting tool, shown in Figure 5(a) is the most easy hangling.
Then the shape, which can be make using only the general cutting tool,
has easy processing.
In the case of the parting or prooving, The process becomes hard with decreasing
of the width of a alot, and increasing of the depth.
In the case of using of the boring bar, the process of a penetrated hole
is not so hard. But the process of no-penetrated hole is somewhat hard.
Because we cannot see the bottom surface in during process. In such cases,
we decide the location of the tool with the sound or the scale of lathe.
Moreover, the process of a small hole (less than 10 mm) or a depth hole
is too hard.
Of course, there are impossible shapes as shown in Figure 6(c). In such
case, the part must be divided or have any contrivances.
Fig.6, Easy Processing and Hard Processing
Hearing the Sound
In the case of the lathe process, sharpness is known from
scraps of the material or a processing surface. In addition, it is also
important to hear the sound. For example, when the sound is too high,
the processing is not suitable. It is caused by the bad edge of the
tool, too higher rotating speed of the lathe, or vibrating of a thin
material.
Setting of a Cutting Tool
In case a cutting tool is fixed to a table, thin metal plates are put between
the tool and the table, and the height of the edge is adjusted to the center
of material.
In the case of using the general cutting tool, when the edge is higher
than the center of material, the edge of a blade does not hit the material,
and it cannot cut at all. Conversely, if the edge is low, it becomes impossible
to cut the center of material. Moreover, the scale of a handle does not
have correct value, then accurate processing becomes impossible.
Fig.7, Height of Edge
If it says which it is ...
Though the height of the cutting tool is adjusted in
careful, we cannot unite with the center of material completely.
Therefore, we have to set the tool to the direction, that the edge is
easy to touch the material. The general cutting tool and the parting
tool have to be set a few low position. The boring bar has to set a few
high position.
Assortment of turning tools, including gouge, parting tool, larger gouge, and skew chisel, from left to right.
Let's Use a Lathe!
