Tack Hammer

Lathe Introduction

The metal lathe is designed to support and rotate a piece of material as it is being shaped by a cutting tool. The lathe can produce cylindrical, conical, helical and spherical shapes that are coaxial with the centre line of the lathe.

This type of lathe is often called a centre lathe. Small machines are usually mounted on a bench or a stand and sometimes called bench lathes. Bench lathes are available in various sizes, capable of turning lengths between about 600mm and 1000mm. Larger, heavy duty lathes can turn lengths up to 3 metres or more.

There are two main types of centre lathe. Lathes in which turning speeds are varied using step-cone pulleys are belt driven and are usually called belt-drive head lathes. Lathes that are driven through a gear box are usually called geared head lathes. The drive mechanism of a lathe is contained within the headstock as shown in the diagram below.

In the headstock, a spindle or main shaft is mounted in robust bearings that must are capable of withstanding heavy loads imposed by turning operations and maintaining the accuracy required for the finished job. The main functions of the headstock are to:

Support and rotate the workpieace.
House the speed changing mechanism.
Enable the work holding devices (Chucks) to be attached to the spindle.

The tailstock is made up of two castings. One rests on the guide ways and is clamped to the bed to suit the length of the work. The tailstock spindle or quill is housed in the upper casting which has a sideways adjustment. The tailstock spindle is bored to a standard morse taper to take centres, drill chucks and other attachments.

The carriage is the part of the lathe that supports and controls the movement of the cutting tool. It is comprised of the saddle which fits over and slides on the guide ways and the apron which is fastened to the saddle and hangs in front of the lathe bed. The apron carries the handwheel mechanism for the hand feed as well as the mechanisms for engaging the automatic feed and the lead screw.

Chucks

Lathe chucks are fitted to the spindle and are used to grip the work. Generally, two sets of jaws are provided with lathe chucks. One set for holding work externally, the other internally. Jaws for a self centering chuck must be fitted with identification amrks corresponding to those on the chuck. They must also be fitted in correct sequence.

The three jaw self centering chuck is made so that the three jaws all move together and are always the same distance from the centre. The three jaw chuck is gennerally used to hold round or hexagonal work.

Important safety tip: Once the chuck has been tightened to secure the work, ensure the chuck key must be removed from the chuck prior to starting turning on the lathe.

Cutting Speed & Machine RPM

Cutting speed is defined as the number of metres of material that passes the lathe tool in one minute, measured around the circumference of the work. Recommended cutting speeds depend on the type of material you are turning and the properties of the cutting tool. For example, Bronze has a faster cutting speed than steel because it is a much softer material. A tungsten carbide cutting tool will enable even higher cutting speeds on the same material compared to using high-speed steel cutting tools.

To achieve the required cutting speed the lathe has to be set to the correct RPM for the diameter of the material. This information can be read from a chart; however, it is useful to know how to calculate RPM when a chart is not available.

Example: Calculate the lathe RPM for rough turning a mild steel bar of 42mm diameter with a high-speed steel cutting tool.

The basic formula for calculating revolutions per minute is: RPM = Cutting Speed/Circumference.

When using a high-speed cutting tool, the cutting speed for rough turning mild steel is 30 metres per minute. Circumference of the bar is calculated as follows:

Circumference of the bar = ℼ x diameter of the bar

= (22/7) x 42mm

= 132mm

RPM = Cutting Speed/Circumference

= (30m x 1000) / 132mm (Note that the cutting speed 30m per minute is multiplied by 1000 to convert to mm)

= 230 approximately

Research - Subject Specific Terminology (SST)

Parallel Turning

Parallel turning or straight turning is a process used to cut the metal parallel to the axis. Parallel turning is done to decrease the diameter of the metal. When performing parallel turning, the cutting tool must always be set to the correct height (centre line of the work), just the same as when performing the facing process. Most turning is done from the tailstock toward the headstock using a right-hand tool. To go in the opposite direction, from the headstock toward the tailstock, use a left-hand tool.

It is good practice to set the tool during turning for safety in case cutting forces push the tool away from the workpiece. Keep the tool short for rigidity and be sure the tip is on centre. Then position the tool tip near the workpiece and move the carriage toward the headstock to the required location.

Important safety tip: Rotate the spindle by hand to check for clearance between the tool holder and compound rest and the chuck to make sure that there will be no collisions during machining. Repeat this process at the beginning point of the cut, especially if the workpiece is being supported by a tailstock mounted centre.

Watch this video to get a deeper understanding of parallel turning.

Centre Drilling

Work supported by a centre mounted in the tailstock must be drilled to fit the centre so a bearing surface is formed. Centre drilling is usually performed by mounting the workpiece in the lathe chuck and a centre drill in a drill chuck held in the tailstock.

The tailstock is positioned with the centre drill close to the workpiece. It is then locked to the guide ways and the centre drill is fed into the work using the tailstock hand wheel. The drill does not rotate but the work rotates as the drill is fed into it.

Important safety tip: The small pilots of centre drills are fragile, so apply adequate cutting fluid, use light feed and retract frequently to remove chips from the hole to prevent breakage.

Watch this video to get a deeper understanding of centre drilling.

Facing Off

Facing is the process of removing metal from the end of a workpiece to produce a flat surface. Most often, the workpiece is cylindrical, but using a 4-jaw chuck you can face rectangular or odd-shaped work to form cubes and other non-cylindrical shapes.

When a lathe cutting tool removes metal it applies considerable tangential (i.e. lateral or sideways) force to the workpiece. To safely perform a facing operation the end of the workpiece must be positioned close to the jaws of the chuck. The workpiece should not extend more than 2-3 times its diameter from the chuck jaws unless a steady rest is used to support the free end.

Choose a cutting tool with a slightly rounded tip. A tool with a sharp-pointed tip will cut little grooves across the face of the work and prevent you from getting a nice smooth surface. 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 workpiece at a slight angle. It is important that the tip of the cutting tool be right at the centre line of the lathe; if it is too high or too low you will be left with a little bump at the centre of the face.

Watch this video to get a deeper understanding of facing off.

Draw Filing

Draw filing is a technique used for producing smooth, square edges, particularly on pieces of metal. The process works by moving any type of single-cut file forwards and backwards along the length of the material's edge. By holding the file at 90° to the workpiece, the file’s teeth can cut on both the forward and the backward movement of the file.

Clamp the object you are going to be filing into a vice so that it is secure and doesn’t wobble around.
Grip each end of the file securely in the same way as you would grip the handlebars on a bicycle.
Standing at the side of the workpiece, slide the file forwards along the length of the area you want to smooth, applying light pressure.
Slide the file backwards along the length of the workpiece until you reach your starting position.
Repeat this technique until the area you are working on is filed to a smooth finish.

For more information on filing processes, click here.

Watch this video to get a deeper understanding of draw filing.

Thread Tapping

Taps are hardened tools used for cutting internal screw threads. There are three common types of taps; Taper Taps, Intermediate taps and Bottoming taps. Taps are held in tap wrenches so you can apply the rotational force necessary for the threading process.

The tapping hole is pre-dilled and should be smaller than the tap. The exact drill size required can be found from a tapping drill chart. However, for most metric threads the size can be calculated by the following formula: Tapping hole = D - p.
D is the outside diameter of the tap and p is the pitch.

Always use a suitable cutting oil when you are tapping and back off the cutting action when you feel resistance, every half turn, to break off the waste material. Taps are very hard and therefore very brittle. They will break if you apply too much pressure, particularly if you allow the waste material to build up.

Watch this video to get a deeper understanding of how to tap and cut threads.

Tolerances

Engineering tolerance is defined as a certain amount of allowable variation given to each dimension shown on an engineering drawing.

Why do tolerances exist?
They are an engineer's or designer's way of saying "so long as this print dimension is within this range, the machined part will function correctly." It is important to know the tolerances allowed, as this will determine what type of measuring tool will be needed to measure a dimension when machining.

A tolerance is applied to the print dimension to determine the largest and smallest acceptable size for the machined dimension. This is often called the upper and lower limit and the difference between the two is the total tolerance.

Lathe tool inserts are produced to dimensional tolerances. These tolerances ensure that the user can expect a certain amount of repeatability when the insert is continually used and replaced. Inserts made to tighter tolerances generally cost more to produce.

Watch this video to get a deeper understanding of measuring tolerances in industry.

2. Tool Identification

IND4-3 identifies and uses a range of hand and machine tools to produce quality practical projects

Lathe Tool

Lathe cutting tools are tools you can use with a lathe machine to produce turned parts and shape materials into the desired shape. There are three major classification categories for lathe cutting tools: material, uses, and method of applying feed.

Cutting edge material is commonly made from high speed steel, but sometimes carbide, tungsten or even diamond is used.

Your tool selection will be determined by the process you wish to complete such as, roughing, finishing, facing, boring, chamfering, knurling or thread cutting.

Thread Taps & Dies

Threading taps are a tool used to create screw threads (tapping) into a pre-drilled hole, to create a clean fitting for bolts in metals and plastics. Used in engineering and manufacturing, threading taps work like a drill but due to the unique shape of a tap, when screwed into a piece of material, screw threads are created. Threading taps must be used in a predrilled hole and cannot be used for drilling entire holes.

The difference between taps and dies is that taps are used to create or repair threads in holes which is ideal for nuts. Dies are used to cut threads on materials such as steel rods to allow a fitting to be screwed on and attached (threading). The tap is designed for internal thread cutting, so this would be used on the fastener hole or a nut, whereas a die is used for the external thread, like on a bolt. In other words, tapping uses the tap part of the set and creates internal threads and threading is the process used by the die to cut external threads.

Centre Drill

Centre drills are usually double sided drills with a 60' stepped point, held in a drill chuck or collet chuck in a lathe.

The purpose of the centre drill is to create an accurate centre hole in the face of a job so as a live centre can be inserted to support the weight and load of the job, whilst turning it.

Longer jobs generally require a live centre from the tailstock of the lathe to support the job, which prevents chatter and run out.

Centre drills can also be very useful in spotting or starting a precise hole, which will also give a chamfer on the hole; ideally used on the edge of round bar.

Click the button below to find out more about tool selection.

Lathe Tool Selection

4. Working Drawings

IND4-5 selects and uses communication techniques when designing, making and evaluating projects and ideas

Tack Hammer Handle

Tack Hammer Head

5. Steps of Construction

IND4-2 applies a design process in the modification of projects

Start by cutting a piece of 12mm square Bright Steel to a length of 70mm and a piece of 16mm diameter mild Steel to a length of 210mm (this allows a small amount of extra material which will be machined off during the turning processes).

Handle - Knurling

Set the metal Lathe, to the following settings:
- Speed 770rpm
- Feed direction is away from the headstock
- Feed rate = B,C,U,Z = 0.75mm
Using the same settings as the Centre punch. Knurl a length of 100mm. (see below)

a) Place the Mild Steel into a 3 Jaw Self-Centring Chuck on the metal Lathe, so that about 100mm protrudes out of the chuck.

b) Tighten the Chuck with the Chuck Key. Remove the Chuck Key from the chuck immediately.

c) Place a Knurling Tool into the Tool Post and tighten the 3 holding bolts down.

d) Position the Knurling Tool so that it will cut along the length of the Mild Steel (about 10mm away from the chuck)

e) Ensure that the Knurling Tool is tightened onto the Steel

Ensure that the coolant can flow easily and that it will flow over the Knurling Tool.
Use the Self feed mechanism to produce an even knurl along about 70mm of the Steel. DO NOT run off the end of your job.
Remove Knurling Tool and replace with a standard Lathe Tool in its holder, ensure that it is set to the correct centre height.

Handle - Facing the end

Without removing the Steel, engage the lathe tool so that it begins to cut and by rotating the Cross Slide Handle slowly move the tool out towards the inside of the job. Repeat until the end is flat.

Handle – End curve

Leave the job in this position. Using the Saddle Hand Wheel and the Cross Slide rough down the shape of the curve on the end of the handle.
Once the rough shape has been made move the tool bit and the Saddle out of the way and using a round file and emery cloth smooth and polish the curve.
Take your project out of the chuck and turn it around (protect the knurl using a sheet metal sleeve) retighten your project so that 140mm is protruding from the chuck.

Handle – Shaft and Neck

Using the Jacob’s chuck set in the Tail Stock centre drill the end of the steel.
Remove the Jacob’s chuck and replace with the Rotating Dead centre. Press the dead centre firmly in the centre drilled hole with the tail stock spindle wound out to 50mm. Ensure that the tail stock is lock down on the bed and the tail stock spindle is tightened and locked into place before machining.
Parallel turn the shaft to 12mm in diameter for a distance of 125mm. (allow for waste near the knurl to produce an internal curve of 3mm radius).
Place tool bit 22mm from the dead centre end of your shaft. Continue to parallel turn the shaft down to 9mm in diameter (again leaving waste in order to create a 3mm radius at the edge of the shoulder – see diagram)
Once 9mm has been reached roughly cut the radius to size. Using a round file and a smooth flat file smooth off the curves and the shaft. Polish the surfaces.
While the job is in the lathe, rotate the tool post and machine the end of the handle down to 8mm (this will be tapped to suit the screw thread on the hammer head. You can now remove the handle from the lathe.

Hammer Head

Using the 12mm square steel, mark out and file the slope on one end of the hammer head. (the 2mm shoulder made b cut using a hack saw).
Mark out, centre punch and drill a 6.5mm hole in the centre of the hammer head 30mm from the square end.
File the square end flat and file 2 x 6mm semi-circular curves in the head as shown in the diagram.

Tapping the threads

Using the M8 x 1.25 Tap and Die set cut the screw threads on the end of the handle and inside the hammer head.
The hammer head will require both the primary taper tap and the middling tap.
Ensure that cutting compound is used on both threads (Treflex).

Heat Treatment

The square end of the hammer head may be Hardened using the same process as the centre punch. The point of the job is heated to Cherry Red in colour by using the LPG (Liquid Petroleum Gas) Torch. It is then quenched into water to cool it.

Polishing

Re-clean the entire job with the Wet & Dry so that it is shiny.

Tack Hammer Handle Production

Tack Hammer Head Production

6. Project Evaluation

IND4-8 evaluates products in terms of functional use and aesthetics

To complete this section of you work report, refer to the project evaluation information on the carry tray page.

Tips for success:

Identify the key verb for each section of the evaluation.
Refer to the ALARM scaffold to understand how to respond to each section of the evaluation.
Write in full sentences by using the question to begin your response.
Check your spelling and grammar e.g. Have you used capital letters to begin sentences and full stops at the end?

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