How spare parts are manufactured

How do you cut a drive sprocket? We glean ideas from a machine show

Driven cogs, cams and gears don't form themselves out of thin air.
Driven cogs, cams and gears don't form themselves out of thin air.
Driven cogs, cams and gears don't form themselves out of thin air.
Driven cogs, cams and gears don't form themselves out of thin air.
Modern tools such as this rotary table ensure faster and better production of those essential spare parts.
Modern tools such as this rotary table ensure faster and better production of those essential spare parts.
Manufacturing tracks is a precision affair.
Manufacturing tracks is a precision affair.
Every millimetre counts if parts are to be strong and reliable
Every millimetre counts if parts are to be strong and reliable
Modern lathes are almost clinical, to ensure nano-metre perfect finishes.
Modern lathes are almost clinical, to ensure nano-metre perfect finishes.
Most modern CNC-controlled machines are completely enclosed for safety reasons.
Most modern CNC-controlled machines are completely enclosed for safety reasons.


So, how do you cut a drive sprocket? A machine tool show gives us some idea how spare parts are manufactured

Consider an excavator, or a bulldozer, or any other piece of construction equipment for that matter. They are each made of tens of thousands of parts, but have you ever wondered those beautifully machined parts come from in the first place?

Of course, most of the structure is either pressed or cast, and most of us have a concept of how this might be done, but what about components that are hewn from a block of solid metal? You might be familiar with the lathe, but how on earth do you cut, say, a gear for a differential?

We were so fascinated by this subject, we hopped on the next available plane to Taiwan, where the world’s largest exhibition of machine tools was being held. At the event, around 900 exhibitors showed off their wares. Don’t forget, this event was just for machine tools, not actual machines, so clearly manufacturing is still very big business in the Far East, even with the downturn hitting Taiwan like a ‘financial tsunami’ in the words of the island’s prime minister.

Machining Centres

One of the first principals of shaping metal is that it is all about removing excess material, as precisely and efficiently as possible. It might sound obvious, but very few machines ever try to form a work piece by adding material – with the possible exception of rapid prototyping which involves material being formed by a chemical process.


The three principal machining processes are classified turning drilling and milling. Other operations falling into miscellaneous categories include shaping, planing, boring, broaching and sawing Turning operations are operations that rotate the workpiece as the primary method of moving metal against the cutting tool. Lathes are the principal machine tool used in turning where the tool stays still and the workpiece turns, while in milling, the tool turns while the workpiece stays still.

Obviously, you will know what a drill does, but in engineering terms a ‘drilling operation’ is where holes are produced or refined by bringing a rotating cutter with cutting edges at the lower extremity into contact with the workpiece.

Drilling operations are done primarily in presses but not uncommonly on lathes or mills.

There are other miscellaneous operations that can be done with machine tools, such as burnishing,  which is the generally undisarable effect of two surfaces rubbing against each other. However, there are a few instances where burnishing can be used in the manufacturing process. 

An unfinished workpiece requiring machining will need to have some material cut away to create a finished product. A finished product would be a workpiece that meets the specifications set out for that workpiece by blueprints.

For example, a workpiece may be required to have a specific outside diameter. A lathe is a machine tool that can be used to create that diameter by rotating a metal workpiece, so that a cutting tool can cut metal away, creating a smooth, round surface matching the required diameter and surface finish.

A drill can be used to remove metal in the shape of a cylindrical hole. Other tools that may be used for various types of metal removal are milling machines, saws, and grinding tools. More recent, advanced machining techniques include the electrical discharge machine (EDM), electro-chemical erosion, water jet, or laser cutting to shape metal workpieces.

 Although a machine shop can be a stand alone operation, many firms who run and maintain their own heavy equipment maintain their own internal machine shops .

Machining requires attention to many details for a workpiece to meet the specifications set out in the engineering drawings or blueprints. Beside the obvious problems related to correct dimensions, there is the problem of achieving the correct finish or surface smoothness on the workpiece.

The inferior finish found on the machined surface of a workpiece may be caused by incorrect clamping, dull tool, or inappropriate presentation of a tool. Frequently, this poor surface finish, known as chatter, is evident by an undulating or irregular finish, and the appearance of waves on the machined surfaces of the workpiece.

CNC Control

CNC, or computer numerical control, is vital for just about any tool used in component manufacturing in modern times. Systems vary, but the computer will always pinpoint the machining heads to an exact position in the work area. This means it is easy to set up a program to completer repetitive tasks. Older systems were limited to working on onlyleft and right or forward and back axis, but modern equipment can handle 3D tasks, with many machines managing work on five, or even six axis.

Machines that required automation to repeat tasks were engineered back in the 1890s, but the first numerical control machines appeared in the 1950s.Being able to automatically move a tool to a predefined point many times was a milestone in engineering terms, and the foundation of modern robotics.


CNC lathes have all but replaced the older production latheres from the toolroom due to their ease of setting and operation. They are designed to use modern carbide tooling. When the part that the machine is going to produced is designed, the ‘toolpaths’ are programmed by computer.

The machine is controlled electronically by the computer, which typically has a screen telling the operator the position of the tool, the progress of the work piece as well as much else besides. Of course, you would need to be a specialist to operate such a machine, but the level of operator input needed when the programme is running is much less, meaning a bank of such machines could be controlled by one technician.

A CNC lathe is much cheaper now than it would have been a few years ago, however it would still be very expensive to have one in the workshop for occasional use. That said, there are now companies who can supply machines for small workshops and hobbyists, thanks to open-source software and the lower production costs of the Far East.


Most milling machines (also called machining centres) are computer controlled vertical mills with the ability to move the spindle vertically along the Z-axis. When used with conical tools, it also significantly improves milling precision without impacting speed.

The most advanced CNC milling-machines, the 5-axis machines, add two more axes in addition to the three normal axes (XYZ). Horizontal milling machines also have a C or Q axis, allowing the horizontally mounted workpiece to be rotated, essentially allowing asymmetric and eccentric turning.

Meanwhile, the fifth axis (B axis) controls the tilt of the tool itself. When all of these axes are used in conjunction with each other, extremely complicated geometries, even really difficult shapes like a gearbox pressure-case be made with relative ease with these machines.

But the skill to program such shapes is beyond that of most operators. So, 5-axis milling machines are practically always programmed with computer-aided modeling, or CAM.

Like lathes, the once huge price of machining centres is coming down. Will one find a home in your workshop?

Machine tool makers hopeful about Middle East market

Asian machine tool manufacturers remain optimistic about trade with the Middle East, despite the global economic meltdown.

But, concerns over machines being purchased in bulk and re-exported by unauthorised middle men, as well as general concerns regarding the recession, have deterred several large firms from pursuing business leads in the region. In Persia, trade sanctions with Iran have been cited as another reason.

Jade Chen, general manager of Chin Fong Machine said: “The Middle East is a rising market that we want to focus on.”

“Last year we signed a deal with a firm in Dubai – a joint venture. We also have a deal to supply equipment in Turkey.”

He added: “For cost reasons, [the customers] often first check Chinese suppliers, but for quality and performance factors, more and more, they are coming to Taiwan.”

This view was echoed by others, though with a note of caution. “The market demand is small, but increasing in the Middle East,” said Michael Shih, president of Falcon Machine Tools. “However, we have to be careful. From my understanding, some machines shipped to [the region] have then been re-exported to other countries.”

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