Subtractive Manufacturing and Materials

The process has physical width

A cut is not infinitely thin.

A saw blade has thickness.

A router bit has diameter.

A milling cutter has diameter.

A laser cut has a kerf.

A plasma arc and waterjet also remove a measurable width of material.

The width of material removed during a cutting process is often described as the kerf.

Imagine a 100 mm square drawn in CAD.

If a cutting process simply travels directly along that line while removing material from both sides of it, the final part may not measure exactly 100 mm.

Manufacturing software or the operator may compensate by offsetting the cutting path.

This is why fabrication geometry cannot always be interpreted as abstract lines alone.

Roughing and finishing

Removing a large amount of material and producing a high-quality final surface are not always best achieved with the same operation.

A roughing pass prioritises efficient material removal.

It may deliberately leave a small amount of material behind.

A later finishing pass removes the remaining material under conditions chosen to improve dimensional accuracy or surface finish.

This principle appears in many forms of machining.

The final surface can therefore depend on both the geometry and the strategy used to produce it.

Timber

Timber is commonly sawn, drilled, routed, turned, sanded and machined.

It is anisotropic: its grain direction influences how it behaves.

Cutting with, across or against grain can affect surface quality and the tendency to split or tear.

Timber fabrication also creates dust, which may require extraction and appropriate respiratory controls.

Workholding needs to control the material without unnecessarily damaging the finished surface.

Aluminium

Aluminium is widely used because it is lightweight, corrosion resistant and comparatively easy to machine.

It can be sawn, drilled, milled, turned, routed and cut using several CNC processes when suitable tooling and machine parameters are used.

Aluminium components are also commonly anodised, painted or powder coated after fabrication.

Because these later processes can affect surfaces and dimensions, the final finish should be considered during the design stage.

Steel

Steel is stronger and generally more demanding to cut than materials such as timber or many aluminium alloys.

Depending on the job, it may be sawn, drilled, milled, turned, ground, laser cut, plasma cut or waterjet cut.

Different steel grades can behave differently during machining and welding.

Heat, cutting forces and tool wear can become major considerations.

Polymers

Plastics and other polymers can be machined, routed, sawn, drilled and sometimes laser processed.

But “plastic” is a broad material category.

Different polymers can melt, chip, soften, burn or release hazardous decomposition products under inappropriate processing conditions.

A process that is appropriate for one plastic should not automatically be assumed safe for another.

Material identification matters.

Composites

Composite materials combine different materials to produce useful properties.

Examples include fibre-reinforced polymers and laminated products.

Their mixed structure can make machining more complicated because different components respond differently to cutting.

Dust from some composite materials can also be hazardous.

Tooling, extraction and handling requirements therefore depend strongly on the particular composite being processed.

Stone

Stone is commonly shaped using abrasive and diamond tooling.

Sawing, grinding, drilling and waterjet cutting are common processes.

Stone processing can create significant dust, and some stone products can contain respirable crystalline silica, making dust control particularly important.

The material can also be brittle, meaning forces and workholding need to be considered carefully.

Glass

Glass requires a different way of thinking again.

Some glass can be scored and deliberately fractured along the score.

Other operations use grinding, drilling, abrasive processes or waterjet cutting.

Glass is brittle, so stresses that would merely bend a metal component may fracture a glass one.

Again, the geometry alone does not define the manufacturing process.

Material, tool and process belong together

There is no universal cutting method.

Selecting a manufacturing process requires consideration of:

material + geometry + machine + tooling + tolerance + finish + quantity

A process that is perfect for one combination may be completely unsuitable for another.