S

Sacrificial core

A temporary core removed after processing to leave an internal passage or cavity.

Sand casting

A casting process in which molten metal is poured into a cavity formed in sand.

Sanding

Abrasive finishing used to smooth surfaces, remove marks or prepare parts for coating.

Sanding sealer

A coating applied before sanding to fill pores and improve subsequent finish quality.

Satin finish

A smooth low-sheen finish between matte and gloss.

Sawing

A machining or stock-preparation process that cuts material with a toothed blade, including band, hacksaw and circular-saw operations.

Scan strategy

The programmed pattern in which an additive machine or laser scans each layer.

Scan-to-CAD

Reverse-engineering workflow in which scanned data are converted into usable CAD geometry.

Screw boss

A boss designed specifically to accept a screw, thread-forming screw or insert.

Screw recovery

The stage in which the screw rotates and retracts after injection to prepare the next shot. Also called dosing or metering, depending on machine and region.

Secondary machining

Machining carried out after the primary process such as moulding, printing or casting.

Selective laser melting

SLM; a metal powder-bed process that fully melts powder with a laser.

Selective laser sintering

SLS; a polymer powder-bed process that sinters powder using a laser.

Self-tapping screw boss

A plastic boss sized to accept a thread-forming screw without a separate insert.

Semi-gloss finish

A finish with moderate reflectivity, often specified for coated enclosures.

Set-up

The complete preparation of the machine, tools, workholding, programme and offsets needed to run a job.

Set-up sheet

A document listing the tools, offsets, fixtures and process details required for an operation.

SFM

Surface feet per minute; an imperial cutting-speed unit expressing the linear speed at the tool-work interface.

Shadowing

A finishing or scanning issue in which some areas are partially blocked from exposure, coating or inspection.

Sheet cutting

The profiling of flat sheet stock by processes such as laser cutting or waterjet cutting.

Sheet lamination

An additive category in which sheet material is bonded and cut layer by layer.

Sheet metal fabrication

The broader commercial discipline covering sheet cutting, bending, joining, deburring and finishing of sheet components.

Sheet metal forming

The shaping of sheet metal into required geometry by bending, stretching, stamping or related forming operations.

Sheet metal prototyping

Making prototype parts from sheet using cutting, bending, welding and fastening processes.

Shell moulding

A casting process in which a thin resin-bonded sand shell is formed around a heated pattern and then used as the mould cavity.

Shell thickness

The outer wall thickness of a printed or hollow structure.

Shore A

A hardness scale used mainly for softer elastomers.

Shore D

A hardness scale used for harder rubbers and many rigid plastics.

Short shot

An incompletely filled moulded part.

Shot blasting

A blasting process, often with metallic media, used for cleaning or peening metals.

Shot peening

A controlled blasting process that introduces compressive surface stress to improve fatigue life.

Shot size

The total volume or weight of melt injected in one cycle, including the part and runner where applicable. Correct shot-size selection is important for process stability and machine sizing.

Shrink line

A visible mark associated with local shrinkage differences in a moulded part.

Shrink-fit holder

A toolholder that grips a cutter by thermal expansion and contraction, offering high concentricity and rigidity.

Shrinkage

The dimensional reduction of a moulded part as the polymer cools from melt to solid. Shrinkage depends on resin type, wall thickness, gate location, packing and tool temperature.

Shrinkage allowance

Extra size built into tooling or patterns to compensate for expected material shrinkage.

Side-action

Another common term for a mould cam or slide used to form undercuts.

Silicone mould

A flexible mould, usually made from RTV silicone, used for vacuum casting and short-run reproduction.

Silk-screen printing

A printing method that transfers ink through a prepared mesh stencil.

Silver plating

The application of a thin silver coating for conductivity, reflectivity, solderability or appearance.

Sink mark

A local surface depression caused by non-uniform shrinkage, often above ribs or bosses.

Sinker EDM

A form of EDM that uses a shaped electrode to burn detailed cavities into a workpiece.

SLA

Stereolithography; a vat-photopolymer process that cures liquid resin with UV energy.

Slide

A moving mould component that forms a lateral feature and withdraws before ejection.

Slip fit

A fit with small clearance intended for easy assembly with limited play.

SLM

Abbreviation for selective laser melting.

SLS

Abbreviation for selective laser sintering.

Soft jaw

A machinable replaceable jaw fitted to a chuck and cut to suit the part.

Soft jaws

Machinable chuck jaws that are bored or milled to match a specific workpiece shape for repeatable turning set-ups.

Soft tooling

Tooling made for shorter life, lower volume or faster delivery than hard production tools.

Soluble core

A core designed to dissolve or wash out after moulding to leave complex internal geometry.

Solvent bonding

Joining plastics using a solvent that softens the surfaces and creates a fused bond.

Solvent smoothing

A broad term for using solvent action to reduce surface roughness on thermoplastic parts.

Spark erosion

A common workshop term for EDM.

Specimen coupon

A standardised test piece printed or machined alongside production parts for validation.

Speeds and feeds

The combined choice of spindle speed and feed parameters used to balance tool life, finish, cycle time and stability.

SPI

Society of the Plastics Industry mould-finish standard; a widely used system for specifying polished, semi-gloss and matte mould surfaces.

SPI A-1

The highest-polish SPI finish grade, produced with a very fine diamond buff for optically clear or mirror-like moulded surfaces.

SPI A-2

A high-polish SPI finish produced with a fine diamond buff for glossy moulded parts and transparent components.

SPI A-3

A medium-to-high polish SPI finish produced with diamond buffing for polished but not fully optical surfaces.

SPI B-1

A medium polish SPI finish typically produced with 600-grit paper.

SPI B-2

A medium polish SPI finish typically produced with 400-grit paper.

SPI B-3

A medium-to-low polish SPI finish typically produced with 320-grit paper.

SPI C-1

A low-polish stone finish in the SPI system, commonly associated with a restrained matte appearance.

SPI C-2

A low-polish SPI stone finish, rougher than C-1 and used for more subdued moulded surfaces.

SPI C-3

A coarser low-polish SPI stone finish used where a matte moulded appearance is acceptable or preferred.

SPI D-1

An SPI texture produced by dry blasting with glass bead media, giving a satin-like matte finish.

SPI D-2

An SPI texture produced by dry blasting with oxide media for a duller and rougher matte surface.

SPI D-3

The coarsest common SPI matte texture, produced by dry blasting with coarse oxide media.

Spindle

The rotating machine element that holds and drives the cutting tool or, in turning, may drive the workholding system containing the part.

Spindle speed

The rotational speed of the spindle in machining, usually given in revolutions per minute.

Split line

The visible line where tool sections separate, broadly similar to a parting line.

Spot drilling

A preparatory drilling step used to create a shallow starting cone that helps the following drill begin accurately.

Spotting drill

A short, rigid drill used to start a hole accurately and reduce drill wander before full drilling.

Sprue

The main feed channel that carries material from the machine nozzle into the runner system.

Sprue bushing

The hardened insert in the mould that receives melt from the machine nozzle and forms the sprue. It helps centre the nozzle interface and withstand repeated machine contact.

Sprue puller

A mould feature used to retain and pull the sprue from the stationary side when the tool opens so the runner system stays with the ejector side for release.

Squeeze die casting

A casting method that combines die filling with high-pressure squeezing to produce dense, low-porosity metal parts.

SRIM

Structural reaction injection moulding; a RIM variant that adds reinforcing structures or fibres to create stiffer structural parts.

Stair stepping

The stepped appearance on sloped additive surfaces caused by discrete layer height.

Standard resin

A general-purpose photopolymer resin used for concept models, visual prototypes and quick form checks.

Static mixer

A fixed mixing element used to combine two-part resins, silicones or adhesives.

Stationary platen

The fixed platen on the clamping unit, normally carrying the cavity-side half of the mould and interfacing with the machine nozzle.

Steam smoothing

A vapour-smoothing method using heated solvent or vapour to refine a thermoplastic surface.

Steel rule die

A thin-blade die used for cutting sheet materials, foams, gaskets and packaging prototypes.

STEP

A widely used neutral CAD format for exchanging precise solid geometry between systems.

STEP file

A neutral 3D CAD exchange file, usually .step or .stp, commonly preferred for CNC quoting and CAM preparation because it preserves precise solid geometry.

STEP files

Plural form of STEP file; neutral exchange files used to share accurate 3D CAD models across different software systems.

Stereolithography

The full term for SLA.

STL

A common tessellated file format for additive manufacture that represents surfaces as triangles.

Stock allowance

The extra material intentionally left on a part for later finishing, semi-finishing or clean-up passes.

Stone finishing

Mass finishing using abrasive stones or media to deburr and smooth parts.

Strain gauge test

Measurement of local strain using bonded electrical resistance gauges.

Stress relief

Thermal treatment used to reduce residual stress without major geometry change.

Stress whitening

The pale appearance that can develop in some polymers when highly strained.

Striation

A line or streak pattern, often referring to additive layer marks or machining feed marks.

Stripper plate

An ejection plate that pushes the part off the core using a broad contact surface rather than individual ejector pins. It is useful for thin-walled, cosmetic or cylindrical parts.

Structural reaction injection moulding

SRIM; a reaction injection moulding variant that incorporates structural reinforcement to create stiffer load-bearing parts.

Sub-spindle

A secondary spindle on a turning centre used to receive the workpiece for back-end operations or complete machining in one cycle.

Subtractive manufacturing

Making parts by removing material from stock through machining, cutting, grinding or similar processes.

Support density

The amount of support material generated in an additive build.

Support structure

Temporary geometry added during additive manufacture to support overhangs or anchor parts.

Surface energy

A surface characteristic that affects wetting, bonding, printing and coating behaviour.

Surface finish

In injection moulding, the texture, gloss and visual quality reproduced on the part surface from the tool, process conditions and resin. It may be specified by SPI, VDI 3400, Mold-Tech or customer-defined standards.

Surface grinding

A grinding operation used to produce very flat surfaces and fine finish.

Surface plate

A precision flat reference plate used for layout and measurement.

Surface roughness

The fine-scale texture of a surface, commonly specified using parameters such as Ra.

Surface speed

The linear speed at the cutting edge relative to the workpiece surface, usually expressed in m/min or SFM.

Surface treatment

A broad term for any secondary chemical, thermal, mechanical or coating process applied to alter a part’s surface properties or appearance.

Swirl finish

A non-directional finish made by random orbital sanding, often used on sheet metal signs and cosmetic components.

Swiss-type lathe

A sliding-headstock CNC lathe well suited to long, small-diameter precision parts.

Swiss-type turning

Also called sliding-head turning; a precision turning method in which bar stock is supported close to the cut by a guide bush.