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Fixture Body & Modular Systems

The fixture body carries every locating, clamping and guiding element. Its stiffness, weight and layout decide fixture accuracy and service life. For short runs, universal-adjustable, group and modular systems cut design and build time.

1Fixture Body — Requirements

Rigid enough to resist cutting force without deflection or vibration.
Stable and dimensionally accurate; machined in one setup where possible.
Light enough to handle, but massive where damping is needed (cast iron).
Chips and coolant must escape — open sides, slots, drain holes.
Locating and mounting surfaces machined flat and square to each other.

Rule of thumb: body stiffness, not clamp force, most often limits fixture accuracy.

2Body Construction Types

Cast iron body

Excellent rigidity and vibration damping; machinable; best for complex one-piece bodies (HT200). Slower and costlier to make.

Welded steel body

Fast and cheap for one-offs; stiff but less damping than cast iron; must be stress-relieved and machined after welding.

Fabricated plate body

Built from ground plate and standard sections (base plate, risers, gussets). Quick to assemble; very common for inspection and light fixtures.

Aluminium body

Light and fast to machine; lower stiffness; good for inspection fixtures and low-force work (6061-T6).

Universal-Adjustable Fixtures

A universal-adjustable fixture covers a family of similar parts by adjusting locators and clamps, without a new fixture for every size. Typical: adjustable V-block centres, sliding jaw vises, adjustable drilling boxes.

Adjustment ranges cover several part sizes in one fixture.
Setup is quick, but accuracy must be re-checked after each adjustment.
Best for small-to-medium batches of dimensionally similar parts.

Group (Family) Fixtures

In group technology, parts are classified into families with the same locating and clamping scheme. One group fixture, with small interchangeable elements, serves the whole family.

Family classified by shape, size range and datum scheme.
Base fixture is permanent; only small elements change per part.
Reduces the number of fixtures and changeover time.

Effective where 30–70% of a shop's parts can be grouped into families.

Modular Fixture Systems (组合夹具)

Modular systems assemble a fixture from a standard kit of precision elements — base plates, locators, supports, clamps, links and fasteners. The fixture is built, used and dismantled, so the same elements serve many jobs.

T-slot based: elements bolt into a grid of T-slots; flexible and fast.
Dowel-pin based: elements locate on precision dowel grids; higher accuracy and rigidity.
No machining of the fixture itself — only assembly.
Excellent for prototypes, short runs and urgent jobs.

Assembly (Built-Up) Fixtures

A built-up fixture is assembled on the machine from standard elements and adjusted in place. It is the fastest way to a working fixture but the least rigid and accurate; fine for one-offs and verification.

Assembled directly on the machine table with clamps, parallels and angle plates.
Low cost and instantly available; limited rigidity and repeatability.
Upgrade to a dedicated or modular fixture once the design is proven.

A T-slot base plate with standard locators, supports and clamp builds a working fixture quickly.

A precision dowel grid gives the accuracy and rigidity of a dedicated fixture.

A built-up fixture: angle plate and parallels stacked and clamped straight on the machine table.

A group fixture: one permanent base with a fixed datum and an adjustable stop serves an entire family.

Choosing the Approach

Situation	Recommended
One-off prototype or repair	Built-up / assembly fixture
Short runs, frequent changeover	Modular system (T-slot or dowel-pin)
Family of similar parts, medium batch	Universal-adjustable / group fixture
Large batch, high accuracy	Dedicated cast or welded fixture