Reference / Machine classes

Machine Classes Used for Large Parts

Once a part outgrows a machining centre it goes to one of nine places. Which one follows from the shape and the weight, not from the size alone.

Class	Typical envelope	Typical part weight
Travelling column mill	3 000 to 8 000 mm X, 1 000 to 1 500 mm Y, 800 to 1 500 mm Z	5 to 40 t, depending on bed construction
Horizontal boring mill, table type	2 000 to 5 000 mm X, 1 500 to 3 000 mm Y, spindle 110 to 160 mm	5 to 40 t on the rotary table
Horizontal boring mill, floor type	Column rails 5 000 to 30 000 mm, Y 3 000 to 6 000 mm, spindle 130 to 200 mm	Set by floor loading and crane, not by a table
Gantry or bridge mill	3 000 to 12 000 mm X, 2 000 to 4 000 mm Y, 1 000 to 2 000 mm Z	10 to 100 t on a fixed table
Vertical turning lathe	Swing 1 000 to 5 000 mm, height under rail 1 000 to 3 000 mm	5 to 100 t on the rotating table
Heavy horizontal lathe	Swing 600 to 1 600 mm, 3 000 to 12 000 mm between centres	2 to 40 t between centres, with steadies
Large vertical machining centre	1 500 to 3 000 mm X, 700 to 1 500 mm Y, 700 to 1 200 mm Z	2 to 10 t
Floor plate work	Set by the plate and the reach of the machine driven up to it	Set by floor loading, often 20 t per square metre or more
Portable and on-site machining	Bore 50 to 1 500 mm, flange facing to several metres	Not applicable, the equipment goes to the part

Travelling column mill

Also called Bed mill, moving column mill

Typical envelope: 3 000 to 8 000 mm X, 1 000 to 1 500 mm Y, 800 to 1 500 mm Z
Typical part weight: 5 to 40 t, depending on bed construction
What it is for: Long parts machined along their length, where the part stays put and the column travels.
Typical parts: Welded frames, beams, long base plates, press side members
Where it wins: Very long X travel without a very long table. The part is never moved once set.
Where it does not: Limited Y and Z. Awkward for tall parts and for bores deep into a vertical face.

Horizontal boring mill, table type

Also called HBM, table type borer

Typical envelope: 2 000 to 5 000 mm X, 1 500 to 3 000 mm Y, spindle 110 to 160 mm
Typical part weight: 5 to 40 t on the rotary table
What it is for: Housings and cases with bores on several faces that have to line up with each other.
Typical parts: Gearbox and mill housings, pump and valve bodies, bearing blocks, crusher frames
Where it wins: The rotary table indexes the part on a calibrated axis, so position between faces comes from the machine rather than from re-indicating.
Where it does not: Table rating caps the part weight. Long spindle extension costs rigidity.

Horizontal boring mill, floor type

Also called Floor borer, floor type HBM

Typical envelope: Column rails 5 000 to 30 000 mm, Y 3 000 to 6 000 mm, spindle 130 to 200 mm
Typical part weight: Set by floor loading and crane, not by a table
What it is for: Parts too heavy or too large for any rotary table, and work done on an assembled structure.
Typical parts: Press frames, machine beds, large fabrications, in-situ repairs
Where it wins: No table weight limit. Rails can run for tens of metres.
Where it does not: Every face needs the machine re-aligned to the part, so accuracy between faces depends on the alignment procedure and the operator.

Gantry or bridge mill

Also called Portal mill, bridge type machining centre

Typical envelope: 3 000 to 12 000 mm X, 2 000 to 4 000 mm Y, 1 000 to 2 000 mm Z
Typical part weight: 10 to 100 t on a fixed table
What it is for: Wide, flat parts where a large surface has to be flat and square to itself.
Typical parts: Press platens and bolsters, machine bases and cross rails, mould blocks, large plates
Where it wins: The part is clamped once and the bridge travels over it, so a whole face is cut inside one reference frame.
Where it does not: Weak on deep horizontal bores unless a right angle head is fitted, which costs rigidity and reach.

Vertical turning lathe

Also called VTL, vertical boring mill, VBM

Typical envelope: Swing 1 000 to 5 000 mm, height under rail 1 000 to 3 000 mm
Typical part weight: 5 to 100 t on the rotating table
What it is for: Round parts where the diameter is greater than the length.
Typical parts: Rings, flanges, tube sheets, slew bearing races, winch drums, turbine and pump casings
Where it wins: Part weight goes straight down into the table, so there is no off-axis load on the spindle. Many machines carry a live milling head, which removes a handling cycle.
Where it does not: No bar feeding. A practical height limit above the table. Long parts do not suit it.

Heavy horizontal lathe

Also called Roll lathe, oil country lathe

Typical envelope: Swing 600 to 1 600 mm, 3 000 to 12 000 mm between centres
Typical part weight: 2 to 40 t between centres, with steadies
What it is for: Round parts where the length is greater than the diameter.
Typical parts: Shafts, rolls, spindles, hydraulic cylinder bodies, long tubes
Where it wins: Tailstock and steady rest support along the length. Takes bar and long stock.
Where it does not: Heavy discs hang off the spindle and load it sideways, which is what a vertical lathe avoids.

Large vertical machining centre

Also called Large VMC, big bed machining centre

Typical envelope: 1 500 to 3 000 mm X, 700 to 1 500 mm Y, 700 to 1 200 mm Z
Typical part weight: 2 to 10 t
What it is for: The boundary class. Parts that have outgrown a standard machining centre but do not need a heavy machine.
Typical parts: Medium frames, plates, tooling, sub-assemblies
Where it wins: Fast, well tooled, and far cheaper per hour than a heavy machine.
Where it does not: Runs out of Z height and table load quickly. Not built for four metre spans.

Floor plate work

Also called Floor plate setup, plated work

Typical envelope: Set by the plate and the reach of the machine driven up to it
Typical part weight: Set by floor loading, often 20 t per square metre or more
What it is for: Parts that cannot go on any table, and assemblies machined in their final built state.
Typical parts: Very large fabrications, assembled frames, structures machined after welding
Where it wins: Removes the table as a constraint entirely.
Where it does not: Alignment is a procedure rather than a machine axis. Slower and more skill dependent.

Portable and on-site machining

Also called Field machining, in-situ machining

Typical envelope: Bore 50 to 1 500 mm, flange facing to several metres
Typical part weight: Not applicable, the equipment goes to the part
What it is for: Repairs and local features on installed equipment that cannot be moved.
Typical parts: Worn pin bores, stern tubes, flange faces, crusher and excavator structures
Where it wins: The tool is aligned to the part rather than to a machine table, which suits repair geometry. Avoids dismantling and downtime.
Where it does not: Low power and rigidity, so heavy stock removal is slow. Relating a feature to distant geometry needs survey equipment.

Every figure above is a typical range across machines from several builders and several decades. It is here so you can describe your part accurately in an RFQ, not as a capacity anyone holds. The shop that quotes you confirms what its own machine takes.

Reading further

Boring mill or gantryThe two most common routes for a heavy part, and how the shape decides it. Read the comparison
Floor or table typeWhat changes when the part is too heavy for any rotary table. Read the comparison
Vertical or horizontal latheDiameter greater than length points one way, length greater than diameter the other. Read the comparison
When the part outgrows a VMCThe four limits that decide whether a machining centre can still take it. Read the guide
Which machine your part wantsMachine bases, shafts, flanges, vessels and press tooling each point at a different class. Find your part type

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