What is the difference between an HMC and a VMC?

An HMC's spindle is horizontal and it usually has a rotary table and pallet changer, so it machines several faces in one setup and is more productive for batches. A VMC is vertical, cheaper and quicker to set up for plates and small batches.

What is a tombstone on an HMC?

A tall fixture block on the pallet with parts clamped on its faces, so many parts are machined in one cycle.

When is HMC job work worth it?

For box-shaped parts with features on several faces, made in batches: housings, valve bodies, pump casings and gearbox cases.

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HMC (horizontal machining centre)

Also called: horizontal machining center, HMC machine, horizontal milling machine, HMC job work

An HMC (horizontal machining centre) is a CNC machining centre with a horizontal spindle and, usually, a rotary table and two pallets. It machines several faces of a box-shaped part in one setup and loads the next part while cutting, which makes it very productive for batch work.

Quick facts

Spindle: Horizontal
Rotary table: Usually indexes or rotates the part (B axis) to reach four sides
Pallets: Commonly two, so one is loaded while the other is cut
Common pallet sizes: 400, 500, 630 and 800 mm square
Typical accuracy: Around ±0.01 mm, very good for hole positions across faces
Best for: Housings, valve bodies, pump casings, gearbox cases

How an HMC works

The part is fixed on a pallet, often on a tall fixture (a tombstone) that holds several parts. The table turns the part so the horizontal spindle can reach each face. Chips fall away from the cut, which helps in deep pockets.

While one pallet is inside being machined, the operator unloads and loads the other outside, so the spindle keeps cutting.

Advantages

Four sides (and more with a tilting table) in one setup, so features line up accurately
Pallet changer keeps the spindle busy: high output for batches
Chips fall away, giving better tool life and surface in deep pockets
Tombstone fixtures hold many parts per cycle

Limits

Costs more to buy and run than a VMC of similar size
Needs more planning: fixtures and programs for each part
Less suited to flat plates and one-off jobs, where a VMC is quicker to set up

HMC or VMC?

	HMC	VMC
Spindle	Horizontal	Vertical
Faces per setup	Several (rotary table)	One (3-axis)
Chip removal	Chips fall away	Chips can stay in pockets
Pallet changer	Usually yes	Usually no
Best for	Box parts in batches	Plates, moulds, small batches

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Related job work

VMC / CNC milling

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Questions

What is the difference between an HMC and a VMC?: An HMC's spindle is horizontal and it usually has a rotary table and pallet changer, so it machines several faces in one setup and is more productive for batches. A VMC is vertical, cheaper and quicker to set up for plates and small batches.
What is a tombstone on an HMC?: A tall fixture block on the pallet with parts clamped on its faces, so many parts are machined in one cycle.
When is HMC job work worth it?: For box-shaped parts with features on several faces, made in batches: housings, valve bodies, pump casings and gearbox cases.

The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 8 October 2026.