Horizontal Machining Centers (HMC)

A horizontal machining center has its spindle lying on its side, pointing at a part that stands upright on a pallet. The pallet sits on a rotary table, the B axis, so the machine reaches four sides of a part, or four faces of a tombstone fixture loaded with parts, without anyone opening the door. Chips fall away from the cut instead of collecting on the work. A pallet changer swaps the finished pallet for a loaded one, and the operator sets up the next job while the machine cuts.

That combination makes the horizontal a production machine. It takes more floor space and more fixturing than a vertical machining center, which is worth it when the same parts run in volume or when a pallet pool keeps the spindle cutting through the night. Floor-type and table-type machines for single heavy workpieces are listed under CNC boring machines. Parts that need tilted features in one clamping point to 5-axis machining centers.

Pallet size and pallet load define the class, so compare those first, along with the largest workpiece diameter and height that can swing on the table. Then the travels, the spindle taper, speed and torque, and the tool magazine, which is often large because one pallet may carry several different parts. Ask how many pallets the machine can be extended to.