VTL Machining Operations
On a VTL the table rotates in C and the tool moves in X and Z. That geometry supports the same turning operations as a horizontal lathe, but the setup and physics are different. Here's what you actually do on a VTL.
Facing
The tool moves radially inward (X direction) while the table spins. This produces a flat face. Because the work sits on a horizontal table, facing on a VTL is usually very flat and stable — the tool is rigidly mounted and the part doesn't sag.
Good practice: Face from OD toward ID (or vice versa consistently). Take a light skim cut at the end to clean up the face. The facing surface becomes your datm for height — watch for table flatness and clamping distortion.
OD Turning
The tool moves vertically (Z) along the outside diameter. Used for stepping diameters, turning tapers, and profiling the outer surface. Because the part is on a vertical table, gravity holds it down — heavy cuts are stable.
ID Turning / Boring
The tool reaches over the table and bores into the inside diameter. On a VTL this is often the most valuable operation: large rings, flanges, and valve bodies need accurate bores, and the VTL does it in the same setup as facing and OD turning.
Grooving, Parting, Profiling
- Grooving: Face grooves, OD/ID grooves for seals or retaining rings.
- Profiling: CNC-controlled X+Z interpolation for contoured shapes (turbine discs, valve seats).
- Taper turning: Simultaneous X+Z motion to cut angled surfaces.
Drilling & Boring on the VTL
With C-axis and a driven tool or a drill held in the ram, you can:
- Drill axially (downward) into the part centerline
- Bolt circle drilling — index C, drill each hole
- Tapping with rigid tapping
Example: Flange bolt circle
A 1200 mm flange has 12 holes on a 1000 mm bolt circle. On a VTL with C-axis, you program: face → turn OD → bore ID → index C to each hole position → drill. The part never leaves the machine. That's the VTL advantage — one setup does turning, boring, and hole patterns.
Typical VTL Workflow
| Step | Operation |
|---|---|
| 1 | Crane lowers forging/casting onto the table; clamp on pads or soft jaws |
| 2 | Probe to find part center and height; set G54 |
| 3 | Rough face and rough OD/ID (heavy stock removal) |
| 4 | Semifinish, then finish cut for print dimensions |
| 5 | Grooves, tapers, chamfers |
| 6 | C-axis operations: bolt circle drill, tap, or mill features |
| 7 | Probe check critical dimensions in-cycle |
| 8 | Unload; part goes to inspection |
What Makes VTL Operations Different
- Clamping strategy matters more: The part is bolted down, not gripped in a chuck. You need dedicated soft jaw pads or custom fixturing.
- Part must be balanced: An unbalanced 1000 kg disc spinning at 300 RPM will walk off the table and shake the building. Rough balance before first cut.
- Chip evacuation is vertical: Chips fall onto the table and around the part. Clean between operations — chips under the part cause wavy surfaces.
- Coolant floods: Big cuts need high coolant volume to clear chips and control heat.
Never leave a clamped part unattended during first cut. Especially on castings and forgings — the first cut may reveal a cracked or shifted forging. Start at low RPM and light feed, watch for chatter or pulling.