What Is an Automatic Screw Machine?
An automatic screw machine (automatic lathe) is a high-performance, high-precision, low-noise production machine tool designed for continuous, unattended machining of small precision parts. In its most common form, it uses cams to control the machining sequence — one complete cam revolution produces one finished part.
Automatic screw machines are particularly suited for machining copper, aluminum, steel, and plastic precision components. They are widely used in industries including instruments, watches, automotive, motorcycles, bicycles, eyewear, stationery, hardware and sanitary fittings, electronic components, connectors, computers, mobile phones, electromechanical equipment, and defense manufacturing — especially for batch production of small, complex parts.
The core characteristic of all automatic lathe types is the ability to run continuously and automatically after setup, producing the same part repeatedly without operator intervention.
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Two Fundamental Machine Types: Swiss-Type vs Walking-Tool
1. Swiss-Type (Walking-Spindle / 走心式)
In a Swiss-type automatic lathe:
- The collet clamps the bar stock
- The material moves forward (the spindle/stock walks)
- The cutting tools remain stationary in the radial direction, performing linear or rocking motion
- The guide bushing supports the stock very close to the cutting point, enabling extremely high precision on long, slender parts
Swiss-type machines excel at long, thin, high-precision parts where length-to-diameter ratio is high.
2. Walking-Tool Type (Cam Auto Lathe / 走刀式)
In a walking-tool automatic lathe:
- The collet clamps the workpiece (stock does not move axially during cutting)
- The cutting tools move — left, right, forward, and backward — to perform all machining operations
- All cutting actions are achieved through coordinated tool movement
- This is the origin of the name "walking-tool machine" (走刀机)
Walking-tool cam machines are the most common type for high-volume production of short, complex parts.
Walking-Tool Cam Automatic Lathe: Detailed Specifications
Tool Configuration
A standard walking-tool cam automatic lathe is equipped with 5 tool holders, numbered 1 through 5:
| Tool Position | Primary Function |
|---|---|
| Tool #1 | Turning outer diameter (OD) |
| Tool #2 | Grooving, chamfering, or secondary operations |
| Tool #3 | Grooving, chamfering, or secondary operations |
| Tool #4 | Grooving, chamfering, or secondary operations |
| Tool #5 | Turning outer diameter (OD) or parting |
Each tool holder can accommodate 1–2 cutting tools. Additionally, the machine is equipped with:
- 2 tail spindles
- 2 drill bits
- 1 tap and 1 die
All operations run simultaneously, enabling complex parts to be completed in a single pass including: OD turning, spherical surfaces, tapers, arcs, steps, grooving, knurling, drilling, tapping, die threading, and parting.
Machine Size Designations
Common models: 1515, 2015, 1525, 2025
| Designation | First Two Digits | Third Digit | Fourth Digit |
|---|---|---|---|
| 1515 | Max bar stock Ø 15 mm | 1 spindle | 5 tool holders |
| 2025 | Max bar stock Ø 20 mm | 2 spindles | 5 tool holders |
Precision Specifications
| Parameter | Specification |
|---|---|
| Spindle accuracy | 0.003 mm |
| Dimensional control accuracy | 0.005 mm (micrometer-controlled slide fine adjustment) |
| Spindle speed | 2,000–8,000 RPM |
| Minimum infeed increment | 0.005 mm |
| Surface roughness (brass parts) | Ra 0.04–0.08 μm |
Production Efficiency
- Cam speed: 1.0–36 RPM (adjustable per part)
- Typical output: up to ~30 parts per minute
- 5 tools cutting simultaneously — production efficiency far exceeds standard CNC lathes and instrument lathes
- One operator can supervise multiple machines simultaneously
Automatic Bar Feed
- Bar stock is automatically fed to the spindle by the feed mechanism
- Machine automatically stops and alarms when bar stock is exhausted
- No manual stock monitoring required during production — fully automated manufacturing process
Cam Mechanism: How It Works
Cam-type automatic lathes use two types of cams to control all tool movements:
Bowl Cam (Cylindrical Cam / 磗形凸轮)
- Cylindrical in shape; the end face is machined into the required profile
- As the cam rotates, the profile drives a connecting rod and rocker arm
- Converts rotary cam motion into linear tool holder motion in the axial direction (along the workpiece axis)
- Controls axial (Z-axis) cutting movements
Plate Cam (Disc Cam / 板形凸轮)
- Disc-shaped; the outer periphery is machined into the required profile
- As the cam rotates, the profile drives a connecting rod linked to the tool holder
- Converts rotary cam motion into linear tool holder motion in the radial direction (perpendicular to the workpiece axis)
- Controls radial (X-axis) cutting movements
By combining the axial motion of the bowl cam and the radial motion of the plate cam, the cutting tool can travel in diagonal or curved paths, enabling complex contour machining.
Jie-Type Automatic Lathe (捷式自动车床)
The Jie-type automatic lathe is a simplified variant of the standard walking-tool cam auto lathe. It eliminates the Tool #1 holder and the tapping unit, making it suitable for simpler parts that do not require tapping operations.
| Feature | Standard Cam Auto Lathe | Jie-Type Auto Lathe |
|---|---|---|
| Tool #1 (OD turning) | Yes | No |
| Tapping unit | Yes | No |
| Suitable for | Complex parts, tapped holes | Simple parts, no tapping required |
| Machine cost | Higher | Lower |
| Best for | Full-featured precision parts | High-volume simple turned parts at lower cost |
The Jie-type is a cost-effective solution for customers with long-term, high-volume production of simple turned components.
Other Automatic Lathe Types
- CNC Automatic Lathe: Uses CNC control instead of cams. More flexible for changeovers and complex geometries; lower output rate than cam machines for simple parts.
- Pneumatic Automatic Lathe: Uses pneumatic actuation for tool movements. Simpler mechanism, suitable for specific applications.
Related Guides
- Beginner’s Guide to Operating an Automatic Screw Machine
- Common Bar Stock Materials for Automatic Lathes
- SUS303 Free-Machining Stainless Steel
- C3604 Free-Cutting Brass
- 1215 Free-Cutting Steel
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