Beginner's Guide to Operating an Automatic Screw Machine (Cam-Type Auto Lathe) | 3 Steps to Get Started

A Word Before We Start

Learning to operate an automatic screw machine (cam-type auto lathe / walking-tool lathe) requires one non-negotiable attitude: don't be afraid to get dirty. It is genuinely a dirty job. More importantly, you have to be proactive — no one will walk you through every step. Most of what you learn will come from your own hands-on experience and thinking.

That said, there is a clear learning path. Here are the 3 fundamental steps to becoming a competent automatic lathe operator.

Content authorized for publication by FULLERKREG.

Step 1: Understand Cutting Principles First

Before you ask how to design a cam, make sure you understand how the machine actually works. You cannot skip this step.

The core principle of a walking-tool (cam-type) automatic lathe is straightforward:

• The spindle rotates, holding and spinning the bar stock
• The cutting tools move — all cutting actions are achieved through tool movement, not spindle movement
• This is the origin of the name "walking-tool machine" (走刀机): the tools do the walking

All machining operations — turning, facing, chamfering, drilling, parting — are executed by coordinating the movement of multiple tool holders driven by cams.

Common Machine Size Designations

Automatic screw machines are typically designated by two numbers, for example: 1515, 2015, 1525, 2025.

Special machine configurations exist, but the above is the standard interpretation for most common models.

Step 2: Learn to Grind Cutting Tools and Drill Bits

This is the most important foundational skill — and the hardest to learn quickly. Setting up the machine is relatively straightforward once you understand it. Grinding tools correctly takes time and practice.

There is no shortcut here. The geometry of the cutting edge determines surface finish, tool life, chip formation, and dimensional accuracy. A poorly ground tool will cause problems that no amount of cam adjustment can fix.

Key points:

• Tool grinding is a skill developed through repetition — practice makes perfect
• Learn the correct rake angle, clearance angle, and nose geometry for the material being cut
• For stainless steel bar stock (e.g., SUS303), tool geometry is different from brass (C3604) or carbon steel (1215)
• Drill bit grinding for center drilling and through-hole operations is equally important

Step 3: Learn Machine Setup (Cam Adjustment)

Once you understand cutting principles and can grind tools, machine setup becomes learnable. The setup process also teaches you cam mechanics — which is the foundation for eventually designing your own cams.

Before You Touch the Machine: Read the Drawing

The first step of every setup is to study the part drawing and form a mental plan:

• How many tool passes are needed?
• Is the main diameter turned in one pass or two?
• Which tool holder does the chamfer? Which does the facing?
• What is the target cycle time (parts per minute)?

Have a clear plan before touching any cam or tool holder.

Typical Setup Sequence

The following is a common setup sequence. Note: experienced operators develop their own preferred order — this is one standard approach, not the only correct one.

1. Set Up the Parting (Cut-Off) Tool Cam

1. Rotate the cam lever to just before the collet-release position (slightly further back for larger diameter stock)
2. Adjust the parting tool cam to its highest point at this position
3. This completes the first cam
4. Run a test cut to part off the first piece
5. Tool holder ratios for positions 2, 3, 4: typically 1:1 to 1.5:1 (default 1:1)

2. Set the Stock Stop and Overall Length

1. Rotate the cam lever to just after the collet-clamp position
2. Adjust the stock stop bowl cam to just before its retract point
3. Adjust the plate cam to just before its lift point
4. Set the overall part length at this position

3. Set Up Tool #1 (Main Turning Tool)

1. Rotate the cam lever to when the stock stop arm lifts
2. Tool #1 ratio: 2:1 to 3:1 (2.5:1 is the most common default)
3. Mount the tool in the holder; bring the holder to the stock surface at the set overall length
4. If Tool #1 cuts on the down-stroke, position it at the intended infeed point
5. Adjust the bowl cam to its lowest point at this position
6. Continue rotating; at the highest point of the bowl cam, set the second plate cam to just before its lift point
7. Tool #1 cam setup is complete
8. Mount the tool, bring stock to the Tool #1 infeed position, lock the tool holder, and adjust the dimension

4. Set Up Remaining Tools

Once Tool #1 is set up correctly, the remaining tools follow the same logic with application-specific variations. If you can set up Tool #1, the others will follow.

Material Selection for Automatic Lathe Bar Stock

The material you run significantly affects setup difficulty, tool life, and cycle time. Free-machining grades are strongly preferred for automatic lathe production:

• Stainless steel: SUS303 (best machinability in stainless), SUS303Cu, SUS416F
• Carbon steel: 1215 (lead-free, RoHS), 12L14 (leaded, best machinability)
• Brass: C3604 (the easiest material to machine on automatic lathes)
• Aluminum: 6061-T651

For a full material selection guide, see: Common Bar Stock Materials for Automatic Lathes.

Summary: The Learning Path

Be patient, be proactive, and don’t be afraid to get your hands dirty.

Content authorized for publication by FULLERKREG.