1204 vs 1605 Ball Screw for Small CNC Machines

Introduction

When building a small CNC router, desktop engraver, or DIY motion system, the debate between 1204 vs 1605 ball screws is one of the most common technical hurdles. While both are staples in the compact CNC world, they offer different mechanical advantages that can significantly impact your machine's performance, especially when cutting materials like wood or aluminum.

A 1204 ball screw features a 12mm diameter and a 4mm lead, whereas a 1605 ball screw has a 16mm diameter and a 5mm lead. Choosing the right one isn't just about size-it's about balancing rigidity, speed, and your motor's torque curve.

Technical Breakdown: 1204 vs 1605 ball screw

What Does 1204 Mean?

1204 ball screw diameter:12mm

1204 ball screw lead:4mm

Lead vs. Pitch: In single-start ball screws, these are the same. A 4mm lead means the nut moves 4mm for every full 360° revolution.
Mechanical Advantage: The 4mm lead acts like a "lower gear" compared to 5mm. It provides higher thrust force and finer resolution (0.01mm travel per step in half-step mode), making it excellent for precision tasks.

What Does 1605 Mean?

1605 ball screw diameter:16mm

1605 ball screw lead:5mm

The "Industry Standard": 1605 is the most widely used size for hobby CNCs. It offers a 16mm diameter which provides significantly higher rigidity than 12mm.
Speed Advantage: The 5mm lead allows for faster linear travel at lower motor RPMs, which is critical for maintaining "chip load" during high-speed spindle operations.

1204 vs 1605: Basic Specification Comparison

Specification	1204 Ball Screw	1605 Ball Screw
Nominal Diameter	12mm	16mm
Lead (Travel per Rev)	4mm	5mm
Mechanical Gear Ratio	Lower (Higher Torque)	Higher (Higher Speed)
Rigidity	Moderate (Good for Z-axis)	High (Standard for X/Y)
Space Requirement	Compact (Small Nut)	Larger (Requires Clearance)
Common Application	PCB Mills, Light Engravers	Small Routers, Heavy Spindles

Key Considerations from the CNC Community

Based on real-world feedback from CNC builders (such as those on r/hobbycnc), here are the critical factors that often get overlooked in technical data sheets:

1. Rigidity and Critical Speed

Rigidity is the most significant difference. A 16mm screw is much more resistant to "whipping" (deflection) over longer spans.

If your axis travel is >300mm, the 1605 is highly recommended to prevent vibration during fast movements.
For very small machines (e.g., 200mm travel), the 1204 provides sufficient rigidity and its smaller nut size helps save precious build space.

2. Stepper Motor Torque Curves

Stepper motors lose torque as RPM increases.

The 1605 Advantage: To reach a cutting speed of 2500 mm/min, a 1605 screw only needs 500 RPM.
The 1204 Challenge: To reach the same speed, a 1204 screw needs 625 RPM.

If your motor's torque drops off sharply after 500 RPM, the 1605 will actually perform better and more reliably at high feed rates.

3. Acceleration and "First Gear" Advantage

As noted by experienced builders, 1204 screws offer better mechanical advantage. It is like driving in 1st gear versus 2nd gear. The 1204 will accelerate a heavy gantry more easily, but it will "run out of steam" at top speeds sooner than the 1605.

Axis-by-Axis Recommendation

X & Y Axis (The Workhorses)

For most small CNC routers (cutting wood or soft metals), 1605 is the safer choice. It handles the weight of the gantry and the lateral cutting forces with less deflection. However, if you are building a machine primarily for PCB milling or jewelry engraving where space is at a premium, 1204 is more than adequate.

Z Axis (The Precision Axis)

The Z-axis often has the shortest travel. Because the load is vertical and the travel is limited, a 1204 ball screw is an excellent choice here. It saves weight and provides the fine resolution needed for precise depth control.

Which Should You Choose?

Choose 1204 Ball Screw If:

Your machine travel is very short (under 250mm).
Installation space for the ball nut is extremely tight.
You are building a high-precision, light-duty machine (PCB, wax, laser).
You need to minimize the rotating inertia for very fast accelerations.

Choose 1605 Ball Screw If:

You have a heavier spindle (e.g., 1.5kW or 2.2kW).
You plan to cut wood at high feed rates (needing better RPM-to-speed ratios).
Your axis travel exceeds 300mm.
You want a more common size that is easy to replace or upgrade later.

Procurement Checklist for B2B Buyers

When sourcing these components, don't just look at the diameter. To ensure a successful build or high-quality product line, confirm the following:

Nut Profile: Does the 1605 nut fit within your gantry plates? 1605 nuts are noticeably larger than 1204.
Accuracy Grade: Are you buying C7 (standard) or C5 (precision ground) screws?
End Machining: Ensure the ball screw ends are machined to match standard BK12/BF12 (for 1605) or BK10/BF10 (for 1204) support units.
Compatibility: Confirm the coupling bore size matches your stepper motor shaft (e.g., 8mm or 6.35mm).

Conclusion

In the battle of 1204 vs 1605 ball screws, the "better" choice is the one that matches your machine's rigidity needs and your motor's capabilities. For a robust, versatile small CNC router, 1605 is the industry favorite for its balance of speed and strength. For ultra-compact, precision-focused builds, the 1204 offers a lightweight and space-saving alternative without sacrificing accuracy.

Still not sure? Contact our technical team with your machine's travel length and spindle weight, and we will help you calculate the optimal ball screw size for your project.