35
🧵 Understanding the Ball Screws Used in Your PwnCNC Dominator Machine
What does “C7 grade rolled ball screw” mean, and why did we choose it?
At PwnCNC, we carefully select components that strike the right balance of performance, reliability, and value for our customers. One of the key mechanical components in any CNC machine is the ball screw, which directly affects accuracy, smoothness, and motion efficiency.
All of our machines use C7 grade rolled ball screws — here’s what that means and why it matters to you.
⚙️ What Is a Ball Screw?
A ball screw is a high-efficiency mechanical drive that converts rotary motion into linear motion. It consists of a threaded shaft (the screw) and a nut that contains recirculating ball bearings, which reduce friction and allow for smoother and more accurate movement compared to standard leadscrews.
Ball screws are commonly used in CNC machines to drive the X, Y, and Z axes.
🏗️ Rolled vs Ground Ball Screws
There are two main manufacturing methods for ball screws:
| Type | Rolled Ball Screw | Ground Ball Screw |
|---|---|---|
| Process | Formed by cold-rolling the thread into the shaft | Precision ground with a grinding wheel |
| Cost | Lower | Higher |
| Accuracy | Good for most CNC uses | Ultra-high precision |
| Lead Variation | Slightly more than ground | Very minimal |
Â
Rolled ball screws like ours offer excellent performance for hobby and semi-pro CNC work, without the high cost of ground screws used in aerospace and high-end industrial machines.
🧠What Does "C7 Grade" Mean?
Ball screws are classified by lead accuracy grades under the ISO 3408 standard. These grades tell you how closely the screw’s movement matches the expected travel per revolution.
For C7 grade, the tolerance is:
±50 microns (0.050 mm) per 300 mm of travel.
This means that over a 300 mm (about 12 inch) move, the nut will land within ±0.050 mm of the commanded position — and that’s before any correction from the motion control system.
Comparison of Grades:
| Grade | Accuracy (per 300 mm) | Typical Use |
|---|---|---|
| C3 | ±7 µm | Ultra-precision industrial |
| C5 | ±23 µm | High-end CNC |
| C7 | ±50 µm | Hobby and semi-pro CNC |
| C10 | ±210 µm | General automation |
🛠️ Why C7 Rolled Ball Screws Are the Right Fit
We use C7 rolled screws because they offer:
-
âś… Plenty of accuracy for wood, plastics, and aluminum jobs
-
âś… Smooth motion with minimal backlash
-
âś… High load capacity and long life
-
âś… Excellent value without inflating machine cost
-
âś… Perfect compatibility with closed-loop steppers that correct minor deviations on the fly
For the type of CNC work most of our customers do — from cabinetry to aluminum part making — C7 accuracy is more than enough, especially when paired with our closed-loop stepper systems.
🎯 Real-World Accuracy
In a typical machine like the Dominator, the combination of C7 ball screws and closed-loop steppers results in:
-
Repeatable moves within ±0.01 mm
-
Consistent cuts without “drift”
-
Long-term reliability with proper lubrication and maintenance
🧠Summary
A C7 grade rolled ball screw is the CNC industry’s sweet spot for performance and value. It gives you accurate, smooth, and repeatable motion with a long service life — and at a price that makes sense for small shops, prosumers, and serious hobbyists.
Still have questions about precision or machine specs? Contact us here — we’re happy to help.
