CNC Crash Course #5 – The REAL Reason Your Spindle Is Stuck at One Speed
🎥 Video
📝 Overview
This lesson tackles one of the most common beginner CNC frustrations: the spindle only runs at one speed no matter what S‑value you enter. Many new GRBL users assume their machine is broken, but the real issue is almost always a wiring or controller‑capability mismatch.
The video demonstrates why GRBL machines behave this way, how PWM spindle control actually works, and what you need to check to unlock full variable‑speed control.
📌 What You’ll Learn
- Why your spindle ignores S‑commands like
S5000orS12000 - How PWM spindle control works on GRBL machines
- The difference between M3 (spindle on) and M3 Sxxxx (spindle + speed)
- How to check whether your controller supports PWM
- Why some 3018‑style CNCs ship with fixed‑speed spindles
- What to upgrade if you want true variable‑speed control
📂 Tools & Software Used
- 3018‑style CNC router
- Candle (GRBL Control)
- GRBL controller board (varies by model)
- Standard ER11 spindle or aftermarket PWM‑capable spindle
📘 Description
This lesson explains why many beginner CNC routers appear to ignore spindle speed commands. GRBL uses PWM (pulse‑width modulation) to control spindle RPM, but not all controllers or spindles support it. Some machines only accept a simple on/off signal, which forces the spindle to run at a single fixed speed. The video shows how to test your machine, what to look for on your controller board, and how to determine whether your spindle supports PWM speed control.
💡 Key Takeaways
- A spindle stuck at one speed is usually caused by non‑PWM wiring or a non‑PWM spindle.
- GRBL expects a PWM‑capable controller to interpret S‑values.
- Many budget CNCs ship with fixed‑speed spindles that cannot change RPM.
- Upgrading the spindle or controller unlocks full speed control.
- Understanding PWM helps you troubleshoot future spindle issues.