Spindle Types#
We’ll do a quick overview of the different spindle options and how they can be controlled.
Here you can see side by side a 400W DC spindle, a 1.25HP trim router, and an 800W water-cooled VFD spindle.
DC motor#
Most hobby-level machines come out of the box with a simple DC spindle. Such DC motor spindles are often underpowered and have low-quality bearings.
A DC spindle can be turned on and off via G-code. This is handled by a relay inside the control box that connects the DC voltage from the power supply to the spindle output.
The speed is controlled manually via a knob on the power supply that directly changes the voltage from zero to max level. You can’t change it programmatically from G-code.
Trim router#
You can use an off-the-shelf trim router as a spindle. They are inexpensive, but are not intended for prolonged continuous use. Expect them to wear out or burn out at some point.
In the simplest of cases you can plug in the router directly to AC power, and manually turn it on/off when needed.
If you wish to start the router from G-code, you need to use a device called “smart relay”. You plug the relay into an AC outlet and plug the router into the relay. The relay then connects and disconnects the power using signals from the control box.
A common way to connect the relay is by using the output for the DC spindle. When the G-code tries to turn on the spindle, it will activate the relay instead.
Warning: When using the DC spindle output to control a smart relay, keep in mind that the relay requires certain voltage to turn on. If the voltage is too low, the relay will not turn on. If the voltage is too high, the relay may burn out. Adjust the voltage using the DC spindle speed knob to the necessary level.
For speed control you are limited to the capabilities of the router. Often routers have a dial for changing the speed manually. You do that before you start the program.
VFD spindle#
A VFD spindle is both mechanically and electrically superior to the other options. Such a spindle has better bearings with less runout and can run for longer without overheating. It is also significantly quieter, especially if it is water-cooled.
A VFD spindle has two components - the VFD (Variable Frequency Drive) and the spindle motor itself. The VFD generates a 3-phase current for the motor at a frequency, necessary to achieve the requested RPMs.
Most VFDs can be controlled in one of 3 ways:
- Manual: You turn on the spindle and select the speed using buttons on the VFD itself
- DC voltage: You can change the speed using a DC voltage level, usually in the range of 0-5V or 0-10V
- RS485 protocol: RS485 is a serial protocol that can be used to control the speed and direction of the spindle
The DC voltage and RS485 outputs are only found on the more advanced and expensive Grbl control boards. Most commonly you will only find a PWM (Pulse Width Modulation) output that is intended to modulate the laser power when doing engraving. A common way to connect a VFD is to use a PWM to DC converter. Some VFDs have a built-in converter and thus can directly connect to the PWM output.
Here’s a tutorial on how you can use a PWM converter to control a VFD spindle. Adding a VFD for a Spindle
Note: When you control the spindle speed from G-code, you need to make sure the Grbl settings are correct. More on that here: Spindle speed settings