Spindle, VFD, and coolant system
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Spindle - VFD - Coolant system
The spindle is the beefy rotary tool we use to cut through materials. It uses a special type of tool called an end mill, which, despite appearances, is technically not a drill bit. Drill bits are sharpened in a way that allows them to cut through material vertically, while end mills are made to cut better horizontally. It's very common to still call end mills "bits" during conversations, but the distinction is very important.
WARNING: Do not use ordinary drill bits with the spindle! Best case scenario is you break your bit. Worst case scenario is you break our lovely (expensive) spindle.
Our spindle came to us from China with no branding or model number, which is typical of these generic low-cost CNC bundles. Luckily, these spindles are widely used and surprisingly high regarded within the hobbyist CNC community, which means there is a good amount of informal documentation in the form of blog posts and forum threads out there. While we may not have an explicit manual with all of the specifications we'd like, a quick Google search for "2.2kw chinese spindle" should yield helpful results for whatever you'd like to know.
- Power rating (kW) = 2.2 kW
- Collet size = ER20
- Max speed (RPMs) = 24,000 RPM
- Type of cooling = Liquid
- Runout = Less than 0.001mm (what is runout?)
The VFD, or variable-frequency drive, is the device that directly controls the spindle and allows for variable control of its speed. It does this by manipulating the frequency of the AC signal that is used to power the spindle.
Whereas we are normally used to seeing about 60 Hz in ordinary wall power, this device is able to wiggle the AC signal at anywhere between 0 and 400 Hz, corresponding to lower or higher RPMs in the spindle.
This frequency can be controlled manually via the physical interface of the device, or electronically via an analog signal connected to one of its terminals. We currently have this terminal connected to the 7i76 board, which allows LinuxCNC to output a signal to directly control the spindle speed as needed.
- Make/model = Huanyang HY02D223B
- Input voltage = Single and three phase 220V
- Power output = 2.2 kW
- Inverter capacity = 4.4 kVA
- Output current = 11 A
- Output frequency range = Up to 400 kHz
- We are currently supplying the VFD with 240V, two phase power via a twist-to-lock socket and plug.
- We are currently controlling spindle speed by connecting the V1 terminal to the pin 2 (SPINDLE OUT) on header TB4 of the 7i76. LinuxCNC sends an analog voltage through this pin by way of the 5i25.
[TODO: document wiring schema]
| VFD pin | XLR pin |
|---|---|
| U | |
| V | |
| W |
- Download the manual from /docs/spindle-and-coolant-system/
Cutting through material generates a lot of heat in the spindle, as does the sheer electrical power needed to keep it spinning under load, so we need to continuously pump liquid through it to transport the heat away. To do this we have a coolant pump sitting in a 5 gallon bucket filled with windshield washer fluid, which gets pumped to the spindle through one tube and returns back to the bucket through another tube.
WARNING: Do not use the spindle to cut any material until you've turned on the coolant pump and made sure its working! You wouldn't want our fancy, expensive spindle to melt and/or start a fire!
- Make/model = Ding Sheng DS-3500
- Flow rating (gph) = 800 gph, or 3000 lph
- Maximum height = 3.5m, or 11.5ft
- Power requirements = 220V, 75W
- Material?
- Inner and outer diameters?
We use windshield washer fluid as the coolant for it's antibacterial properties, low cost, ubiquity, and coloring.
Plain old water can easily harbor bacteria that grow over time, which is certainly not something you want to have happening inside of an expensive spindle. Tap water also contains lots of minerals, which can build up and potentially corrode internal components.
Windshield washer fluid is super cheap and available just about anywhere, so no one needs any special knowledge to keep it topped off.
Finally, it's blue color makes spotting leaks and flow super easy. It's like our machine has blue blood that we can see flowing when its working!