Short answer
There is no single fixed measurement. The correct height depends on your spoilboard thickness, tooling, dust boot, and accessories.
Recommended starting point
Set the spindle so that with the Z-axis fully lowered, the collet or collet nut (with no bit installed) just touches the spoilboard (or a known-thickness sacrificial board).
This gives a reliable baseline that:
- Lets short tools reach the work surface
- Preserves as much usable Z travel as possible
- Works for most standard setups
Why there isn’t a “magic number”
Every setup is different:
- Spoilboard thickness varies
- Tool lengths vary
- Dust boots, ATCs, and fixtures take space
Because of this, neither Redline CNC nor Onefinity CNC specifies an exact dimension.
When you might adjust it
You may want to raise or lower the spindle slightly if:
- You frequently use very short cutters
- You’re running a dust boot that needs more clearance
- You’re using an ATC or tool setter that affects Z travel
The goal is always the same:
Shortest tool reaches the work at the bottom, without sacrificing unnecessary Z travel at the top.
What to avoid
- Don’t mount the spindle excessively low — you’ll lose usable Z travel.
- Don’t mount it so high that short tools can’t reach the spoilboard.
Simple setup checklist
- Place a scrap board on the spoilboard
- Lower Z fully
- Install the collet and nut (no bit)
- Slide the spindle down until the collet/nut just touches the board
- Tighten the spindle mount
- Test with your shortest cutter and adjust if needed
Bottom line:
Set it once using the “touch the spoilboard” method, then fine-tune based on your tooling and accessories.