Chip evacuation
Chips carry heat out of the cut. If they stay in the cut, the bit cuts them again, which adds heat without removing material, dulls the edge and can pack solid enough to break the tool. Deep slots and pockets in soft or sticky material are where it goes wrong.
Chips are how heat leaves
Cutting turns energy into heat, and most of that heat should leave with the chip. A chip that stays in the cut has already absorbed its heat and is now sitting next to the tool, being cut again and heating up further. Three things follow:
- Heat builds in the cut. Which burns wood, melts plastic and dulls carbide.
- The tool does work it gets nothing for. Recutting chips uses power and edge life to remove material that was already removed.
- Packed chips exert real force. Tightly packed flutes can seize a bit in a slot, and that is a broken tool.
Where it goes wrong
| Situation | Why it is bad | What helps |
|---|---|---|
| Deep slot, full width | Chips have nowhere to go but up the flutes | Fewer flutes, upcut bit, shallower passes, peck or ramp |
| Deep pocket, downcut bit | The bit is actively packing chips downward | Rough with an upcut, finish with a downcut |
| Plunging a blind hole | Closed bottom, nothing can escape sideways | Helical entry, or drill it properly |
| Soft resinous pine | Chips are sticky and clump | Sharp bit, higher feed, good dust extraction |
| Acrylic | Chips melt and weld back into the cut | Single flute, faster feed, lower RPM, air blast |
| Dust shoe with no airflow | Vacuum blocked or hose too small | Check the filter and the hose diameter |
The tools you have for it
- Bit choice. An upcut spiral lifts chips out actively, and it is the right choice whenever clearing matters more than the top edge. Fewer flutes means bigger gullets.
- Dust collection at the tool. A dust shoe that actually pulls air at the cut does more than any setting change. See dust collection.
- Air blast. A small stream of compressed air aimed at the cut is standard practice in plastics and helps in deep wood slots. Keep it low pressure so you are not blasting dust into the room.
- Toolpath strategy. Ramping instead of plunging, pecking deep holes, and clearing a pocket with a lighter stepover before profiling the walls.
- Feed rate. Counterintuitively, feeding faster often helps: bigger chips are easier to evacuate than dust, and they carry more heat per chip.
The dust shoe tradeoff
A dust shoe is the single best chip evacuation tool you have, and it also hides the cut from you. On unfamiliar material, run the first test cut with the shoe off or the brush lifted so you can see and hear what is happening. Once you know the settings work, put it back.