Student Material 001: Feeds, Speeds & Toolpath Quick Reference¶

Material ID: U4M2-MAT-001 Purpose: Quick reference for CNC routing parameters, tool selection, and toolpath configuration Updated: 2026-03-19

Chip Load Formula¶

Feed Rate (IPM) = Chip Load × RPM × Number of Flutes
Chip Load = Feed Rate ÷ (RPM × Number of Flutes)

Recommended Chip Loads (inches per tooth)¶

Material	⅛" 1-Flute	⅛" 2-Flute	¼" 1-Flute	¼" 2-Flute	¼" 3-Flute
Softwood (pine)	0.003–0.005	0.002–0.004	0.005–0.007	0.003–0.005	0.003–0.004
Hardwood (oak/maple)	0.002–0.004	0.002–0.003	0.004–0.006	0.003–0.005	0.002–0.004
Plywood	0.002–0.004	0.002–0.004	0.005–0.007	0.003–0.005	0.003–0.004
MDF	0.002–0.004	0.002–0.004	0.005–0.007	0.003–0.005	0.003–0.004
Cast Acrylic	0.003–0.005	0.002–0.004	0.004–0.006	0.003–0.006	N/A*
Extruded Acrylic	0.002–0.004	0.001–0.003	0.003–0.005	0.002–0.004	N/A*
HDPE	0.003–0.006	0.003–0.005	0.005–0.008	0.004–0.007	N/A*
Delrin/POM	0.003–0.005	0.002–0.004	0.004–0.007	0.003–0.006	N/A*
Aluminum 6061	0.001–0.002	0.001–0.002	0.002–0.003	0.001–0.003	0.001–0.002
Foam (rigid)	0.005–0.010	0.005–0.010	0.010–0.020	0.010–0.020	0.008–0.015

*N/A: Avoid multi-flute tools in plastics — chips clog flutes, causing heat buildup and melting.

Stepdown (Depth per Pass) Guidelines¶

Material	Stepdown (% of tool diameter)	Example: ¼" tool
Softwood	75–100%	0.1875"–0.25"
Hardwood	50–75%	0.125"–0.1875"
Plywood/MDF	50–100%	0.125"–0.25"
Acrylic	50–75%	0.125"–0.1875"
HDPE/Delrin	75–100%	0.1875"–0.25"
Aluminum	25–50%	0.0625"–0.125"
Foam	100–300%	0.25"–0.75"

Stepover Guidelines¶

Operation Type	Stepover (% of tool diameter)
Roughing pocket	40–60%
Finishing pocket	5–15%
3D roughing	40–50%
3D finishing (ball nose)	5–15%
Profile (single pass width)	N/A — follows contour

Toolpath Type Selection Guide¶

What are you cutting?
│
├── Along an edge/outline → PROFILE
│   ├── Cutting out a part → Outside profile
│   ├── Cutting a hole → Inside profile
│   └── Engraving a line → On-line profile
│
├── Clearing an area to a depth → POCKET
│   ├── Simple rectangle/circle → Standard pocket
│   ├── Complex shape → Adaptive clearing
│   └── Text/logo recess → Pocket with island
│
├── Making holes → DRILL
│   ├── Hole = tool diameter → Simple drill cycle
│   ├── Hole > tool diameter → Helical bore or pocket
│   └── Deep hole (>3× diameter) → Peck drill cycle
│
├── Decorative text/design → V-CARVE
│   └── Variable-depth beveled cut using V-bit
│
└── 3D surface/relief → 3D CONTOUR
    ├── Rough with flat end mill, finish with ball nose
    └── Use small stepover for smooth finish

Tool Selection Quick Reference¶

Tool Type	Best For	Avoid Using For
Upcut spiral	General cutting, deep pockets	Top-surface finish (causes tearout)
Downcut spiral	Clean top surface, thin material	Deep pockets (poor chip evacuation)
Compression	Plywood through-cuts (clean both faces)	Shallow cuts (not both geometries engaged)
Single flute (O-flute)	Plastics, aluminum	Hardwood roughing
Ball nose	3D contour finishing	2D profiles, flat pockets
V-bit (60°/90°)	V-carving, chamfers, engraving	Through-cuts, deep pockets
Straight flute	Composites, laminates	General routing (less efficient)

Common G-Code Reference¶

Code	Function	Example
G0	Rapid move (max speed, no cutting)	G0 X0 Y0 Z1.0
G1	Feed move (controlled speed, cutting)	G1 X5.0 F100
G2	Clockwise arc	G2 X1 Y0 I0.5 J0 F80
G3	Counter-clockwise arc	G3 X1 Y0 I0.5 J0 F80
G17	XY plane selection	G17
G20	Inch units	G20
G21	Millimeter units	G21
G28	Return to home	G28
G54	Work coordinate system 1	G54
G90	Absolute positioning	G90
G91	Incremental positioning	G91
M3	Spindle on (clockwise)	M3 S18000
M5	Spindle off	M5
M8	Coolant on	M8
M9	Coolant off	M9
M30	Program end & reset	M30

Pre-Cut Verification Checklist¶

[ ] Correct post processor selected for machine
[ ] Units match (design and G-code both inches OR both mm)
[ ] Simulation completed — no collisions
[ ] Tabs added on all through-cut profiles
[ ] Retract height clears all clamps and fixtures
[ ] Feeds and speeds calculated (not guessed)
[ ] Operations ordered: interior features before exterior profiles
[ ] Tool matches what is physically installed in the spindle

Last Updated: 2026-03-19