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CNC feeds and speeds
Starting values for Grbl machines with spindles up to about 800 W. The table shows a common bit for each material, the material pages list all 175 bits in the catalogue.
Starting values at a glance
| MaterialReference bit | SpeedRPM | Feedmm/min | Plungemm/min | Depthmm | Chip loadmm |
|---|---|---|---|---|---|
| SoftwoodEnd mill Ø 3.175 mm · 2 flutes · upcut | 18,000 | 1,140 | 340 | 1.6 | 0.032 |
| HardwoodEnd mill Ø 3.175 mm · 2 flutes · upcut | 18,000 | 860 | 260 | 1.1 | 0.024 |
| PlywoodEnd mill Ø 3.175 mm · 2 flutes · upcut | 18,000 | 970 | 290 | 1.25 | 0.027 |
| MDFEnd mill Ø 3.175 mm · 2 flutes · upcut | 18,000 | 1,090 | 330 | 1.6 | 0.03 |
| Rigid foamEnd mill Ø 3.175 mm · 2 flutes · upcut | 16,000 | 1,630 | 650 | 3.15 | 0.051 |
| AcrylicEnd mill Ø 3.175 mm · 2 flutes · upcut | 16,000 | 810 | 240 | 0.95 | 0.025 |
| PlasticsEnd mill Ø 3.175 mm · 2 flutes · upcut | 16,000 | 1,120 | 340 | 1.6 | 0.035 |
| AluminiumEnd mill Ø 3.175 mm · 2 flutes · upcut | 12,000 | 270 | 50 | 0.3 | 0.011 |
| BrassMulti-flute end mill Ø 3.175 mm · 3 flutes · ZrN coated | 10,000 | 290 | 60 | 0.25 | 0.01 |
| Circuit boardCorn cob bit Ø 2 mm | 20,000 | 180 | 50 | 0.5 | – |
Starting values without guarantee. Machine, spindle, clamping and bit condition all affect the right values.
The terms
- Spindle speed (n)
- Revolutions of the spindle per minute (RPM). Small bits need high speeds, large ones lower speeds.
- Feed rate (f)
- How fast the bit moves sideways through the material, in mm/min.
- Plunge rate
- Speed when moving straight down. Bits cut poorly downwards, so it is lower.
- Depth of cut (ap)
- How deep the bit cuts per pass. Deep pockets take several passes.
- Stepover (ae)
- When clearing pockets: how far two passes overlap, as a percentage of the bit diameter.
- Chip load (fz)
- How thick a chip each flute takes: feed ÷ (speed × flutes). Too small: rubbing and heat; too large: risk of breaking.
Tuning the values for your machine
- Start with the given values and change the feed rate in steps of 10 to 20 %, the spindle speed only after that.
- Good chips are small curls or flakes. Fine dust and burn marks mean: raise the feed rate or lower the speed.
- If the bit squeals or chatters, reduce the depth of cut and clamp the bit shorter.
- Light machines with aluminium extrusion frames often only take half the depth of cut; the feed rate can stay the same.
Frequently asked questions
What spindle speed for wood on a CNC router?
For a 3.175 mm two-flute end mill, 18,000 RPM is a good start in softwood, 18,000 RPM in hardwood with a lower feed rate.
What feed rate for MDF?
With the same bit about 1,090 mm/min at a depth of 1.6 mm. MDF takes high feed rates because it is uniform.
Can a hobby CNC cut aluminium?
Yes, with a light depth of cut (about 0.3 mm), lubrication and a single-flute or coated bit. A rigid setup matters most.
Why does the wood burn when routing?
The bit is rubbing instead of cutting: the feed is too low or the speed too high, or the bit is dull. Raise the feed rate first.
The app applies the values
In CNC.myWerkzeug.de you choose the material and the bit, and the matching feeds and speeds are already in the toolpaths. You can save your own values per bit.