Calculating Feeds and Speeds
Before setting up any file for cutting, certain parameters must be considered in order to achieve the desired finish and accuracy. Chief among these is Chipload per Tooth (CPT), which is the size or thickness of the chip removed by each flute per revolution. To determine the optimal CPT, a variety of factors must be taken into account, including the power and rigidity of the machine, the hold-down of the part being machined, spindle horsepower, cut depth and width, tool sharpness, cutter type, and the material being cut.
The feed rate and RPM, (Feed and Speed) should be set in the CAM software used to create the toolpath to cut. On this page you find tools to aid in choosing the appropriate settings for a given material/router bit combination, but these may need to be adjusted through a process of trial and error.
Most controllers can be used to adjust both the feed and speed at while the program is running, and by listening to the sound the cutter makes, one can often optimize the given parameters. It is also important to note that chips should be created instead of dust, as this will help to remove heat from the cutting process, thus extending tool life and improving edge quality.
When determining the feed rate and machining direction for a project, it is usually suggested to start off with a feed rate that is approximately one-half the calculated amount and gradually increase it to the capacity of the machine and the finish desired.
Direction of cut for woods will usually be conventional milling or cutting forward, and the depth of cut should not be greater than twice the radius of the bit. For Aluminium, the depth should be less or equal to the radius of the cutter and climb milling could be used to achieve a good finish.

Average Chipload
Below you find an average of the suggested chipload per tooth (CPT) per material and bit size. You can use these values in the Feeds and Speeds Calculator.
Diameter
3 mm
4 mm
6 mm
8 mm
10 mm
12 > mm
Hardwood
0.08 – 0.13
0.15 – 0.22
0.23 – 0.28
0.28 – 0.38
0.38 – 0.46
0.48 – 0.53
Soft / Ply
0.1 – 0.15
0.15 – 0.25
0.28 – 0.33
0.35 – 0.40
0.43 – 0.51
0.53 – 0.58
MDF
0.10 – 0.18
0.20 – 0.30
0.33 – 0.41
0.40 – 0.50
0.51 – 0.58
0.64 – 0.69
Plastics
0.15 – 0.20
0.20 – 0.25
0.25 – 0.30
0.25 – 0.30
0.25 – 0.30
0.30 – 0.41
Aluminium
0.05 – 0.10
0.07 – 0.12
0.08 – 0.15
0.09 – 0.18
0.10 – 0.20
0.20 – 0.25
Supplier Feeds and speeds
Best sources for feeds and speeds are from the suppliers. However, not all suppliers have it available, or are specified to the limitations of the RatRig Killerbee and OpenBuilds machines.
Spetool Feeds & Speeds
This page by Spetool gives handouts for Feeds and Speeds of their bits. Unfortunately doesnt include a lot of Metric sizes
Spetool Tool Libraries
This page by Spetool has tool libraries to load their bits in Fusion360, Vectric & Carveco. Unfortunately not all Metric sizes are included.
Calibrating Feeds & Speeds
This page by Precisebits gives a lot of insight on how to calculate your feeds and speeds
Bit Types
Upcut
Downcut
Compression
Straight

Upcut bits
Pros
- Upcut spiral clears chips from the kerf, allowing for faster feed rates and deeper cuts
- Cleaner bottom of cut
- Great for pockets
- Great for MDF (less loose fibers), Plastics, Aluminium, or material of which heat buildup is concerning
- Can use higher Feeds and Speeds
Cons
- Upcut pulls upwards, causing chipped or frayed top face.
- Upwards force may cause part being lifted of spoilboard.
- Not well suited for Plywood

Downcut bits
Pros
- Downcut spiral pushes chips down into the cut, leaving crisp top edges
- Downward force helps with cutting thin sheets
- Great for 2D pocket cuts
- Great for Plywood, Laminates, MDF, Hardwood, Softwood
Cons
- Chips or fray bottom face when through-cutting (less applicable for CNC because of underlaying spoilboard)
- Chips being pushed down can fill up the cut.
- Requires slower feedrates

Compression bits
Pros
- Combines Pros of UP& Down Cuts
- Cleaner bottom of cut
- Clean edges on top and bottom face
- Great for 2 D Profile cuts
- Great for Plywood, Laminates, MDF, Hardwood, Softwood
- Can use higher Feeds and Speeds
Cons
- Make sure the bit length fits the cut depth to fully suit UP and DOWN cut profile of bit

Straight bits
Pros
- Good edge quality on most materials
- Moderate chip clearing ability
- Fits most materials
Cons
- Lower processing efficiency than spiral bits
- More heat buildup
- Need use lower Feeds and Speeds
My Bits
Here’s a list of the bits I like to use and why. All bits here are in my personal collection. Bits that failed on me will be removed.
As always; this list is just my personal recommendation; If you have a suggestion or question, just ask.
Regular
Tapered
Engraving
Other

SpeTool 8MM UpCut bit
- ID:
- Shank Ø: 8 MM
- Cutter Ø: 8 MM
- Flute Length: 32 MM
- Total Length: 75 MM
- Composition: Carbide
- Great for: 2D profiling and Pocketing.
- Materials: Oak, MDF, Hardwood, Softwood

SpeTool 4MM Compression Bit
- ID: SP2FC-D4-L25
- Shank Ø: 4 MM
- Cutter Ø: 4 MM
- Flute Length: 25 MM
- Total Length: 50 MM
- Composition: Carbide
- Great for: 2D profiling and Pocketing.
- Materials: Oak, MDF, Hardwood, Softwood

SpeTool 6MM Compression Bit
- ID: SP2FC-D6-L32
- Shank Ø: 6 MM
- Cutter Ø: 6 MM
- Flute Length: 32 MM
- Total Length: 75 MM
- Composition: Carbide
- Great for: 2D profiling and Pocketing.
- Materials: Oak, MDF, Hardwood, Softwood

SpeTool 8MM Compression Bit
- ID: SP2FC-D8-L45
- Shank Ø: 8 MM
- Cutter Ø: 8 MM
- Flute Length: 45 MM
- Total Length: 100 MM
- Composition: Carbide
- Great for: 2D profiling and Pocketing.
- Materials: Oak, MDF, Hardwood, Softwood

Fraisertools 4MM Downcut Bit
- ID: 303.040.6D
- Shank Ø: 6 MM
- Cutter Ø: 4 MM
- Flute Length: 15 MM
- Total Length: 60 MM
- Composition: Carbide
- Great for: Pocketing, Laminates, Plywood, Painted surfaces.
- Best finish on the UPPER side of the panel
- Materials: Oak, MDF, Hardwood, Softwood

SpeTool r 1.0mm Tapered Ball Nose
- ID: R1X30.5XD6-3.8
- Shank Ø: 6 MM
- Tip Ball Radius: 1 MM (Ø: 2 MM)
- Taper: 3.8°
- Flute Length: 30.5 MM
- Total Length: 75 MM
- Composition: H-Si coated Carbide
- Great for: 2D and 3D profiling and carving. The high-shear ball nose tips cut smooth 2D and 3D contours with reduced stepping.
- Materials: Oak, MDF, Hardwood, Softwood, Aluminium, Copper, Brass

4Pcs SpeTool r 0.25-1mm Tapered Ball Nose
- ID: 0792276837205
- Shank Ø: 4 MM
- Tip Ball Radius: 0.25 – 1 MM (Ø: 2 MM)
- Taper: 4.9°, 4.2°, 3.5°, 2.8°
- Flute Length: 20.5 MM
- Total Length: 50 MM
- Composition: TiAIN coated Carbide
- Great for: 2D and 3D profiling and carving. The high-shear ball nose tips cut smooth 2D and 3D contours with reduced stepping.
- Materials: Oak, MDF, Hardwood, Softwood

SpeTool V-bit 30° for Engraving
- ID: D6-30-0.2
- Shank Ø: 6 MM
- Tip Ø: 0.2 MM
- Flute Length: 10 MM
- Total Length: 50 MM
- Carbide
- Used for: Sign Making, Engraving
- Great for: Oak, MDF,HDF, Hardwood, Softwood, Acrylic, Plastics, Composites

SpeTool V-bit 60° for Engraving
- ID: ECP3F-D6.0-R60
- Shank Ø: 6 MM
- Tip Ø: 0 MM
- Flute Length: 5.2 MM
- Total Length: 50 MM
- TiAIN Coated Carbide
- Used for: Sign Making, Engraving, Chamfering
- Great for: Oak, MDF,HDF, Hardwood, Softwood, Acrylic, Plastics, Composites

SpeTool V-bit 90° for Engraving
- ID: ECP3F-D6.0-R90
- Shank Ø: 6 MM
- Tip Ø: 0 MM
- Flute Length: 3 MM
- Total Length: 50 MM
- TiAIN Coated Carbide
- Used for: Sign Making, Engraving, Chamfering
- Great for: Oak, MDF,HDF, Hardwood, Softwood, Acrylic, Plastics, Composites

Bosch V-bit 60° for Engraving
- ID: 2 608 628 406
- Shank Ø: 8 MM
- Tip Ø: 0 MM
- Flute Length: 13.7 MM
- Total Length: 45 MM
- TiAIN Coated Carbide
- Used for: Sign Making, Engraving, Chamfering
- Great for: Deeper cuts, Chamfering
- Rating: Dulls easily

SpeTool 35MM Flattening Bit
- ID: IP3F-D35-H8
- Shank Ø: 8 MM
- Tip Ø: 35 MM
- Cutter Length: 10.5 MM
- Total Length: 75 MM
- Carbide
- Used for: Spoilboard flattening; Facing pass of workpiece
- Materials: Oak, MDF,HDF, Hardwood, Softwood

Spare cutters for 35MM Flattening Bit
- ID: IPA-D10.5-H2.2
- Cutter Length: 10.5 MM
- Thickness: 2 MM
- TiAIN Coated Carbide
Disclaimer
Links on this page are in most cases Amazon Affiliate links. When ordering through these link, I may receive a fee for this, without it costing you anything extra. Any discounts still remain valid. I have no traceable information that can link orders to your account.
Information stated is in no way a guarantee this will work on your CNC. Ratrig machines, or any OpenBuilds machines, are DIY builds and therefor it is impossible to guarantee a fit. This list is purely a collection of my own used bits, combined with found information online.