¶ Selecting a Bit
- The bit[1] you select is critical to getting the best cut. It attaches to the spindle[2] with a chuck[3] and collet[4], which are sized to match the bit.
- Bit size is often labeled on the shank[5], or can be measured with calipers.
Members are responsible for supplying their own bits.
Chucks and collets can be found in the Digital Fabrication tool cabinet.
¶ Skills/Class Required
- A membership or day pass is required to access Digital Fabrication.
- CNC Router 1 Shop Safety is required to use the ShopBot CNC Routers.
- CNC Router 2: Laguna is required to use the Laguna CNC Router.
¶ Things to Consider
These three factors are key to determining the right bit for the job:
- Size of the shank.
- Type of material.
- Level of detail.
¶ CNC Router Bits
¶ Bit Material
¶ End Mills
- A rotating cylindrical cutting tool with teeth at its end.
- Can cut in any direction
- Used for shaping the face and sides of a workpiece.
- Mills have one or more cutting edges.
- A drill bit can be considered a mill with a pointed end that cuts only in its axial direction.
¶ Types of End Mills (Spiral Cut Router Bits)
- Flat Tip: Bit ends with a flat surface at the tip.
- Ball-Nose Spiral: Rounded end bits used for 3D carving and smooth contours.
- Cove Spiral: Similar to a ball nose spiral, with a flat end bit instead of a rounded end bit.
- V-Groove (Lettering): Carves sharp grooves used for lettering and smooth contours.
¶ Flute Types
- Straight Flute: A straight flute is parallel to the shank. A straight bit is stronger than a spiral bit and can cut material at higher speeds. A straight flute bit is a great all around bit with decent chip removal, but they produce a less smooth surface finish.
- Spiral Flute: A spiral shaped flute along the shank. A spiral flute makes constant contact with the material surface. Spiral flute bits can achieve a smoother surface finish, but a spiral flute bit cannot plunge as deeply, or cut as quickly, as a straight flute bit.
- Upcut Spiral Flute: Spirals wrap around the body of the bit clockwise, pulling chips away from the material being cut. Upcut bits tend to leave a rough surface finish, with a smoother finish on the bottom of the workpiece. Upcut bits have great chip removal, but they can tear-out the top of thin veneer such as finish grade plywood.
- Downcut Spiral Flute: Spirals wrap around the body of the bit counterclockwise, pushing chips down as it's cutting. Downcut bits leave a smooth surface finish, with a rougher finish on the bottom of the workpiece. Downcut bits provide poor chip removal, with no tear-out. A slower feed rate is required when using a downcut bit.
- Compression Cut Bit: Combination of upcut and downcut spirals, great all around bit, great for laminated sheet goods.
¶ Number of Flutes
- Mills have one or more cutting edges.
- Mills with 2 or more cutting edges have cylindrically shape flutes between them to eject chips (similar to gullets on saw blades).
- Typically, the number of cutting edges is equivalent to the number of flutes.
- The more cutting edges, the thicker the core and the smaller the flute size
- Smaller flutes = smaller chips that can be ejected
- In general, the more flutes the finer the surface finish, but less material removed on each pass.
- For wood and softer materials 2-flute mills are sufficient
¶ Before you Begin
¶ Safety Check
¶ Recommended Manufacturers
- Whiteside: whitsiderouterbits.com – made in USA.
- LMT Onsrud: onsrud.com – bits specialized to material being cut.
- Amana tools: amanatool.com – good source for profile bits.
¶ Where to Buy
- Amazon
- Southern Saw
1918 Eastern Avenue
Baltimore, MD
410-327-0050 - Waverly Ace Hardware
601 Homestead Street
Baltimore, MD
443-627-8893
¶ Next Steps
- Install the bit / Toolchange ShopBot
- Install the bit / Toolchange Laguna
¶ Glossary
Bit: The interchangeable cutting tool used in a CNC mill to remove material. There are many different sizes and shapes of bits for different applications. ↩︎
Spindle: The rotating axis at the heart of a CNC router which contains the bit. ↩︎
Chuck: The fitting on a CNC router spindle that holds the collet in place. ↩︎
Collet: The sleeve or collar that holds the bit in place. ↩︎
Shank: The end of the bit grasped by the collet. ↩︎