Technical Tip of the Week: The difference between Upcut and Downcut CNC router bits

Tool selection is critical when it comes to achieving a desired surface finish, tool life, or cut speed of a specific material. Tooling manufacturers go to great lengths to engineer tools to deal with specific aspects and properties of certain materials. Selecting the right tool for the job could determine whether a job fails or succeeds.

In this scenario, we are discussing the different between upcut and downcut CNC router bits.

What is an upcut router bit?

Upcut spiral tools are the most popular type of spiral fluted tool. Use these for grooving or slotting, for upward chip evacuation and best finish on the bottom side of the part.  These bits allow for rapid cuts since the tool clears the chips away from the material.  While ideal for cutting thicker materials, this type of tool is not recommended for thinner or softer materials. When working with these types of material, the upward force can pull the material causing a ragged finish on the top surface, or even worse, eject the part from the table. This type of geometry is used whenever the best finish is needed on the bottom side of a part.

What is a downcut router bit?

Downcut spiral tools are best used for thinner materials which will be pushed down into the machine bed rather than being lifted with an upcut spiral. This can be particularly useful when using vacuum hold down where maintaining the seal between the material and sacrificial bed is crucial. These tools are predominantly used when a high quality cut finish is required on the top surface of cut parts.

Downward spiral tools often require reduced cutting speeds because the chips are pushed back into the material. The chip extraction is generally less effective with this type of tool than it is with an upcut spiral tool.

When is it recommended to use a downcut router bit?

Downcut spiral tools should be used when processing thin materials, 1/8” (3.175mm) or thinner.

At AXYZ, we hold a vast range of downcut CNC router bits from industry leading tooling manufacturers such as LMT-Belin and LMT Onsrud. These bits range from 1/16” to ½” cut diameters and can be found at CNCshop.

You can purchase general purpose downcut bits or dedicated tooling for wood, plastics, aluminum, and other non-ferrous metals. You can find them all at our one-stop shop.

Author: Andrew Centofanti is a Technical Sales Representative for AXYZ, a global manufacturer of CNC router and knife systems. Andrew’s in-depth knowledge about AXYZ’s tooling, parts and accessories line will help you get the most out of your machine and understand how to use it safely.