A brief guide to CNC router drill bits

January 28, 2020

Hooray! You’ve just bought a new CNC router. But, before you slap on some scrap material laying around in your shop or garage, there is a few things you need to know to get the most out of your CNC router bits.

CNC router terminology 

To get started, we compiled a list of routing jargon and their respective definitions which is listed below.

  • Chipload: The physical size of the pieces or chips the bit cuts off the material.
  • Feed Rates: How quickly a machine can laterally move through the material being cut. Typically measured in Inches Per Minute (IPM).
  • Speed Rates: The speed of the machines spindle. Typically measured in Revolutions Per Minute (RPM).
  • Flute: The number of cutting edges on a routing bit.
  • Toolpath: A coded route which a machine follows as a guide in order to cut.

Types of cuts

It’s safe to say, specific bits are designed to work best with specific materials. Once you’ve figured out what materials you will be cutting the next step would be determining your cut direction.

  • Up cut: Most regularly used type of cut. Sends chips up and out of the way of the cutpath.
  • Down cut: Used for specific applications such as laminated or thin material. Pushes chips down in spoilboard.
  • Compression cut: Combines Up andDown cuts. Reduces chipping which leaves a smooth finish on top and bottom of material.

For most plastic and aluminum applications, a single flute pattern is preferred, while for most wood applications it is ideal to utilize a double flute pattern.

When it comes to selecting routing bits, remember the thicker the routing bit, typically the deeper the pass. Although, be conscious of the bit diameter in order to not unnecessarily waste material. It is also best practice to match the size of your bit to the size of the material you’re cutting. For example a ¼ inch sheet of plastic would ideally be cut with a ¼ inch bit.

Prior to cutting

Before you start cutting away at lighting fast speeds, there are a few factors you need to consider. First, determine what type of material you will cut, the thickness of it, and the type of application (cutting, engraving, pocketing, etc.) in order to set an outcome. Secondly, establish if you want to the toolpath to be a single pass or have multiple passes. Lastly, prior to running a cut file, follow the manufactures recommendations for a routing bits recommended chipload. These recommended specs can usually be found on their website, documentation, or manual. The formula provided below will assist you to calculate your chipload.

Chipload = Feedrate / (RPM x Number of Flutes)

General rule of thumb: If your chips are too large, slow down the feed rate or you risk breaking the bit.

Larger chips dissipate heat better while smaller chips are easier on your machine but can result in too much heat. Also, consider the speed you are looking to cut and the chip clearance. The model RPM for nearly every material is around 18,000 RPM but for aluminum it’s suggested to aim for around 16,000 RPM.

Have more questions about which CNC routing bits are best for your application or material? Feel free to leave your comments or questions in the section below or contact our Aftermarket Specialist, Nathan Roberts at (972) 929-4070 ext. 2027 – email at Nathan@multicam.com. Be sure to connect with us on our social media pages via, Facebook, LinkedIn, and Twitter for our latest company updates.

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