Using a router to create a polished edge on wood is like giving a fresh coat of paint to a dull room. It’s a quick and effortless way to enhance the appearance of plain edges. However, there are certain mistakes that can easily be made if you’re not familiar with woodworking. One of the key aspects to consider when using a router is setting the correct router bit speed. This speed is dependent on various factors such as drill diameter, stock hardness, feed rate, and drill sharpness. While some manufacturers provide suggested bit RPMs on their packaging, this information is not always readily available. To help you with this important task, we have created a convenient router bit speed chart.
Why You Need to Set Your Router Bit Speed
Understanding the importance of router bit speed begins with recognizing the concept of “edge speed.” This can be demonstrated by comparing the performance of milling cutters with different diameters. Whether you’re using a larger plug-in router like the Triton TRA001 or a smaller trim router like the Milwaukee M18 FUEL router, the principle remains the same.
Basic geometry reveals that mills with a 1.5″ diameter and those with a 3.5″ diameter, despite running at the same RPM, have significantly different rim speeds at the edge. In fact, the rim speed difference for the 3.5″ bit is more than twice that of the 1.5″ bit! This discrepancy may not seem alarming at first glance, but it can pose risks to both the wood and the user. The excessive speed can lead to wood burning, amplify drill or router imbalances causing vibration or even dangerous drill failure.
Conversely, running the drill at too slow a speed can result in damaging vibrations that may harm the stock. To help you get started, here is a general guide in the form of a router bit speed chart (maximum speeds; refer to manufacturer recommendations for specific details):
| Diameter | Maximum Speed +/- 10% |
|---|---|
| up to 1 inch | 22,000 |
| 1 to 2 inches | 20,000 |
| 2 to 2.5 inches | 18,000 |
| 2.5 to 3.5 inches | 10,000 |
Typically, the rim speed ranges from 100 to 120 miles per hour. Although you can’t measure it directly, you can use RPM as an indicator of the edge’s miles per hour.
Setting the best router bit speed begins with understanding that the cut is made along the edge.
How Fast is the Router Bit Speed, Really?
To grasp the impact of drill diameter on speed, let’s walk through a few examples. The formula for calculating rim speed involves finding the circumference of the bit, converting it to inches per minute, and then to miles per hour. Let’s calculate the circumferences of some common bit sizes:
- 1 inch diameter drill bit = 3.142 x 1 inch = 3.142 inches
- 2 inch diameter drill bit = 3.142 x 2 inches = 6.28 inches
- 3 inch diameter drill bit = 3.142 x 3 inches = 9.42 inches
Using the following equation, we can now calculate the rim speed at any point along the cutting mill’s outer edge:
Rim Speed = Circumference x Router Speed (RPM)For simplicity, let’s assume a router speed of 20,000 RPM:
- 1 inch diameter milling cutter bit speed = 3.142 inches x 20,000 rpm = 62,830 inches per minute
- 2 inch diameter milling cutter bit speed = 6.28 inches x 20,000 rpm = 125,660 inches per minute
- 3 inch diameter milling bit speed = 9.42 inches x 20,000 rpm = 188,490 inches per minute
Converting these results to miles per hour (mph), we have:
- 1 inch diameter milling cutter rim speed = 59.5 mph
- 2 inch diameter milling cutter rim speed = 119 mph
- 3 inch diameter milling cutter bit rim speed = 178.5 mph
To put it into perspective, a 1 inch mill spinning at 20,000 rpm would cut at approximately 59.5 mph along the edge. On the other hand, the same router would propel a 3-inch drill bit at the cutting edge at a speed of 178.5 mph. Failing to adjust the router speed when switching from a smaller to a larger bit can result in cutting at a significantly higher speed, which can lead to loss of control or worse.
Consider Taking Multiple Passes at the Material
While we encourage you to work within your comfort zone, there are cuts that can be accomplished with ease. It’s important to remember that you don’t have to remove all the material in one go. When creating a round gray table, for instance, we used the router to make multiple passes and gradually cut through material that was over 2 inches thick. Each pass allowed us to go a little deeper, resulting in a clean, straight edge that required minimal sanding.
Using incremental passes to adjust the router bit speed can provide safe and efficient results.
As the drill bit diameter increases or the wood hardens, you can utilize the router for multiple passes. This way, you can maintain a safe and effective rim speed without straining the tool or yourself. Allow the tool to do the work and pay attention to how it feels. If you find yourself exerting excessive force or encountering resistance, it’s time to make adjustments.
Check Your Router Bits for Sharpness
In addition to consulting the router bit speed chart, it is essential to examine the condition of the bits themselves. Only use bits that are in good shape. We strongly recommend wearing safety glasses whenever you’re near high-speed rotating tools—even during routine maintenance. The potential damage from metal flying at 120 mph in any direction can be quite severe. Before operating the router, carefully inspect the bit for any signs of damage. If you detect even the slightest flaw, replace it with a new one. This practice also applies to grinders and grinding wheels. Bits can accumulate sap and wood debris, so make sure to clean them after each use to maintain their sharpness and optimal working condition.
Using Variable Speed Routers vs. Fixed Speed Routers
We do not recommend pairing large diameter drill bits with fixed-speed routers. Fixed-speed routers typically operate at speeds near the upper limit of the RPM range, making them suitable only for smaller diameter bits. Avoid attempting to use larger drills or any aftermarket devices designed to lower the RPM.
Routers are invaluable tools in any workshop. They allow you to transform ordinary lumber into exquisite pieces of furniture in a fraction of the time. To ensure the best possible results, begin by setting the optimal router bit speed.
If you’re a seasoned professional and have additional tips on setting router bit speed, we’d love to hear from you! Share your insights in the comments below or connect with us on Facebook, Twitter, and Instagram.