Flush Trim Router Bit: How to Choose & How to Use It

A flush trim router bit is one of the common router bits used in woodworking. As its name suggests, it trims the edges of a workpiece to make it flat and flush (even) with a template. It consists of a cutter, a shank, and one (or two) bearings. The bearings are in contact with the surface of the template to help maintain a consistent edge trim.

This bit is usually used for edge trimming, template routing, laminate trimming, and joinery. It is versatile and provides accurate and precise cuts for woodworking production. It can produce smooth and clean edges, reducing the need for additional sanding or finishing work. Moreover, it reduces material waste, making it a cost-effective tool.

Understanding the flush trim router bit can provide an efficient edge trimming experience. This post will give you a comprehensive overview of the trim router bit, exploring its types, uses, and considerations for choosing one.

Types of Flush Trim Router Bit

A flush trim bit uses bearing guides to route to a precise pattern. Bearings prevent the cutter from exceeding a certain depth of cut and are easy to replace when badly worn. As a bearing-guided router bit, it has three types of bearing placement: top bearing, bottom bearing, and double bearing.

• Top/bottom bearing: When using a flush trim bit with a single bearing, place the template and the workpiece according to the router in your workshop.
• Double bearing: The bearings are at the top and bottom of the cutting edge. It provides excellent guidance and smooth surfaces, whether the template is above or below the material.

In case of uniform bearing position, flush trim router bits are further classified into straight and spiral. The following content is an introduction to them. To know their differences, refer to Spiral Router Bit vs Straight Router Bit: Which One is Better.

Straight Flush Trim Router Bit

Straight flute: It might be subjected to high instantaneous resistance during processing. The trimming effect is greatly reduced when its edge is worn out. However, its low cost makes it the preferred choice for many woodworking beginners and those with only simple machining needs.

Angled flute: Compared with a straight flute, it has greater shear force, which can reduce material tearing and the instantaneous resistance of the cutting edge to some extent. It also makes less noise and puts less load on the equipment. But its cost is a little higher.

Spiral Flush Trim Router Bit

There are three classifications of spiral router bits: up-cut, down-cut, and compression. In this section, we will give you a brief description of them.

• Up-cut: It pulls wood chips up and reduces chips on the lowermost surface.
• Down-cut: It pushes chips downward and minimizes the chips on the uppermost surface.
• Compression: The compression spiral bit combines up-cut and down-cut on the same bit.

In addition to the common flush trim router bits mentioned above, there’s a type of bit that comes with carbide inserts. The flush trim router bit with carbide inserts reduces the resistance of the cutter by dividing the whole cutting edge into several sections. Moreover, this unique design allows the bit to be reused by simply replacing the damaged inserts in the event of chipping due to cutting into impurities.

How to Choose a Flush Trim Router Bit

After knowing different types of flush trim router bits, it's time to choose one for your woodworking task. You might be confused when faced with hundreds of options. How do you choose? Here are some considerations for selecting a flush trim router bit. Follow us and pick one.

Size & Shape of the Router Bit

• Diameter: The diameter of a flush trim bit determines the maximum width it can trim. If wider edges need to be trimmed, the one with a larger diameter is more efficient.
• Length of cutting edge: The cutting length influences the trimming depth and the working area. You should consider the thickness of the workpiece to be processed.
• Length of shank: The shanks come in two common sizes: 1/4’’ and 1/2’’. Except for very small and very large profiles, both shank lengths are available.
• Shape: As mentioned above, it has different cutting edges. Generally speaking, the compression spiral flush trim router bits and those with carbide inserts cut smoother and reduce vibration.

Placement of Bearings

There are three bearing placements: top bearing, bottom bearing, and double bearing. Choose the appropriate one according to your requirement and the router you have (handheld or router table). We recommend the double bearing the most.

Desired Outcomes

• Precision: If you require high-level precision and accuracy, select a bit that cuts smoother and with less vibration. For example, a spiral flush trim bit performs better.
• Time efficiency: Choosing a more efficient bit is essential, especially when handling large-scale trimming work. A flush trim router bit with a large diameter can increase the trimming speed.

How to Use a Flush Trim Router Bit

1. Refer to the instructions above to select a suitable flush trim router bit.

2. Prepare the workpiece and install the flush trim bit.

• If you are using a handheld router, make sure to clamp the workpiece securely. Clean up any debris or obstructions that may interfere with the router. Then, adjust the router base to your desired depth.
• If you are using a router table, insert the flush trim router bit into the router collet and tighten it securely with screws. Next, adjust the depth of the bit so that the bearing can move along the edge of the template.

3. Place and secure the template with the workpiece. Allow the bearing to move along the edge of the template to guide the router.

4. Move the router slowly and steadily to ensure a smooth, flat surface.

5. After routing, check the edges for roughness or tear-out. Sand and finish the edges according to your desired achievement.

Bonus Tip: Safety Precautions

1. Wear personal protective equipment such as goggles and earplugs to prevent splashes of wood chips and splinters from hurting your eyes, and to reduce noise damage to your ears.
2. Be sure to tighten the screws and secure the flush trim router bit tightly.
3. When cutting, always observe whether the bearing rolls smoothly. If you feel significant resistance, power off the router immediately and check the bit.
4. Set an appropriate rotating speed. Generally speaking, a speed of 8000-18000 rpm
   is reasonable for flush trim bits. You can adjust the speed according to the actual situation.
5. Clean up the residual chips, glue, and other debris on the cutter, which might influence the performance of use.
6. Maintain the bit regularly. Replace the bit in time when the cutter becomes dull and worn to ensure cutting quality and efficiency.

Bottom Line

After reading this article, you should have a general understanding of the flush trim router bit. Overall, a double-bearing spiral flush trim bit with carbide inserts is the best choice.

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It’s worth mentioning that there is a 5% discount for newcomers.

FAQ About Flush Trim Router Bit

#1. What is a flush trim router bit for?

This bit is usually used for edge trimming, template routing, laminate trimming, and joinery.

#2. What is the difference between a straight bit and a flush trim router bit?

A flush trim router bit is a type of straight bit, but it has bearings, while some of the straight bits do not. Bearings prevent the cutting edge from exceeding a certain depth of cut and are easy to replace when badly worn.