How To Use A Flush Trim Router Bit When it comes to crafting an electric guitar, certain tools can significantly elevate the quality and efficiency of your work. Among these tools, the router stands out as a game-changer, and one router bit that can make a profound difference is the Flush Trim Router Bit, also known as the Template Copier.

There exist three primary types of flush trim router bits, each serving slightly different purposes and suitability for various occasions. These bits typically consist of a shaft, a straight blade, and ball bearings, with uniform diameters for the bearing and the blade. Their differences lie in the shaft’s diameter, blade length, and the bearing’s position and quantity.

In this article, we will delve into the various variations of these Flush Trim Router Bits, their applications in guitar making, and how to maximize their effectiveness, regardless of your router’s quality. We will also discuss typical routing tasks involved in building a guitar and share some handy tips and tricks.

Applications in Guitar Making: The Flush Trim Router Bit, as its name implies, is designed to cut an edge precisely along an existing line or edge. It is also referred to as the template copier, making it ideal for replicating one or multiple copies of an object or template with a sufficiently straight edge.

In guitar making, particularly when adhering to an existing design, templates are frequently employed for shaping the body, neck, and other components. Using a Flush Trim Bit in conjunction with a template ensures consistent replication of the desired shape, whether it’s the guitar body, neck, headstock, or cavities for pickups, electronics, control knobs, tremolo bridges, and the neck slot.

Anatomy of a Flush Trim Router Bit: A Flush Trim Router Bit consists of three main components: the shaft, the blade, and the bearing.

How To Use A Flush Trim Router Bit
How To Use A Flush Trim Router Bit
  1. The Shaft:
    • Common shaft diameters include ¼”, 3/8″, or 1/2″ for imperial measurements and 6mm, 8mm, and 12mm for metric measurements.
    • Ensure compatibility between your router’s type and the bit’s shaft diameter when making online purchases.
  2. The Blade:
    • Blade diameter determines material removal and the minimum radius achievable in internal corners.
    • Blade length dictates the routing depth, with adjustments possible through the router’s base plate.
    • Multiple passes may be necessary with shorter blades to achieve greater depth.
  3. The Bearing:
    • The bearing ensures that the bit follows the template precisely, facilitating smooth movement along the edge while the blade performs the cutting.
    • Some bits feature double bearings, offering enhanced contact surface, strength, and stability.

Variations of Flush Trim Bits: There are three common variations of Flush Trim Router Bits, each designed for specific routing tasks:

How To Use A Flush Trim Router Bit
How To Use A Flush Trim Router Bit
  1. Bottom Side Bearing Bit (Bearing at the Shaft Side):
    • Versatile and suitable for both table routers and portable router trimmers.
    • Ideal for routing cavities that are inaccessible from the outer side of the guitar.
    • Shorter bits can be used, covering the thickness incrementally.
  2. Top Side Bearing Bit (Bearing at the Tip):
    • Useful for routing in the opposite direction, with the template positioned farther from the router.
    • Requires a long enough blade to encompass the full wood thickness.
    • Not recommended for small trimmer routers due to challenges in use.
  3. Top and Bottom Bearing Bit:
    • Features bearings at both the top and bottom.
    • Allows for easy switching between top and bottom bearing routing by adjusting the bit’s depth.
    • Convenient when altering routing directions without changing bits.

Safety Precautions: Routers are powerful tools that demand caution and care. Always:

How To Use A Flush Trim Router Bit
How To Use A Flush Trim Router Bit
  • Be mindful of the router’s location when turning it on and off.
  • Unplug the router when changing bits.
  • Use protective gear: eye protection, ear protection, and mouth/nose protection to guard against dust and chips.

Routing in Passes: When dealing with hard wood, less powerful routers, or shorter blades, it may be necessary to route in multiple passes. Create a step in the wood by routing partially, remove the template, and align the bearing with the previously routed section for subsequent passes. This technique is useful for gradual depth increases, such as truss rod or pickup cavities.

Routing Direction: Routing direction is critical for safety and maintaining the guitar’s integrity. Always:

How To Use A Flush Trim Router Bit
How To Use A Flush Trim Router Bit
  • Ensure you feel resistance and control as you push the router, preventing it from pulling or jumping.
  • Route with the grain of the wood to prevent chipping.
  • Consider grain direction when planning routing segments, especially for areas with delicate wood.

Quality and Blade Shapes: High-quality router bits and sharp blades are essential for achieving superior results and minimizing accidents. While professional-grade bits can be expensive, they offer better performance and durability.

Do You Need All Types of Flush Trim Bits? The necessity for various types of Flush Trim Router Bits depends on your router and your preferred working method. You will always require a bit with the bearing close to the shaft for routing cavities. Additionally, a “bearing at the tip” bit may be necessary for accommodating grain direction variations. Experimenting with different bit options, sizes, and types can help you find the ideal combination that suits your needs, especially if budget constraints are a concern.

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A Few Router Tips:

  • Familiarize yourself with your router, blade, and wood properties through small tests before working on the guitar.
  • Always initiate the router motion away from the wood and approach slowly.
  • Rout with the grain and be cautious in thinner, more delicate areas, such as the headstock.

Using Flush Trim Router Bits as a Jointer: If you lack a jointer but require a straight, flat edge for gluing or other purposes, use a straight edge as a template. Clamp or tape it with a slight offset from the almost straight edge and run the router with the bearing along the straight edge to achieve a straight profile.

Ultimate Combination for Flush Trim Bits and Routers: In an ideal scenario without budget or space constraints, having a quality table router with a 2″ or larger flush trim blade featuring bearings at both top and bottom would cover most outer edge routing for guitar bodies and necks. Additionally, a medium-sized plunge router with ½” and 1 ½” blades and bearings close to the shaft would be valuable for various tasks.

Other Essential Router Bits for Guitar Building: Aside from Flush Trim Router Bits, several other router bits prove useful in guitar making, including Chamfer or Round-over Bits, Straight Carbide Tip Bits, and Rabbet Bits with multiple bearings. These bits serve various purposes in shaping and finishing guitar components.

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In conclusion, 

Flush Trim Router Bits are invaluable tools in the art of guitar making, allowing for precise replication of templates and shaping various components. Selecting the right type of bit for your router and specific tasks, combined with safety precautions and proper techniques, can significantly enhance the quality and efficiency of your guitar-building projects.