Forstner bit vs Spade bit

Hole drilling is common in woodworking, but the required tools, forstner bits and spade bits, are designed for fundamentally different jobs. While both create large-diameter holes, they offer an essential trade-off: the spade bit prioritizes speed and utility, and the Forstner bit prioritizes cleanliness and precision.

Forstner Bit vs. Spade Bit: Design and Mechanism

The core difference lies in how each bit engages the wood.

What is a Spade Bit?

Spade bits (or paddle bits) are flat in shape with two sharp tips (cutting lips) and a pointed middle pilot. They are designed for rough utility work where speed is paramount. Their design causes aggressive cutting action with less surface friction, but they tend to produce rougher edges and often cause blowout (splintering) when they exit the wood.

What is a Forstner Bit?

Forstner bits feature a split-ring design: the outer rim (spur) shears the wood fibers cleanly before the inner blade removes the bulk of the material. This two-stage action is why they produce holes with immaculate edges and a perfectly flat bottom, making them ideal for high-end visible work.

Forstner Bit vs. Spade Bit: Performance and Application

The difference in design dictates how fast and how accurately you can work.

1. Application: Precision vs. Utility

Forstner bits are ideal for decorative drilling work and high-precision applications, particularly in hardwoods, where a clean edge is essential. Their core job is drilling the large, precise flat-bottom cups required for mounting modern European-style cabinet hinges (e.g., a $35 \text{mm}$ hole).

Spade bits are recommended for utility installation projects, such as drilling holes through studs or walls for electrical wires or plumbing runs, where the hole will be hidden, and speed is the only concern.

2. Cutting Speed: Spade Bits are Faster

Spade bits cut with less friction and contact area, allowing them to be run at a faster RPM, thus removing wood quickly.

However, the Forstner bit's full-circle design creates a larger contact surface, generating more friction and heat. To prevent dulling the bit or burning the wood, Forstner bits (especially larger diameters) must be run at a slower RPM than spade bits.

3. Angled and Partial Drilling

Forstner bits do a superior job of drilling at an angle or on the very edge of a workpiece. The outer rim bites into the wood first, preventing shifting or "walking." This rim also allows the bit to cut partial holes or overlapping holes, which is impossible with a spade bit due to its large, necessary central pilot point.

4. Maximizing Precision with a Drill Press

While both can be used with a hand drill, the Forstner bit's precision is highly dependent on vertical stability. Using it in a drill press allows the operator to:

• Apply consistent, straight downward pressure.

• Set the correct slower RPM required for clean cutting.

• Limit the drilling depth precisely, guaranteeing the clean, flat bottom and preventing blowout on the back side.

5. Size and Cost

Spade bits are generally available in smaller sizes (up to about 36 mm or 1-1/2inches) and are the cheaper option, as they require less material and complex machining to manufacture. Forstner bits are available in a far wider range of large diameters, often up to 90 mm or 3-1/2 inches. If your work requires large, clean holes, the Forstner bit is the necessary, though more costly, preference.