Forstner Bit vs. Spade Bit – What’s the Difference?
Hole drilling is very common in woodworking, but there are different types of drilling bits that you can use for the job. Among these, Forstner and spade bits are very popular, but they have different designs and different cutting methods.
Forstner bits are circular and have a split ring design with a cutting blade forming the ring, a flat blade across the diameter, and a pointy tip in the middle for guidance.
On the other hand, a spade bit looks like a spade because it is flat with two sharp lips for cutting and a middle pointy tip for guidance. All the differences include:
Forstner bits are recommended for drilling holes in hardwood because they are tougher and have a wide cutting surface area as compared to spade bit. They are also ideal for decorative drilling work.
On the other hand, spade bits are recommended for utility installation projects such as drilling holes through walls for electrical wires or plumbing. Also, if you want to drill multiple holes in a short time, this is the best one to use.
2. Clean Cutting: Forstner Bits Produce the Cleanest Cuts
The reason Forstner bits are ideal for decorative drilling work is that they produce very clean cuts. This can be attributed to the blades around the ring, which ensure the edge of the drilled hole is kept neat, with very few chippings and no blowouts.
These ring blades also work in tandem with the inner flat blade that runs across the diameter to produce flat-bottomed holes that are very neat.
However, with spade bits, they only have a flat blade with two cutting lips on the sides. This produces rougher edges and is therefore ideal for drilling in hidden surfaces such as inside walls for installations where the drilling quality is not a big issue.
3. Cutting Speed: Spade Bits Are Faster
While the design of the Forstner bit gives a cleaner cut, it drags the spinning and cutting speed down because there is a larger surface area contacting the wood.
Additionally, this extended contact surface creates more heat, and therefore, attempting quick cuts by spinning the drill faster might dull the bit or cause permanent damage.
On the flip side, with a reduced cutting surface area, spade bits chop off the wood with less friction and generate less heat in the process. As such, they cut at a faster rate as compared to Forstner bits.
4. Angled Drilling: Forstner Bits Do a Better Job
Even though the center pointy tip is the one meant to guide the bit into the wood, the outer rim of a Forstner bit plays a big role in this guidance, especially when drilling at an angle.
The blade at the rim bites into the wood at the start of the cut and this prevents shifting or skipping, which might affect the quality of the edge of the hole.
With a spade bit, you only get a middle pointy tip as a guide, and therefore, you need to apply some strength to hold it in position, be it when drilling straight or at an angle.
5. Precision Vs. Modifiable Drilling
With its circular design, a Forstner bit is ideal for precision drilling. Its outer rim blade allows for precision cutting at the exact point you want the hole and creates a clean flat-bottom. This also prevents shifting as you begin the cut.
With a spade bit, however, you can modify the shape of the hole by tilting its sides. This gives you some customization options because it is possible to carve out a tapered hole or drill a hole that is smaller than the size of the bit.
Each of the bits is uniquely different and therefore, selection should be based on the shape and type of cut you want to make.
6. Size: Forstner Bits Give You More Size Options
Spade bits are usually available in small sizes and with fewer options to choose from. These range from 6mm to 36mm, which is the length of the flat blade (diameter of the hole).
Forstner bits come in a wide variety of sizes and these are usually large diameter bits. They can range anywhere from 10mm to 90mm and this makes them suitable for drilling large holes.
Lastly, if you are on a tight budget, a spade bit is the better option to buy because it is more affordable. This can be attributed to the fact that less material is used to build it (no outer rim).
However, if you can afford it, a Forstner bit is the best choice because it cuts better, provided that it matches your usage requirements.
After reading through, you should have realized that apart from looks, the main difference between the two bits is precision and this brings about the aspects of clean cutting and speed.
That said, each type has its unique applications and this should be the primary factor when determining which one to buy.