When it comes to drilling large diameter holes, spade bits and Forstner bits are two of the best options available. This doesn’t mean they’re interchangeable though, as each one has its respective strengths, weaknesses, and ideal use cases.
If you’re unsure about when to use a Forstner bit vs a spade bit, don’t worry. I’ll break down each type of drill bit in detail, so you’ll have a solid grasp on when to reach for each one.
|Forstner Bit||Spade Bit|
|Common Use||Drilling precise holes for woodworking.||Quickly drilling rough holes in wood.|
|Size||1/4 inch to 3 inch||1/4 inch to 1-1/2 inch|
|Material||Hardwoods and softwoods||Wood and some plastics|
Spade bits – also called paddle bits – are flat bits used primarily for quickly drilling holes through wood, plywood, and some plastics. They’re designed to quickly punch holes in a material and tend to sacrifice precision in favor of speed.
Spade bits holes can be a little rough looking, so they tend to be used mostly for rough construction rather than fine finish work. Think of an electrician or plumber drilling holes through wall studs to run electric cables or plumbing.
Spade bits have a tendency to create tear out on the opposite end. So if you’re after a clean-looking hole you’ll need to use a piece of scrap wood for backing or remove the bit halfway and drill from the opposite end.
Spade bits are typically used for drilling holes between 1/4-inch and 1 1/2-inches, any larger than that and you’ll need to reach for a Forstner bit or a hole saw.
There are a number of variations when it comes to spade bits, with differences in cutting edge shapes as well as different tip designs. Threaded auger tips are a common variation, sporting an aggressive tip that increases the grips the material and increases speed.
Forstner bits are specialized drill bits designed to drill clean flat bottomed holes with a high level of precision. They’re typically used for drilling in wood and can handle hardwoods just as well as softwoods.
Unlike spade bits, they are intended to bore accurate holes with minimal tear out or defects and sacrifice some speed to accomplish this.
They are the only type of bit that bore a clean flat bottomed hole, which makes them a highly versatile fine woodworking tool. And because they’re rim-guided rather than center point guided, you can use them to drill all sorts of partial, overlapping, and even angled holes.
Forstner bits are commonly used in a drill press to bore highly accurate holes with precise tolerances.
Due to their tendency to slip or ‘walk’ on the work surface, there is a common misconception that they can’t be used in a handheld drill. This is an inaccuracy – they can be used with portable drills as long as you take a few basic precautions.
Forstner Bit vs Spade Bit Comparison
Now that you’ve got a basic understanding of Forstner bits vs spade bits, let’s take a closer look at some of the differences between them.
Spade bits are typically used when you need to quickly bore a hole through wood and you don’t particularly care how nice it looks when finished. This makes spade bits a favorite of contractors, tradesmen, and anyone who needs to get the job done in a hurry.
Spade bits tend to leave somewhat rough holes and can tear out and splinter on the opposite end of the workpiece. This is not much of an issue if you’re punching holes in wall studs, but can present a problem if you try to use one to make a clean hole for a woodworking project.
Forster bits bore significantly more refined holes than spade bits, which makes them ideal for precise woodworking tasks like dowelling, drilling pocket holes, removing material from a mortise and tenon joint, and making clean counterbored holes.
They’re also the only drill bit that leaves a clean flat bottom, so they work well for drilling partial holes in wood. When used in conjunction with a drill press, Forstner bits can bore perfectly plumb flat bottomed holes with no imperfections.
Another major difference between the two bits is their speeds. Simply put, spade bits are fast and dirty, while Forstner bits are slow and precise.
In fact, if you’re not careful when using a spade bit, the speed can cause tear out and splintering on the opposite side of the workpiece. Forstner bits don’t have this issue, and their slower pace tends to produce clean holes on both sides.
Both Forstner bits and spade bits are designed to drill holes in wood. Spade bits tend to work best in softwoods, while Forstner bits can be used in both hardwoods and softwoods.
People sometimes ask if spade bits can be used to cut holes in metal – the answer is essentially no – especially not if you planning to use the same bit again. The ideal bit for cutting holes in metal is a bi-metal hole saw.
Another area where these two bits differ is the available sizes.
Spade bits generally come in sizes between 1/4-inch and 1 1/2-inch. Forstner bits are generally available in sizes between 1/4-inch and 3 inches, with the larger sizes being less common.
In addition to the bit diameter, there is also the depth to consider. Spade bits typically have much longer shanks than Forstner bits, making them better suited for drilling deep holes.
Foster bits typically feature short shanks between 1 and 2 inches long, although you can use a bit extension if you need to add additional drilling depth.
Spade bits tend to be very inexpensive, with a decent set of a dozen spade bits available for less than $20. This makes them a good option for rough construction as if a bit breaks it can be easily replaced for minimal cost.
Forstner bits are significantly more expensive than spade bits, with a decent set costing $50 or more. This makes them a more expensive option for drilling holes in wood.
Spade bits are ideal for rough construction work with softwood, while Forstner bits are geared towards precision woodworking with hardwoods or softwoods.
Due to their precise nature, many people tend to use Forstner bits in a drill press for added precision. These bits are unique in their ability to bore clean flat bottomed holes in wood, making them the ideal choice for drilling partial holes, overlapping holes, and even angled holes.