Forstner Drill Bit Buying Guide
All Forstner bits have a centering pin for accurate location. They have a cutting edge or rim that makes a clean cut on the sides of the hole, and a scraping edge that ensures the bottom of the hole is smooth. They have radial cutting edges which allow them to clean the wood off the bottom of the hole, working like a rotary plane.
While spade bits and hole saws can be used for making holes in wood, the Forstner bit provides the cleanest finish. These bits can be used to drill holes that partially overlap or holes on the edge of the wood that other bits cannot manage. They are rim rather than center driven. Consequently, you can use them drill partial holes without any drag caused by the wood grain.
How to Use
With all their good features, we don't use them for every job because they're a little bit fragile, compared to other drill bits. Excessive speed, or too much force without a break, can ruin the bits in seconds. The larger the Forstner bit, the faster it can be ruined by excessive speed. What happens is simple: because of the bulk of the bit's body, it heats up rapidly, so that you must keep speeds down (compared to possible speeds with HSS standard drill bits and even those allowable with brad point bits). If the bit body heats up enough, the heat draws the temper from the bit. A blued Forstner bit is ruined.
That said, high speed steel (HSS) Forstner bits don't lose temper easily, and carbide tipped Forstner bits are even sturdier. Both, though, work far more efficiently within clean holes, so the clean-out requirement remains.
The first job, then, is to limit the speed of the drill you're using, whether a hand drill or a drill press. If you're using a trigger controlled hand drill, set it on the lowest possible speed range, and then pay strong attention to the actual speed of the drill chuck.
Hand drills can't be as tightly speed regulated as can drill presses, so constant attention to their speed is essential: in fact, though, it's really best not to run Forstner bits in handheld drills, because of the lack of speed control (and accuracy--Forstner bits are made for clean, neat, accurate holes, which is seldom what a handheld drill produces, regardless of bit type). The list below shows the safe running speeds of different sized Forstner bits, with the smaller sizes able to run at pretty much the same speeds as twist drills, while the larger sizes--at the top of the lists--must move more slowly.
An important step in the interest of keeping your Forstner bits sharp and in good shape is cleaning the hole bore often. Forstner bits do not have flutes that can pass chips up and out to the surface of the piece being drilled, so it's necessary to lift the bit out of the bore, or almost out of the bore, every 15 to 30 seconds.
Caring for your Forstner Drill Bits
Good drill bits are expensive, but when treated with care they can last for years. They are best stored in a case where they cannot roll around, preventing damage to the cutting edges.
Each time you use the bits, clean them with a wire brush and some three in one dry lube to maintain their sharpness.
In use, Forstner drill bits tend to heat up, which leads to blunting. To maintain the strength and sharpness of the bit, use lower speeds. The larger the bit, the more easily it will be damaged by high speed. Ensure that the borehole is cleaned out every fifteen to twenty seconds to prevent clogging which will also cause blunting.
With increased competition between manufacturers to produce the bit with the sharpest cut and the smoothest edge, a number of materials have been incorporated in Forstner bit metals to improve qualities such as durability and resistance to rust.
Steel still ranks as the commonest and most used metal. Beside it are a few other materials. In any tool shop, you will be presented with Forstner bits made of either stainless steel, plain steel, titanium coated steel or carbide.
Depending on your knowledge of each material's functionality, you might not have trouble making your pick. If not, a few tips should get you up and going.
The first is that steel models are known to start out with sharper edges than carbide models, while carbide models end up having a longer edge life than any variation of steel.
Forstner vs. Hole Saw
Hole saws are generally much faster, if you’re running conduit through a 2x4 in framing or something they’re probably the better choice. They’re also easier to use with a hand held drill since they don’t need such a low speed.
On the other hand Forstner bits deliver a clean hole with a greatly reduced chance of tear out or other “mess” that a hole saw leaves behind. They’re worth the price for any kind of specialized holes you need.
What are Forstner bits used for?
Forstner bits are mainly used in woodworking to create holes that are larger than holes that standard drill bits can make. While there are other types of drill bits – like spade bits – that can do a similar job, Forstner bits are much more precise and create a clean cut with a flat bottom.
Can I use the Forstner drill bit on metal?
While these bits are primarily designed for woodwork, you can certainly use them on soft metals.
Do the Forstner drill bit give nice cuts?
Forstner drill bits are quite precise in cutting; you get straight edges and neat cuts.
Forstner bits are a necessary part of any wood worker’s toolkit. Chosen wisely, and properly cared for they make life easier, can last for years and could help you to make well finished and professional woodwork designs. Avid carpenters could save time and money by choosing the best Forstner bit kit.