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If you have had any experience of carpentry or cupboard fitting, you have probably made use of Forstner bits. These drill bits can be relatively expensive, but they will increase the speed and accuracy of your carpentry work. In this article, we examine these bits, how best to use them, how to choose the right one for the job, and finally, we’ll review the best Forstner bits and bit kits.
Why a Forstner Bit?
Invented by Benjamin Forstner in 1874, Forstner bits form an essential part of any carpenter’s toolkit. They are used for precision-drilling wide, smooth-sided holes with a flat base.
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.
Designed for a Drill Press
Forstner drill bits are best used in a drill press where constant pressure can be applied to a stable surface. It is possible to use a hand-held drill for the task but the bit has a tendency to walk when used in this way, and the result is a messy hole.
Force is required for a high-quality precision hole. The bigger the bit, the more difficult it becomes to control in a hand-held drill. It is also difficult to effectively regulate the speed of a handheld drill, reducing the cutting life of the bit.
The best Forstner bits can be used on most woods and wood composites. They are accurate at any angle and do not follow the grain of the wood because the outside perimeter of the bit guides it. These bits are commonly used for cutting the holes for concealed hinges on cupboard doors Forstner bits are useful for:
- Drilling flat-bottomed holes.
- Drilling pocket holes
- Enlarging existing holes
- Drilling overlapping holes, great for mortise joints. Drill the flesh out of the center of the mortise and then use a chisel to clean it. It’s quick and easy.
- Drilling holes that are at an angle to the surface of the material.
Before buying a Forstner bit, several features require your consideration.
- The size that you require will depend on the job at hand. While some people will buy parts individually for various jobs, this can be pricey, and it may be a better idea to purchase a full kit. The bits come in a variety of sizes all the way up to four inches, and they are available in both imperial and metric sizes. If a deep hole is required, you may need a Forstner bit extender.
- Material – Most bits will come in one of two high-grade steel materials
- High-Speed Steel -this is the cheaper of the two acceptable materials and will stand up to rougher treatment than tool steel. This material can manage high temperatures
- Carbide based steels are a lot more expensive but will hold their sharpness for a longer time. Use tungsten carbide tipped bits for plywood, hardwood, chipboard, wood fiberboard, plastic laminated wood, and other abrasive materials.
- Edges – The most significant differences that you will encounter between Forstner bits are on the outer perimeter. The edge determines the accuracy and the repeatability of the hole size and dimension. There are three major rim designs available. They are sawtooth rims, knife edge or continuous rims and wavy rims
- The sawtooth rim creates less friction and therefore less heat so they can run at faster speeds, but the sawtooth sometimes skips, and the edge may not be as clean as can be achieved with the other bits. This rim is also not the best choice for boring at an angle, or when overlapping holes are cut as it can produce a rougher cut.
- The continuous rim is solid and knifelike. It makes much cleaner, more accurate holes but can build up a fair amount of heat, so unless you pay attention to the speed with which you run these bits, you could end up blunting them quickly.
- The wavy rim is a pretty good attempt at a compromise between the sawtooth and the knife edge rim and is now used on many Forstner bits.
When they are new, all three cutting edges will do an excellent job of cutting a clean hole.
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.
Sharpening the Bits
Forstner bits, particularly the large ones, can be expensive, and even with the best of care, they will get blunt with use. Blunt bits will not feed properly, and the chips are likely to become jammed.
Sharpen the bits by running a flat diamond file along the horizontal cutter at a steady angle. The rim should stay sharp for longer, but you can sharpen this by running a diamond stone or round file along the inside of the rim. You should never file the outer rim of the drill bit.
Our Picks for the Top 5 Forstner Bits and Bit Sets – Reviewed
1. PORTER-CABLE PC1014 Forstner Bit Set
This large fourteen-piece Forstner bit set includes frequently used sizes from one-quarter inch to two-inch bits. The bits are packed in a decent storage case with snug slots for each.
Although not made from top quality materials, at its price-point, this kit is fairly good value for money. The bits are manufactured from hardened steel to ensure durability, but you may find that you have to sharpen them frequently. The open tooth design, which creates less heat, means that you can make clean holes quickly.
This has historically been a popular product, as the home carpenter gets a full set of bits at a relatively low price. Professional carpenters may, on the other hand, prefer to purchase a more expensive set. The product comes with a thirty-day money back guarantee.
2. FORSTNER DRILL BIT SET, 7 PCS, White & Tin Coated Finish
This seven-piece metric Forstner kit includes drill bits that range from six to twenty-five millimeters. They come in a well-made and snug fitting box. This ensures that the kit is kept organized, and the drill bits are well protected and easy to transport. The box is nicely labeled so that bits go back into the same space every time.
Impressively, the bits in this inexpensive kit are made from high-quality materials. They are solidly built and quite capable of drilling a clean and precise hole.
All in all, this kit is good value for money. The bits are compatible with a large number of drills.
3. Freud FB-003 1/2-Inch by 5/16-Inch Shank Forstner Drill Bit
Freud is known for using high-quality steel in the manufacture of Forstner drill bits. This half inch bit is precision machined. The rim has a wavy edge that allows for quick, clean cuts without overheating the bit.
The bits have a fast cutting design and reportedly easy to line up. They are made to cut clean, smooth holes without skating or tearing, precision cutting hardwoods. It leaves the bottom of the hole smooth, generally with little need for cleaning or sanding.
The well-balanced drill bits offer relatively high precision. Because they are made from high-quality steel, these bits are sharp, and they tend to stay that way for a good time. They also do a great job of evacuating wood curls, meaning that they don’t clog up.
Freud stands by their product offering a limited lifetime warranty on the drill bit.
4. MLCS 9245H 3-Inch Diameter Steel Forstner Bit with Hex Shank
This reasonably priced Forstner bit has a hex shank, which helps to reduce slippage in the chuck. It is made from high-quality steel designed for heavy use. The bits, available in sizes that range from one-quarter of an inch to seven-eighths of an inch have solid rims. Larger bore sizes, such as this three-inch bit have sawtooth rims.
Although inexpensive, the cutting edge of this drill bit has some important problems. Users report that t is not sharp enough and even when sharpened, was soon blunt. Also, the bottom cutting blades are reportedly not smooth enough and sometimes leave concentric rings on the bottom of the cut hole.
This product will serve you well if you require it for occasional use. If you plan to use the product regularly, you would be well advised to buy a more expensive bit.
5. Forstner Drill Bit, Ankoow 6Pcs 16mm-35mm
Another inexpensive Forstner bit kit, but this one is less a kit than six individual pieces since it comes without a case or bag. The six-piece set includes 16mm, 20mm, 22mm, 25mm, 30mm, and 35mm Forstner bits. The alloy blade, made from hardened and tempered carbon steel is durable, as are the shafts, which are made from anti-corrosive materials.
The bits reportedly cut good, clean and precise holes with no burrs, and we consider this product to be excellent value for money.
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.