The Forstner drill appeared in 1874 when engineer Benjamin Forstner patented his invention for drilling wood. Since the creation of the drill, many modifications to this tool have been made. New Forstner drill samples have a different structure, but retained its principle of operation. This tool is used in those areas where you need to make a smooth and accurate hole, while the workpieces can be not only made of wood - it can be drywall, furniture plate, polymeric materials.
The modification of the drill depends on what raw materials to work with, as well as on the task to be performed. Drills have different quality, on which their cost directly depends.
What is it and what is it used for?
Forstner drill - a kind of cutter that works most often on wood. In the process, 3 cutting edges are involved in the tool - a circular rim cuts the edge of the hole exactly according to the specified diameter , the central pointed protrusion helps to set the cutting process in the right direction, and two paired cutting surfaces, like small joiners, cut the plane of the material layer by layer. The result is a flat hole with a flat bottom or a through hole.
The tool is widely used in wood processing of soft and hard wood. Its purpose is to make through or blind holes that are needed to install locks, for hinges, for couplers of a threaded or eccentric type, for holes needed when installing accessories. In the processing of modern types of materials, the Forstner drill has proven itself when working with MDF, chipboard, DPV boards and their various options.
As a result of processing the edges of the hole are clean, without nicks and rough roughness.
In addition to woodworking, the Forstner mill can be applicable for installation work on installing window frames , when conducting channels for electrical wires, when installing plumbing equipment, plumbing and sewage systems. Forstner drills are installed in the chuck of an electric drill or screwdriver and operate at 500-1400 rpm. The speed of rotation of the drill depends on the diameter - the thicker the drill, the lower its rotation speed should be.
For the manufacture of drill used high-strength steel, which has high-speed properties. In the process, thermal energy is generated, and such steel withstands it well, while retaining its properties. To make an even more durable tool, manufacturers cover their products with a thin layer of titanium or apply hard alloy soldering to the working area. To increase the efficiency, the cutting edges of the drill can be with notches that better capture the material, but at the same time the purity of the cut processing is lost. Based on the quality of the alloy that was used in the manufacture of the drill, its cost also depends.
Advantages and disadvantages
A tool for drilling holes has a lot of positive properties, but, like everyone else, it is not without some negative characteristics.
Advantages of the Forstner drill:
- well sharpened sharp edges of the drill are the indisputable guarantee of high-quality and smooth processing of the workpiece material;
- the tool can be used with a manual electric device or mounted on a stationary industrial type machine;
- the direction of the cutting elements in the hole of the material occurs not only due to the sharp centered protrusion, but also with the help of an edge in the form of a closed ring, as well as the entire cylindrical working part of the drill;
- even if the diameter of the hole during operation extends beyond the workpiece, the specified direction at the drill does not change, performing high-quality and smooth cuts without the formation of chips and burrs on that part of the product where possible.
The smoothness of the cut when processing the workpiece with a milling cutter occurs by cutting the wood fibers around the circumference. Moreover, this process occurs even before the moment when the main working edge of the drill begins to touch these fibers.
This drill has its drawbacks:
- the cutting parts of the cutter are at some distance from each other, which does not give them full contact with the working surface as it happens with the edge of the annular rim, as a result of which the drilling process is accompanied by vibration of the tool, and there is a risk that the cutter may simply jump off the intended holes;
- if the cutting blades are equipped with teeth, then the vibration increases during operation, and the risk of the drill popping off the intended stencil increases;
- Forstner drill costs more than other similar tools designed for drilling holes.
Despite some disadvantages, the drill has a high level of productivity and a long term of use, subject to the rules of application.
Various versions of the Forstner drill are produced today by both domestic and European manufacturers - a wide range of their products is presented on the Russian market. Many companies are trying to improve the design of the drill for the convenience of its use, therefore, on sale you can find models with a limiter for drilling depth, which can be either fixed or adjustable. In addition, models that can be machine-sharpened are very popular. For such a drill, the cutting edge of the rim on the back of the cutters has a special cut.
Forstner drill cutters are also modified, depending on their type, the models are divided into two main groups.
With carbide cutters
The design feature of such a tool is that some modifications have cutters to which sharpened elements are soldered, made of alloys of carbon-containing steel of increased hardness. Such cutting edges significantly increase the cost of the tool, but these costs are justified by the efficiency of work and the long life of the drill.
The design of the drill on the cutters has a serration located along the entire annular cutting rim. The advantage of such a tool is that during operation, the drill itself and the surface of the workpiece are less exposed to overheating. In addition, all modern Forstner drills having a diameter of more than 25 mm are available with gear rims.
In addition to the above modifications, Forstner drills with a removable tip are found. Such a tool reduces the risk of perforating when drilling a blind hole in workpieces.
As a rule, the size range of a Forstner drill starts from a minimum diameter of 10 mm. Such sizes are little in demand among masters because of their specificity of use, if we compare them, for example, with the most common diameter of 35 mm, which is used when installing door furniture and locks. In construction stores you can easily find drills with diameters of 50 and 55 mm, as well as 60 mm. It is noteworthy that diameters ranging from 15 to 26 mm have a shank of 8 mm in size, and for larger models of milling cutters with a working diameter of 28 to 60 mm, the shank has a slightly larger size and is already 10 mm.
How to choose?
The choice of the Forstner cutter depends on the tasks that you have to perform with it. In carpentry workshops or in production, this is a frequently used tool where various drill diameters are used, so for such intensive use it is advisable to have a complete set of the right sizes. As for domestic use, the drill is purchased to perform a specific task, then it is rarely used. In this case, there is no need to buy a set of expensive tools, since the costs may not pay off.
To purchase a quality Forstner drill, you need to pay attention to several main signs:
- the original drill model has small round holes in the center of the working part;
- the cutting blades of the milling cutter interrupt the annular rim only at two points located opposite from each other;
- original drill blades can only be sharpened manually.
Forstner’s original drill models are made only by Connecticut Valley Manufacturing, the only American company in the world. Here, each part of the tool structure is machined separately from the steel billet, and the alloy contains an admixture of carbon, while other manufacturers make each part of the drill a casting method followed by assembly of the finished parts. The real Forstner cutter has a thicker cutting part than its counterparts, so this tool is less prone to overheating and rotates faster, making it possible to work at high speeds of the power tool, while maintaining the quality of the hole machining at the highest level.
In the process of choosing Forstner cutters, you need to pay attention to the appearance of the state of the cutting edges. It often happens that manufacturers pack their products in opaque packaging. In such cases, it is impossible to consider and evaluate the details of the tool, so you run the risk of acquiring low-quality goods, which, when the package is opened, may be buried, chipped or deformed.
It is unrealistic to fix such significant drawbacks with the manual sharpening method, since the geometry of the drill design will be violated, so it is better to refuse to buy the product in opaque packaging.
The use of the Forstner drill is simple. Having picked up the tool, the centering protrusion is brought to the planned center of the future hole and slightly press the tip into the thickness of the material. It is necessary to press in such a way that the annular cutting part of the drill lies flat on the working surface. Then you can start the working process, but first they start drilling at low revolutions of the drill, gradually increasing speed. Drills are designed to work with them at a maximum of 1800 rpm. The basic rule of work during drilling is as follows: the larger the cutter size, the slower it should rotate. Such a low-speed mode is necessary in order to save the cutting edges of the tool from melting and dulling when it overheats.
In addition, at too high revolutions, the likelihood of a drill breakdown from the intended drilling working area becomes more frequent. If you need to protect yourself in order to make the hole very accurately, at a given depth, it is best to use a cutter with a limiter for this purpose. This device will stop the drill in time and protect the material from perforation, but you will have to work at low speeds. When drilling a blind hole in a thin-walled workpiece, experienced craftsmen recommend using 2 Forstner drills at once. Begin work first, outlining the area of the working hole, and finish with another, which previously sharpened sharp ledge. Thus, the cutters will not be able to cut through the material as deep as a conventional drill does.
How to sharpen?
In the process, any, even the highest quality, drill gets dull. Original products can be sharpened manually, and sharpening non-original analogues can be performed on a grinder. Sharpening the Forstner mill, experts are guided by certain rules:
- the cutting part of the annular rim is not sharpened manually - this is done only on grinding equipment;
- grind the cutters to a minimum so as not to change the geometry and proportions of their working surfaces;
- internal cutters sharpen with a file or grindstone.
High-quality, but expensive products with a thin titanium coating do not require frequent dressing or sharpening and effectively last longer than their inexpensive counterparts made of ordinary steel.
In the next video, you will find an overview and testing of Forstner Protool ZOBO drills.