Step drills have, as the name suggests, different steps that cut the desired diameter. Before we take a closer look at the characteristics, we would like to briefly go into the term "CBN process".
If you read texts about step drills on the Internet, you will always stumble across the abbreviation CBN. But what does it mean when step drills are produced using the CBN process?
CBN stands for cubic crystalline boron nitride. Boron nitride is a chemical compound of boron and nitrogen. The addition "cubic" describes the crystal structure of the chemical compound. CBN is much harder than conventional abrasive materials such as silicon carbide or corundum and is used for grinding hardened high-speed steels (HSS).
This also applies to us.
The head of step drills can be compared to the head of twist drills. Centering in the workpiece should be as easy as possible with both drills. The point angle is responsible for this.
The point angle is located at the head of the step drill. The angle between the two cutting edges is measured at the point. As already mentioned, a point angle is required so that the step drill can center itself in the material.
Our step drills have a small point angle of 118° and requires less pressure when centering in the material. The larger the point angle, the higher the contact pressure and the centering in the material requires more pressure.
In our article "8 features of a twist drill and its functions" we discuss the point angle in more detail.
Point cuts and point thinnings
For easy tapping, the step drill requires a corresponding pointing in addition to the small point angle.
The various points are standardized in DIN 1412 shapes. The most common form for step drills is the split point (shape C).
Step drills with shape C center perfectly in thin sheet metal and are suitable for drilling in solid and high-alloy steel. The point cut is also ground using the CBN grinding process.
The drawing shows the point cut of a twist drill from the side and from above. The point cut of step drills and twist drills is the same.
Further information about the different forms can be found in our blog post " Point cuts and point thinnings of twist drills for metal cutting".
Profile of flute (groove profile)
The groove profile serves as a channel system for collection and for chip removal. It is important that the chips are removed quickly, as otherwise high heat will develop and the drill will burn out. Non-breaking chips in particular are transported easily, as with a twist drill.
Step drills can have spiral and straight grooves. With the spiral groove, chip removal is much better than with the straight groove. The service life can be significantly extended by good chip removal.
Due to the CBN-deep-ground spiral grooves, the blades, in contrast to the conventionally milled flutes, are burr-free and sharp. This reduces the formation of built-up edges and cold welds on the cutting edges, resulting in a significantly higher cutting performance.
The step angle of step drills is 90° and defines the transition from step to step. The transitions between the individual steps should be as easy as possible and hardly noticeable.
The step transitions are used to chamfer or deburr the hole when the desired diameters are reached.
Number and diameter of steps
Step drills are indicated in sizes. These sizes determine the diameters and the number of steps.
A step drill size 1 has nine steps with different diameters between 6.0 and 20.0 mm (see picture).
Step drills are ideal for sheet metal working and are suitable for cutting non-ferrous metals, stainless steel sheets up to a thickness of 1.5 mm, thermoplastic and thermosetting plastics and all current steel sheets up to a thickness of 4.0 mm. You can tap, drill and deburr in one step with the step drill.
They are mainly used in the sectors of industries
- electrical (size 4 + size 9),
- sanitary engineering and heating technics (size 6 + size 7),
- automotive, mechanical engineering, aviation (size 0/5, size 0/9, size 1, size 2, size 3, size 5) and
- switching systems (size 0/9k, size 1k, size 2k) up to 2,0 mm sheet thickness.
Use coolants and lubricants for cutting metals. By using them you can considerably extend the service life of the step drill.
We carry step drills with tool steels HSS and HSSE-Co 5 and with coatings TiN and TiAlN. Depending on the tool steel and coating, harder or softer materials can be cut.
Conclusion and summary
Step drills are ideally suited for cutting metals, plastics and wood up to 4 mm, for stainless steel up to 1.5 mm.
The production of step drills by using the CBN process enables measuring and shear cutting edges due to the higher hardness during the grinding process. The material structure is cut through smoothly by the much harder abrasive material.
The point angle and the point thinning ensure easy centering and a easier tapping into the workpiece. As soon as the step drill has been drilled through, the two or three cutting edges are already in place. The burr-free and sharp cutting edges cut the workpiece and guide the chip over the groove profile.
The step angle is 90° and determines the transition from one step to the next. The transitions are used for chamfering or deburring the hole.
Step drills are available in various variants in the tool steels HSS and HSSE-Co 5 and the coatings TiN and TiAlN. You can find our complete product range of step drills under Products > Step drills.
If you have trouble finding the right step drill, please do not hesitate to contact us.