Rack with milled teeth: for efficient and performing machines

When we talk about a rack with milled teeth, we refer to a device combined with a toothed wheel that aims to obtain a continuous linear motion from an originally rotating motion.

It is a major component in many mechanical productions: as we shall see, the scope of application of the racks with milled teeth embraces the industrial machinery sector, with particular regard to precision with high stresses, plasma cutting and waterjet In the automotive industry, the racks with milled teeth are used for steering systems.

Some companies also use them for the transfer of non-fixed bridges.
The difference between the racks with milled teeth and the cylindrical gears lies in the maximum force that can be applied to the tooth and this is because no twisting movement is applied to this transmission element. The most important element of the rack is represented by the milled teeth that allow them to be used in one area rather than the other.

These adjustments follow the same rules applied to the gears to become finished profiles or pre-milling that incardinate them in specific categories.
The machining of this rack involves an initial step of creating the teeth made with a type of cutters similar to creators, but without the continuous thread towards the external diameter, to pass, to the heat treatment and then move to the phase of milling the teeth. There are, for example, cutters capable of cutting two teeth at a time with high speed: these are tools with a considerable diameter that in some cases can reach up to 200 millimetres.

Their length also varies according to the power and capacity of the module of the teething and milling machine, to obtain optimal milling both from the point of view of precision and the finished product’s quality.

Compared to the past, today the racks with milled teeth are used in many sectors of the industry and that is why they are of different sizes, as well as the modules, differentiated according to the levels of precision that are intended to be obtained.

Modules: a variety of sizes

Thanks to the wide use of racks with milled teeth, the available modules can be catalogued according to the width. Among the most performing racks that are on the market today, you can find modules that reach even over 90 millimetres, with the ability to transmit force levels of thousands of Newtons.

For an approximate list, we could say that racks with milled teeth are used:

• to make automatic loaders or other commonly used machine tools;
• certain types of steering gear mounted on cars;
• production of high-precision measuring devices, such as medical devices or numerical control machines also used in hospitals;
• some machinery used in the graphic and textile sectors.

Due to the wide use that is made of these racks today and thanks to the wide range available on the market, it is possible to obtain unlimited lengths by assembling racks with different lengths.

The machining of this type of rack takes place in consecutive steps: the milling cutter plays the role of cutting a certain number of teeth and then moves along the axial axis of the rack for a precise value that must correspond to the number of steps inserted into the milling cutter. After the milling phase, we proceed to cut another series of teeth and the subsequent milling, giving life to a proper production chain.

In the production process, the movement must take place extremely precisely; this can only happen using numerical control.

Types of racks with milled teeth: straight teeth or helical teeth

Racks with milled teeth can come in two types: straight teeth or helical teeth, these are different production methods that do not involve any change in the precise profile of the cutter. The latter is always positioned in the section of the normal teeth, reaching the purpose for which it was designed.

When the helical rack is moved along the axis, following the milling of a group of teeth, the distance of the displacement will correspond to the number of steps of the milling cutter that concern the normal section divided by the cosine belonging to the angle of the helix.

A problem that often occurs during the production of racks with milled teeth is their deformation due to heat treatment. The high temperatures cause a twist, or a curvature, called a bend, which assumes different values and damages depending on the rack’s length. To avoid this problem, high precision is required to carry out modification operations with super metals suitable for the milling to be carried out.

The case of short racks or those that require limited levels of precision is different: in these cases, the teeth are ground directly with milling. To understand the machining technique, it is necessary to consider that rack cutters with milled teeth are not equipped with a standardised profile, which is defined by the pressure angle and the module.

For this reason, it is very common that the same milling cutter is necessary to produce different racks with different precision characteristics and variable lengths.

New technologies in the field of racks with milled teeth: innovation and high automation

In the different production phases to which the rack is subjected, the different rack teeth may have to be milled, which requires different treatments such as a finished profile for one and pre-milled teeth for the other: in these cases, the high automation and the cutting-edge machinery manage to obtain the same pressure angle, the same module and two different types of milling. This is a truly remarkable result that has only been possible for a few years thanks to the advances that technology has made in the field of production systems.

Many rack manufacturers consider it necessary to reduce the number of types of cutters to be stored in the warehouse, for this reason, they make requests to the primary manufacturers to build a single finished profile able to penetrate more, performing the tooth milling in an increased way.

Only in this way it is possible to reduce the processing phases, optimising the processing times to obtain a perfectly executed product, without defects and usable immediately without further modifications.

Rack with custom-milled teeth: precision and customisation

Racks with milled teeth are the classic elements used to transmit the translational movements and mechanical rotation between the different parts of the machines and motorcycles. This factor explains the enormous diffusion they have had in recent years and the increase in commercially available types.

The main concern of industrialists who need tooth milling is to find products made with the highest quality material to last a long time and able to maintain very high safety standards. But not only that, the needs of modern industry are much more complex than in the past and require precision, resistance and perfect finish to be ready for use without the need for further treatments. It is not possible to offer generic products of average quality but racks of different sizes to meet the most diverse needs of the industries.

Aware of these needs, Officine Meccaniche Zanatta is a reference point for the design, production and sale of racks with milled teeth throughout Italy: it offers a wide range of racks suitable for various needs, as well as standard series combined gears, all characterised by a very high-quality level. Each gear is made of carbon steel standardised in modular sizes according to DN 3962/63/67 to ensure a complete connection at the base of the tooth with a significant increase in flexion and resistance.
The systematic use of this new generation of Numerically Controlled Teething. Machines ensures custom tooth milling, which meets the precision standards required by DIN 3962.

By visiting www.officinemeccanichezanatta.com you can find a wide range of models suitable for the most diverse needs, with different adjustments to ensure maximum quality, precision and durability over the years.