The grinding evolution from the Prehistoric time to the present


Grinding has been employed in manufacturing for more than 100 years although the earliest grinding practice goes back to neolithic times thanks to the Homo Sapiens activities. Size reduction is infact the oldest engineering process started right in prehistoric times.

As the years go by there is an evolution from stones, mortal and pestle, saddlestone mill, larger querns driven by animals, water wheels until the 20th century that is defined as the modern grinding process birth. Indeed, the grinding process achieves his scientific basic from 1914 thanks to the seminal publications by Alden and Guest. Since then grinding is defined as a machining process thant employs an abrasive grinding wheel rotating at high speed to remove material from a softer material.

Nowadays in modern industry the grinding process is carried out thanks to machine tools which combine computer-controlled feed-drives and slide-way motions, allowing complex shapes to be manufactured free from manual intervention.

Grinding evolution has also increased grinding wheel speed and removal rates: they boosted by two to ten times over the last century.

Also the abrasive types have evolved by ensuring advances in productivity. As a matter of fact, new ceramic abrasives based on sol gel technology have been introduced together with the development of superabrasive cubic boron nitride (CBN) and diamond abrasive based on natural and synthetic diamond.

Productivity has also been increased thanks to the insertion of new grinding fluids and methods of delivering grinding fluid. These fluids have also been an essential part in achieving higher removal rates and maintaining quality.

In recent years, grinding evolution has passed through the inclusion of high-velocity jets, shoe nozzles, factory-centralized delivery systems, neat mineral oils, synthetic oils, vegetable ester oils and new additives. Minimum quantity lubrication provides an alternative to flood and jet delivery aimed at environment-friendly manufacturing.

Thanks to all of this innovation, today grinding is a key technology for production of advanced products and surfaces in a wide range of industries.  


Replace older systems with innovative solutions: Bonfiglioli and the GR250 grinding machine.


Bonfiglioli recently renewed part of its machine inventory to maximise production efficiency in its Bologna plant through the reduction of downtime. To meet this need, Samputensili responded with two dual table GR 250 Grinding Machine for grinding worm screws.

Reducing downtime

Producing a wide variety of high quality products at elevated production rates is possible thanks to the use of cutting-edge machine tools. This is why Bonfiglioli has always invested in the purchase of technologically advanced solutions, and precisely in this regard it recently installed two Samputensili GR 250 grinders for worm screws.

“Our philosophy is to periodically update our machines to replace the older systems with innovative solutions that allow us to increase the efficiency of the process” explains Mauro Nanni, Operation Engineering Manager of Bonfiglioli. “As far as machine tools are concerned we rely on just a few suppliers that have been carefully selected, including Samputensili. We have been working with them for a very long time, and it could not have been otherwise considering the fact that Clementino Bonfiglioli worked in Samputensili before founding Bonfiglioli Riduttori, and therefore knew very well both the technologies developed and the manufacturer’s approach to its customers”.

Thanks to this long-established partnership, Bonfiglioli turned to Samputensili for the replacement of some of the machines that have become old and inefficient. “One of our goals was to increase productivity without disturbing the machine’s operation, reducing the downtimes while processing the entire lot”, explains Nanni. “To meet this need, Samputensili proposed the GR 250 Grinding Machine worm screw grinding machines equipped with a dual table, making it possible to perform operations while the machine is running that are not of added value like loading/unloading pieces or measuring components. These operations therefore do not affect production times, and the productivity of the whole lot is higher”.

Dual table, maximum efficiency

In industry, the success of a family-run business depends largely on the will of the founder to invest constantly in the acquisition of new production technologies. An approach that has allowed many Italian entrepreneurs to start small businesses that have evolved over the years into top global players. This is the case for Bonfiglioli, a company based in Emilia-Romagna, specialised in the production of fast gearboxes and gear motors, that has become one of the world’s leading companies in the trade.

Evolution of the company

Bonfiglioli’s story began in 1956 when Clementino Bonfiglioli decided to start a business machining gears intended primarily for agricultural machines and motorcycles. These were two sectors that were difficult to manage due to their seasonality, which made precise production planning difficult. For this reason, after a few years Bonfiglioli decided to approach the steadier and appetising industrial sector, manufacturing gearboxes and gear motors. This was a move that made it possible for the company to grow steadily over the years thanks to a series of strategic operations aimed at expanding the product portfolio and, consequently, the customer base. Over the years, important acquisitions of companies in Italy, like Trasmital and Tecnoingranaggi, and abroad, like the German Vectron and O&K Antriebstechnik, have allowed for an expansion of its production portfolio and completed the range of gear motors and electronic drives produced in both size and function.

In 2016 Bonfiglioli presented its EVO project, which calls for an expansion of the facilities in Calderara di Reno to 58,500 sq.m. of surface area, bringing together all the production activities that today are performed in various locations in the Emilia region. An investment of €60 million that will employ 600 employees, producing 800,000 units per year. The new structure will incorporate all the principles of Industry 4.0 and will act as a benchmark production plant for further developments in other Bonfiglioli facilities worldwide.

Global partner

Today, the company is directly present in 16 different countries around the world, with subsidiaries and manufacturing sites employing a total of 3,700 people.

The turnover of €789 million in 2016 demonstrated significant growth compared to the €730 million of the previous year. A growth driven by the Asian market, with China and India in the lead, followed by other points of excellence like Brazil and the United States. Customer profile: Bonfiglioli Germany, Italy, France and Spain represent the major EMEA markets, together accounting for 55% of turnover.

“From the point of view of production, we have two business areas: Mobile&Wind and Industrial”, explains Massimo Sarti, Bonfiglioli’s Strategic Marketing and Communication Director. “Mobile and Wind sectors have been combined into a single business unit because they have much in common. The technology behind the products used in these areas is similar, as is the business model. In fact, we deal with a small number of very large customers who operate on a global basis. For our industrial customers, we have an area dedicated entirely to the construction of industrial gear motors and another focused on electronic and mechatronic products, both destined for a wide range of applications: food processing machines, packaging and packing, transport on belts, automatic warehouses, rubber and plastic extruders, textile, woodworking and many others”.

“Most of the products made for the industrial world is modular”, continues Mauro Nanni, Operation Engineering Manager of Bonfiglioli. “In our production facilities, we produce lots with high volumes of various components for gearboxes and gear motors. Depending on the specific needs of the end user, we ‘construct’ a solution that is custom designed but equally reliable and functional, precisely because the single components used are standardised, therefore widely tested and optimised”.

What is a gear shaving machine?

Gear grinding machine

Gear shaving machine is a solution used in the finishing operation of an external spur and helical gear. It is also possible to shave an internal gear, although generally the work conditions are less favorable. The shaving process can improve the quality and precision of a hobbed gear of 3 classes. However, the final results depend not only on the accuracy with which the shaving cutter and the gear shaving machine is designed and manufactured, but also on the quality achieved  with the prior machining.

Gear shaving is still today the most widely used method for the finishing of gear teeth, especially for the continuous production of large lots, since it represents the best cost/performance ratio. The main limit of the gear shaving process is the lack of the chance to remove the distortion caused by heat treatment. Usually, when high noiselessness and strict quality levels are strictly required, the grinding operation is the best solution, although obviously more expensive.

In the automotive industry, the vast majority of gears used in gearboxes are suitable for gear shaving. The productivity of a gear shaving machine is much higher compared to a gear grinding machine. The gear shaving operation is composed by the simultaneous rotation of workpiece and cutter as a pair of gears with crossed axes. The crossed axes generate a reciprocal sliding action between the flank, gear tooth and the cutter teeth.

Gear shaving should be carried out using extremely precise gear shaving machines and tools. That is why it is essential to rely on companies with broad and proven understanding of gear technology with a particular focus on innovation and development, so that they can offer the best cost effective solution on the market for your specific needs.

Samputensili Machine Tools has an excellent reputation in the gear shaving machine industry thanks to its brand SICMAT. The SICMAT product range includes the famous RASO 200, RASO 400 and RASO 600. They are all synonymous of quality, excellent performance and high reliability since the ‘80s.

What is the Archimedean spiral in a gear hob?


An important element of the gear hob design is the tip which represents a relief of the tooth profile and a part of the Archimedean spiral.

The Archimedean spiral is a curve traced out by a point moving in such a way that its movement towards or away from the center is uniform with the increase of its vectorially angle from the starting line. This curve is used  to ensure the continuity of the tooth profile during the resharpening.

For a resharpening with a zero-rake angle, the cutting profile lies on a plane that passes through the hob axis and the Archimedean spiral must ensure that the profiles that are on this perpendicular section are constant. This curve is used in the tooth profiles of the gear hob.

Archimedean spiral - gear hob design

The characteristics of the Archimedean spiral are:

  • In Archimedes spiral, any ray passing through the origin does intersect successive turns of the spiral with a constant distance which is equal to 2 π Therefore, it is also named “arithmetic spiral”.
  • An Archimedes spiral, there are two arms – one arm for θ> 0 and another for θ < 0. These two arms are connected to the origin. One arm is shown in the graph. If we take the mirror image of this arm along Y axis, the other arm will be obtained.
  • Usually the term Archimedean spiral is used for more general spirals. The normal one occurs when in its equation, n = 1. Other spirals that fall into this group are the Fermat’s spiral and the hyperbolic spiral.
  • All the static spirals are logarithmic spirals in nature, except for Archimedes spiral.


What is a gear dry grinding?


Gear dry grinding is the new state-of-the-art process for gear manufacturing thanks to the elimination of cutting oils during the process, gear dry grinding has marked an important breakthrough.

In the last years, a constant attention towards global environment has affected all sectors of our lives, including mechanical engineering. Thereby, many manufacturing companies have invested in R&D in order to design and manufacture more sustainable and environmental friendly solutions.

Gear dry grinding, carried out by the SG 160SKYGRIND, has been presented for the first time at the EMO 2015 in Milan by Samputensili Machine Tools. Thanks to this innovative machine, it is now possible to have a completely dry production when manufacturing gears.

Gear dry grinding is an extremely productive process. Most of the stock allowance is removed through a skiving hobbing tool in the first phase, and in the second phase a grinding wheel removes the rest. Both phases do not cause any problem of overheating the workpiece, thus enabling a complete elimination of cutting oils. Moreover, the gear dry grinding machine SG 160 SKYGRIND has a state-of-the-art structure made up by two work spindles moved back and forth through independent linear motors for a quick workpiece changeover. This machine configuration ensures a chip-to-chip time of less than two seconds.

The gear dry grinding machine has a very small footprint and is extremely environmentally-friendly.

The main advantages of gear dry grinding are:

  • No cooling oils needed, with a consequent saving of up to 30% of machine maintenance costs
  • Reduced environmental impact and a safer working place
  • Same performance as traditional process at lower costs

To have more information on the topic or to contact directly our sales managers, visit the page


Discovering all the parts and elements of gear hob

Gear hob Samputensili

A gear hob is a gear cutting tool composed of different parts. The main parameter characterizing a gear hob is the module, which is the result of the division between the pitch gear diameter and the number of the teeth.

Another element of the hob is the pressure angle which coincides with the nominal pressure angle of the gear. The normal pressure angle αn – measured on a section perpendicular to the direction of the thread – and the axial pressure angle αt – measured on an axial section of the hob – are easily distinguished.

Besides, helix angle β, also called thread angle, is measured on the pitch diameter of the hob depending on this value and the number of starts. The angle is direct proportional to the diameter, pitch, module and number of threads. So, when this increase also the other parameters increase consequently. It is important to highlight that the helix direction of the hob is chosen in agreement with the helix direction of the gear.

Gashes are another fundamental geometrical element of a gear hob. These are serrations that cut the threads either in an axial or in a perpendicular direction. The number of gashes should be chosen during the design phase on the basis of many factors, including final quality and working conditions. They depend on the hob diameter and on the number of starts. The current tendency is to design hobs with a larger number of gashes due to the fact that the hobbing time is reduced and the feed speed is higher. Moreover, the gash determines the cutting face by intersecting the thread. The cutting face is radial in the majority of cases. In any case, to realize a positive or negative rake angle, the hob must be reshaped with a grinding wheel positioned out of axis by a distance that depends on the rake angle itself and on the hob diameter.

There are also other important gash’s elements which influence the cutting efficiency of the tool, just like:

  • the tooth back angle;
  • the bottom radius of the gash;
  • the gash depth.

These are just some of the most important elements of a gear hob, to know the others read the news.