Author: mariaelena

Factors which influence gear tooth bending stresses

gear tooth bending stresses

Modern gear design must consider different factors which can have an impact on it other than the one included in the Lewis equation as:

  1. Pitch line velocity: Greater the linear velocity of the gear teeth is and greater is the impact of successive teeth as they come into contact. These impacts are caused by the impossibility to design a absolute perfect tooth profile since deflections are inevitable.
  2. Manufacturing accuracy: this has a great impact on loading. Moreover, it determines whether teeth share the load when pairs of teeth are theoretically in contact.
  3. Contact ratio: for gears with 1<G<2, the transmitted load is divided by two teeth pairs each time a contact occurs. It is important to take into consideration that there are two loading conditions:
    • Part of the load at the tooth tip
    • The whole load at the point of highest single tooth contact.
  4. Stress concentration
  5. Degree of shock loading
  6. Accuracy and rigidity of mounting
  7. Inertia moment of the gears and attached rotating members: Momentary angular accelerations and decelerations of rotating members are caused by small tooth errors. With large inertia, rotating members tend to resist acceleration, causing large momentary tooth loads. It is possible to reduce the harmful inertia effect using the torsional elasticity.

Moreover, the gear tooth bending fatigue issue needs an evaluation of the following points:

  • Fluctuating stresses in the tooth fillet
  • Fatigue strength of the material          

Gear-bending strength calculations are commonly based on the assumption that the tooth-bending fatigue strength has a normal distribution with one standard deviation being about 8 percent of the nominal endurance limit.

Gear nomenclature


Gears are special devices which transmit rotary motion from one shaft to another. They can have external or internal teeth and can be shaped in different forms according to their axis position such as:

  • Intersection axes: bevel gears
  • Parallel axes: helical gears
  • Non-intersecting: worm gears

In order to have a greater understanding of gear production and finishing process it is important to know the nomenclature of gears and all related terms. Below we have tried to offer a synthetic overview of the main parts and the nomenclature of the gears.

Let’s discover the nomenclature of the gear

gears nomenclature

There are four circles to keep in mind:

  • Addendum circle: The outer circle touching the outermost points of the teeth
  • Pitch circle: The imaginary rolling circle produced during rotation by mating gears
  • Base circle or root circle: The circle from which the involute tooth profile is developed
  • Dedendum circle: The circle touching the bottom of the tooth profile

Other main parts of the tooth profile:

  • Addendum: The radial distance for which the tooth profile is extended outward beyond the pitch circle from the pitch circle
  • Dedendum: The radial distance for which the tooth profile is extended inward from the pitch circle from the pitch circle
  • Pitch Point: The point of tangency of two gear Pitch Circles, through the Line of Centers.
  • Line of Action: A line tangent to the Base Circles of mating gears, through the Pitch Point and thus the path of tooth contact.
  • Pressure Angle: The angle formed between the Line of Action and a line tangent to the Pitch Point.
  • Tooth Thickness: The thickness of the gear tooth measured along the Pitch Circle.
  • Circular Pitch: The length of the arc along the Pitch Circle between corresponding points of adjacent teeth.
  • Face Width: The width of gear tooth measured axially.
  • Tooth Face: The mating surface of a gear tooth between the addendum circle and the pitch circle.
  • Tooth Flank: The mating surface of a gear tooth measured between the pitch circle and the base circle.
  • Backlash: Amount of clearance between mated gear teeth.

Together to boost recovery

Sampingranaggi sponsor Inmotion GP

We are glad to have been event sponsor of the event “Together to boost recovery” (Insieme per accelerare la ripresa), which took place in in Modena, Italy at the Casa Enzo Ferrari Museum on June 14th and was organized by ASSIOT and ASSOFLUID.

It was an important opportunity to talk about the manufacturing sector of gears, gearboxes and power transmission systems in general, an Italian excellence of which little is known, and even less said.

The aim of the conference was mainly to stimulate the debate among the leading opinion leaders on the major challenges faced by the industry in the coming years, such as technology integration, additive manufacturing and connected business.

The event will end with the first edition of the “Grand Prix InMotion”. At 6:00 p.m. all attendants will join the fray at the authordom of Modena challenging powerful cars, such as Ferrari F458 Challenge and KTM X-Bow. Thereafter, an informal dinner and open bar has been set in order to promote networking and coopetition among parties.

The Sampingranaggi team, composed by our President Antonio Maccaferri, the General Manager Marcello Stradini and the Gearbox Engineer Mario Monticelli, has attended the whole event.

Below you can find some images of the event.

Marcello Stradini new General Manager

Marcello Stradini Sampingranaggi

We are pleased to announce the appointment of the new General Manager of Sampingranaggi, Mr. Marcello Stradini.

Born in Genoa (Italy), Mr. Stradini graduated in Mechanical Engineering from the University of Genoa and has an Executive MBA from the University of Bologna. He has matured longstanding experience in the automotive industry, having worked for FCA in different plants and positions for over 10 years. Subsequently, he has worked for several multinational companies, establishing an accomplishments-driven career highlighted by rapid acceleration to increasingly responsible positions, up to the last one of General Manager at Cementir Italia S.p.A.  

“It is my privilege to join Sampingranaggi and the entire team”, Mr. Stradini stated. “I am very excited to build on the strong tradition and excellent reputation they have set forth and help in the continued growth of Sampingranaggi.”

The new General Manager is renowned for his technical and organizational competences and will boost the company’s competitive level in an ever-demanding worldwide market. The CEO of SAMP Group, Lapo Vivarelli Colonna, said: “We welcome Marcello Stradini in his new and prestigious position. He is joining the team to help us grow in the gear and gearbox market in terms of competitiveness, sales volume and market share.

We therefore take this opportunity to welcome Mr. Stradini on board and wish him every success.

SI China got ISO 9001 certification


Sampingranaggi China has been certified ISO 9001 for gears and gearboxes manufacturing. We are glad to announce this important achievement of our Chinese subsidiary to all our stakeholders.

ISO 9001:2015 sets out the criteria for a quality management system. This standard is based on a number of quality management principles including a strong customer focus, the motivation and implication of top management, the process approach and continual improvement. Using ISO 9001:2015 helps ensure that customers get consistent, good quality products and services, which in turn brings many business benefits.

This is an important result of a year teamwork on the analysis and revision of the quality procedures and their implementation.



Sampingranaggi OMNI gearbox

We are glad to introduce you our brand new OMNI gearbox.
OMNI gearbox is our innovative patent-pending line of high–precision planetary gearboxes. It stands out for its extraordinarily compact design and meets the increasing market demand for: flexibility and customization; robustness and reliability with minimal maintenance.

It  is the perfect solution for all applications requiring high precision, stiffness and lightness, and is available in a wide range of sizes and ratios.

Sampingranaggi will be at the Hannover Messe, visit our stand hall25, F33; there you will be able to see closely the OMNI gearbox and ask all information related to our team!

For more information click here or enjoy the video

Hannover Messe 2017

Sampingranaggi Hannover Messe 2017

We are glad to announce our participation to the Hannover Messe (April 24 – 28, 2017) which will take place at the Hannover Exhibition Grounds, Germany. We look forward to meeting clients, partners and friends and share the latest news concerning new developments, investments and more!

Visit us at Hall 25, Booth F33!

SAMP celebrates 80th years!


This year SAMP celebrates its 80th anniversary.
When the company began in 1936, the original 15 employees in our first building – a small factory in zola Predosa, near Bologna (Italy) – could not have foreseen that 80 years later, their tiny little business would be a global company operating across 5 continents.

We would like to express our gratitude to the thousands of machine operators, service technicians, engineers, employees and managers that have served our company with loyalty and commitment over these 80 years. As we continue to build a stronger company thanks to the new acquisitions and partnerships worldwide, we fully recognize that our people are the foundations of our long and fruitful success story.

Below some images from the 80th Anniversary dinner

Sampingranaggi at the CIIF 2016

Sampingranaggi at the CIIF 2016

We are glad to announce our participation to the China International Industry Fair (CIIF). The 18th session China International Industry Fair or CIIF 2016 is going to be held from 1 to 5 November 2016 at the National Exhibition and Convention Center of Shanghai. CIIF 2016 will comprise eight Theme Shows under one roof and occupy 260,000 sq. meters as its display area. According to CIIF source over 2,000 exhibitors and 120,000 trade visitors are expected to attend the event.

Since its launch backdated in 1999, CIIF has become one of the most influential international industry brand exhibition in China representing a great window and platform open to the world of manufacturing for international trade, communication and cooperation on industrial scope.

A number of innovative gears and gearboxes for different applications for robotics will be on display on our booth. We will show also gears for other applications like timing gears and gears for air compressors, industrial machines, textile machines, printing machines and construction machines.

Expert engineers will welcome all the persons interested on our products and sectors. They will analyze with you the applications and the solutions to your needs.

Sampingranaggi looks forward to meeting clients, partners and friends to share the latest news concerning new developments, investments and more!

Come to visit us at booth B001

SAMP Group also on Instagram

SAMP Group instagram

We know, it took a little while, but finally we are on Instagram! Come and join us on Instagram for beautiful photos, unique behind-the-scenes pictures and more.

Instagram is our new way of making you aware about our work and trying to give you different points of view on engineering in general.

In the SAMP group Instagram account you will also be able also to admire art photos from the SAMP Award of the previous years. The SAMP Award has been organized in collaboration with “Accademia di Belle Arti” of Bologna. It ran for 3 editions (2006-2008-2012), and for each of them the students of the prestigious art academy were challenged to create their best artworks on a specific topic. The first edition was about gears, the second one on wire and cable and the last edition students had to design a project to decorate a white wall of the new SAMP’s plant in Bentivoglio.

So if you like photography, engineering and art in general do not hesitate to follow us. Do not be passive, use Instagram to communicate with us, sharing your engineering art or suggestion. How to do it? Easy, use #SAMPGroup or #beyondprecision ! We will be happy to share your artworks and take suggestions.

“The whole point of taking pictures is so that you don’t have to explain things with words” – Elliott Erwitt

Click here to access to our Instagram account