The Library of Thread Rolling 2/9

The history of thread production

Specialist topic: An exciting overview of thread rolling... The basics, processes, tools, and applications of rolled high-tech threads

The thread vert probably replaced the wedge as a fastening element. The realization that a curved surface with grooves provides a greater clamping force than a flat wedge must be very old, as the oldest technical threads found are more than 4,000 years old – chipless production in the days of old.

Clasps found as grave goods were used to hold items of clothing together or to secure pieces of jewelry; these clasps had a short cylindrical core around which a wire was wound in a spiral. They therefore emulated the principle of fastening screws with a chipless shape.

There are hardly any fastening screws in the modern sense from ancient Greece and Rome that have been found. However, with power screws the situation is different. Greek mathematician Archimedes of Syracuse (ca. 287 to 212 BC) is credited with inventing the screw conveyor. Because the Archimedes' screw is simple and sturdy, it was used to draw water. Today, this power screw is mostly used for conveying sewage sludge or as an extruder in plastics processing machines.

Machined, one-off production from antiquity...

Roman doctors used very fine surgical instruments with two screw spindles, i.e., threaded spindles with a matching nut, to further open wound openings. The bronze threaded spindles were first cast as a rough shape and then filed. Since the threads were even and easy to move, they can be described as precision mechanical products. The associated nuts – often the yoke of the instrument – were also cast and ground onto the threaded spindle. The nuts could not be replaced.

Antique construction cranes, and oil and wine presses had wooden screw spindles, usually made of oak. The engineers at the time chose large core diameters and pitches not only because of the forces involved, but also because of the low strength of the wood. This was the only way to prevent the wood from splitting across the grain. In order to apply threads with a uniform pitch to such large spindles, a triangular sheet metal template was bent around the cylindrical blank and the course of the thread groove was marked. For the next turn, the template had to be shifted by the height of the thread pitch and applied again. The process of making threaded grooves was part filing and part whirling; they were cut by hand, which was a very simple yet also sufficiently precise principle for that time.

...through the Middle Ages...

At the start of the Middle Ages, technical achievements were lost, as were many of the intellectual findings from antiquity. Like the spoked wheel, the screw also largely disappeared from everyday life. There were just a few forging workshops where blanks were forged, filed, and then hardened to make fastening screws, but only as individual pieces for a very specific purpose, or for personal use.

It was not until the Renaissance that technology began to move again. The construction of cathedrals, minsters and especially domes required devices for lifting heavy loads. Power screws – albeit still wooden ones – were increasingly being used again. We know that during the construction of the cathedral in Florence, the ball-bearing screw spindle was developed. As the forces to be transmitted increased and the space for ever larger constructions was not available, it was just a small step towards the metal power screw.

...to the Renaissance

The first metal screws were intended for war equipment. Screws for the articulated joints of armor were pre-cast, as in the times of the Romans, and then filed to fit. The tolerances of these threads did not correspond to today's standards, nor were the screws interchangeable.

It was the scholars of the time who, increasingly hungry for knowledge, needed ever more precise physical, astronomical, and mechanical instruments. Optical instruments came from northern Italy, and, north of the Alps, the precision mechanical craft of clockmaking was born. Smaller clocks were urgent required, especially for seafaring, as accurate positioning at sea was only possible by measuring time.

Return to cold forming

Progressive miniaturization demanded fastening screws with threads that could no longer be produced using conventional methods; even filing was too coarse. Threads were being formed in several steps using hardened dies.

Fig. 1: Die for producing threads
(Source: Schreber, D.G. (Hrsg.): Schauplatz der Künste und Handwerke. Bd.9. Leipzig 1769)

High-tech thread...

The industrial revolution in the second half of the 18th century led to a skyrocketing demand for mechanical machine parts. New professions emerged and new – sometimes quite exotic – manufacturing processes were proposed. However, none of these methods was able to eliminate the biggest disadvantage of threads at the time: The screws and the matching nuts were still produced individually and by hand

Getting ready for standardization

However, as mechanization in the mines progressed and railroad construction flourished, people in industry realized that there was an urgent need for interchangeable machine parts. Many people tried to find a solution to this problem, but it was Henry Maudslay (1771-1831) who first succeeded in producing screw spindles with a specific diameter and a constant pitch on his lathe.

The first standard thread

Building on this practical groundwork, Sir Joseph Whitworth (1803-1887) considered the theoretical aspect of threads in order to define unique thread dimensions. In 1841, he achieved a breakthrough by defining the parameters of the outer and core diameters, pitch and flank angle. This year is therefore regarded as the year in which the standardized thread was invented. The thread system, still known today as the Whitworth thread in honor of its inventor, was used worldwide at the end of the 19th century, and thus also on the European mainland. Not even the definition of the meter as the basic unit of length at the Metre Convention in Paris in 1875, and the development of a metric thread system based on it could change it. In the United States, thread manufacturers specified a mixture of English and metric thread sizes. To this day, little has changed in this coexistence of British, continental European, and American thread systems.

Mass production of screws

The standardization of the thread made the screws better, cheaper, and finally interchangeable. Theoretical analysis formed the basis for strength tables for sizing; these replaced the empirical values used up until then by engineers. At the end of the 19th century, screws finally became a mass-produced commodity.

Fig. 2: Jakob Schweizer's automatic lathe (1872) 
revolutionized thread production in the watch industry 

The first attempts to produce threads by forging were made towards the end of the 19th century. Initially, the focus was limited to hot forming. The good flow behavior of the base material was offset by undefined material properties and a poor surface; the strength of the threads also left much to be desired.

The beginnings of thread rolling

Although thread rolling had already been proposed by the American William Keane around 1835, it was too far ahead of the available materials at the time. The available steel splintered during cold forming. Only when steels with sufficient ductility became available, did production become successful. Though the first results still reflected the insufficient knowledge of the relationships between compressive force, deformation, and plasticity. As knowledge of metallurgy increased, however – thanks mainly to aircraft construction – this process received the boost it needed. That's why aircraft construction is considered by many to be the "birthplace" of forging.

Thread rolling on an industrial scale

Thread rolling has only been used on an industrial scale since the end of the Second World War. It is not known which of the thread rolling processes used today was first, but there are some indications it was the recessing or undercutting process. With a little imagination, you can see the resemblance between the tools used for this process and the matrices of Roman antiquity, and the pre-industrial era of the 19th century. The thread pitch is already predetermined by the groove profile of the tool.

Eichenberger – your service provider right from the start

With Eichenberger, you can implement your individual requirements for a screw thread right from the start of development. Don't hesitate to contact us before you even know what you need. We will be happy to work with you to develop a customized solution for your thread system. Contact one of our experts directly, we are there for you right from the start.
> Contact us now without any obligation and find out more

With state-of-the-art production methods, many years of expertise and a tool inventory of over 1,000 rolling tools, we produce rolled screw drives that meet even the most unusual requirements:

• Gradients up to 6x in diameter
• Slope accuracy class G5
• Spindle lengths up to 6 meters
• Spindle diameter from 2 to 160 millimeters
• All standard profiles (M, Tr, UNC, UNF, UNEF, Whitworth)
• Multi-start threads, also as right/left-hand threads
• Steep thread profiles
• Ball screw profiles
• Special profiles
• Worm thread profiles (special quality and price advantages!)
• Serrations and knurling
• Conical thread
• Threads on prefabricated and/or bulky parts, e.g., also on forged parts
• Freely designed thread geometry
• Responding to customer requirements, such as tailored nut geometry
  
  

Eichenberger leaves nothing to chance and places the highest value on quality. This is what has been impressing our customers since 1953. See for yourself!

> 100% Swiss Quality
> Thread specialist since 1953

Fig. 3: Special thread with special profiles according to customer specifications

Literature and sources

The nine blog articles contain excerpts from the Library of Technology, Volume 286, Thread Rolling. This book was compiled with the expert support of Kurt Husistein and published by Verlag Moderne Industrie, ISBN 978-3-937889-30-6.

Kübler, Karl-Heinz, Mages Walter J. Handbuch der hochfesten Schrauben, 1. Aufl. Essen: W. Girardet Buchverlag, 1986.

http://www.hp-gramatke.de/ Hans-Peters Mathematisch-Technisch-Algorithmisch-Linguistisches Sammelsurium.Verein Deutscher Eisenhüttenleute (Hrsg.): Werkstoffkunde Stahl, Bd. 1 Berlin: Springer, 1984. Apel, Heinz: Gewindewalzen: Kaltverformen von Präzisionsgewinden und Spindeln, München: Hanser 1952.

© 2007 Alle Rechte bei sv corporate media, D-80992 München 
Abbildungen: Nr. 1, 23-25 RWT Rollwalztechnik GmbH, Engen; Nr. 2 Foto Deutsches Museum, München; Nr. 3 Musée du tour automatique et d'histoire de Moutier, Moutier (Schweiz); Nr. 16 Fette GmbH, Schwarzenbek; Nr. 18 Meinrad Plaz, Staufen (Schweiz); Nr. 26 Habegger SA, Court (Schweiz); Nr. 34-36 FBT Fahrzeug- und Maschinenbau AG, Thörigen (Schweiz); Nr. 37, 38 Schleuniger AG, Thun (Schweiz); Nr. 39, 40 Max-Planck-Institut für Physik (Heisenberg-Institut), München; Nr. 41 Saurer AG, Arbon (Schweiz); Nr. 42 Line Tech AG, Glattbrugg (Schweiz); alle übrigen Eichenberger Gewinde AG, Burg (Schweiz). Satz: abavo GmbH, D-86807 Buchloe. Druck und Bindung: Sellier Druck GmbH, D-85354 Freising. Printed in Germany 889030.