science

Stackfreed

Stackfreed is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Stackfreed rather than just read about it. In short: A stackfreed is a simple spring-loaded cam mechanism used in some of the earliest antique spring-driven clocks and watches to even out the force of the mainspring, to improve timekeeping accuracy. Stackfreeds were used in some German clocks and watches from the 16th to the 17th century, before they were replaced in later timepieces by the fusee.

Key takeaways

Stackfreed belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Stackfreed to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Stackfreed from memory before moving on to harder problems.

Reference excerpt

A stackfreed is a simple spring-loaded cam mechanism used in some of the earliest antique spring-driven clocks and watches to even out the force of the mainspring, to improve timekeeping accuracy. Stackfreeds were used in some German clocks and watches from the 16th to the 17th century, before they were replaced in later timepieces by the fusee. The term may have come from a compound of the German words starke ("strong") and feder ("spring").

History

Spring-driven clocks were invented around 1400 in Europe. Mainsprings allowed clocks to be portable and smaller than the previous weight-driven clocks, evolving into the first large watches around 1500. However, the early spring-driven timepieces were much less accurate than weight-driven clocks, because they had a source of error weight-driven clocks didn't have. The drive force (torque) exerted by a coiled spring, unlike a weight, is not constant, but is maximum when the spring is wound up and declines as the spring unwinds to turn the movement's wheels. The main cause of inaccuracy in early spring-driven timepieces was the large variation in force provided by the mainspring as it unwound during the timepiece's running period. The force of the mainspring, transmitted through the clock's gears, gives pushes to the oscillating balance wheel which keeps time. The primitive verge and foliot movement used in all early timepieces was very sensitive to the amount of force applied to it, particularly before the balance spring was added in 1658; the weaker the drive force applied by the mainspring, the slower the balance wheel would oscillate back and forth. So without some device to equalize the force of the mainspring, early clocks and watches slowed down drastically during the clock's running period as the mainspring lost force, causing inaccurate timekeeping. Two devices appeared in the first spring powered clocks to even out the power of the mainspring: the fusee and the stackfreed. The origin of the stackfreed is unknown. It is assumed it was invented in the southern Germanic states (Nuremberg and Augsburg) during the 16th century, since the early spring clocks which incorporated it came from there, but it may have been invented earlier. Drawings of stackfreeds appear in Leonardo da Vinci's Codex 1 (1492-1497) and M3 (1497-1499); possibly the device was brought to his attention by his German assistant Giulio. While the fusee went on to become the standard mainspring equalizer in European timepieces, the less satisfactory stackfreed was used exclusively in a few German timepieces; and disappeared after about a century. Surviving examples of stackfreed timepieces date from about 1530 to 1640.

How it works

See drawing. The stackfreed consists of a stiff spring arm (A) with a roller at the end (B) which presses against an eccentric cam (D); usually the roller rides in a groove in the cam's edge. The cam is shaped like a snail. It has a gear on it (E) that is turned by a gear on the mainspring arbor (C), so it makes one turn during the clock's running period. The force of the spring arm against the cam exerts a retarding force on the mainspring, reducing its torque, which varies with the thickness of the cam. When the mainspring is fully wound up, the arm presses against the wide part of the cam. Since it is far from the axis, the retarding force it exerts is maximum. As the clock runs and the mainspring unwinds, the cam rotates and the spring bears against the narrower parts of the cam, reducing the retarding force gradually, to compensate for the declining force of the mainspring. Often (as shown in this drawing) a solid uncut section in the cam's (E) gear teeth also functioned as stopwork, limiting the mainspring so it stopped before it was wound up all the way, and stopped before it unwound all the way. This restricted the mainspring to the center part of its range, further reducing force variation.

Advantages and disadvantages The stackfreed was a very inefficient device. Since it worked by exerting an opposing friction force on the mainspring, it required more powerful mainsprings and higher gear ratios in watches, which may have introduced more variation in drive force. The fusee, the other mainspring compensation device, was much more efficient. The only advantages of the stackfreed were that it was easier to make and much thinner than the fusee, which, combined with the fact that it was located in unused space on the outside of the back plate, allowed stackfreed watches to be flatter. With the development of narrower, more compact fusees, the stackfreed disappeared from timepieces around 1630.

Illustrations

Worked examples

Example 1 — a first encounter with Stackfreed

Start with the simplest possible case. Write down what Stackfreed claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Stackfreed before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Stackfreed ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Stackfreed

In research: Stackfreed appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Stackfreed in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Stackfreed is common in secondary-school and first-year university syllabi. It links to neighbouring topics 15th-century inventions, Timekeeping components, so understanding it makes those chapters shorter.
In everyday life: Look for Stackfreed outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Stackfreed” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Stackfreed in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Stackfreed means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Stackfreed out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Stackfreed in simple terms?

Why does Stackfreed matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Stackfreed?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Stackfreed.