The mark of a True Watchmaker- Forming Hairsprings Part 4- Pinning to the stud & final adjustments

This is the fourth and final instalment of my series of posts about forming a hairspring- I will cover pinning the hairspring to the stud, centring the spring between the curb pins, centring the balance staff in shock setting and finally flattening the spring at the stud. These final tasks are extremely important because they influence the function of the spring more so than anything that was done earlier in the process. Although getting things right at each stage certainly helps when you get to this point because its not always possible to correct previous faults.

I left the last instalment at the point of forming the terminal curve, the next step is to pin the hairspring to the stud but before this can be done, the stud needs to be positioned in the balance cock and the screw tightened down to keep it in place. The index pins are then opened to allow the hairspring to be positioned between them. The end of the hairspring can now be inserted into the hole in the stud and a brass tapered pin is used to pin it tight, in the same way that the collet was pinned previously. Any excess pin is trimmed off and the process of adjusting the spring can begin.

How the hairspring is held in the stud…

The hairspring, when at rest, must sit in the centre of the index pins at every point along the terminal curve. The index used on the 6498/6497 has one pin and a regulator key that retains the hairspring vertically, the key must be turned using a screwdriver to close the pins down once the hairspring is placed between them. The index should be able to move from fast to slow without moving the body of the spring. To ensure this is the case, the terminal curve needs to be adjusted to suit the pins. If the correct shape was formed previously there should only be minor adjustment required but sometimes a lot of work is needed.

6497/6498 Regulator (Index Pins)…

In order to check the curve matches the index pins, the index is moved from the stud to the double bend of the terminal curve, the distance between the spring and the pin is observed at each point along the way. If it is closer to the pin at one end or even touching it, the body of the spring will be moved off of centre which isn’t good for time keeping. The spring is manipulated at any point where necessary to ensure it stays centred at along the full length of the terminal curve.

Adjusting the centring between the pins…

Centring the hairspring between the pins is one of the most challenging parts of the whole process in my experience. Forming a correctly shaped terminal curve in the first instance makes things easier but even then the adjustments can be problematic. Its key that the spring remains centred between the index pins when a rest in order for it to function correctly.

If the hairspring at rest is centred between the pins (1) its active length extends as far as the stud and this provokes a maximum loss of time, as the balance oscillates and amplitude increases, the hairspring will come into contact with the pins. (2) From this point onwards the more the amplitude increases, the longer the hairspring stays in contact with the pins which (3) gradually reduces the loss. Conclusion- the higher the amplitude, the smaller the loss.




If the hairspring is touching one of the pins when at rest, its active length extends as far as the pin and this will cause a slight slowing (1). As the hairspring oscillates and amplitude increases at a given moment the spring will move away from the pin (2), from this moment on, as amplitude increases the less time the spring spends in contact with the pin which increases the loss of time until it touches the second pin (3). From this point onwards, the more the amplitude increases, the more the loss decreases. Conclusion- the loss increases as amplitude increases until the hairspring contacts the second pin, from which point the loss starts to decrease.




Once the hairspring is centred between the pins, the collet must be centred over the balance pivot jewel hole so that when the hairspring and balance wheel are fitted to the main plate, the body of the hairspring stays centred. This is important because is the spring is off centre, its weight is off centre which will in turn put the spring out of poise and have a negative effect on its performance. In order to centre the collet, the two 45 degree bends must be adjusted, the angle is either increased or decreased to move the collet into position. This inevitably moves the terminal curve slightly so it must be adjusted again to make sure its centred between the index pins. The index is moved as close to the two bends as possible to prevent the terminal curve from being altered too much when the collet is being centred.

Once the spring is adjusted sufficiently, the spring can be removed from the balance cock and refitted to the balance wheel in preparation for being put into the main plate. Once the spring and balance wheel are refitted to the balance cock, the cock is fitted to the main plate and secured with a screw. The stud must now be moved up or down to ensure the coils of the hairspring are completely flat, if the coils are dished up or down the stud must be adjusted accordingly.

In position for the next stage…

The next step is to ensure the hairspring is flat and centred at the stud. The flatness at the stud is checked by observing the spring at the point it leaves the stud, the spring should be perfectly flat when looking directly at it from the front of the balance cock. The flatness can be altered by manipulating the spring using a pair of tweezers. The flatness is adjusted by placing a pair of tweezers above or below the point it leaves the stud and applying some upwards or downwards pressure until it becomes flat. The centring at the stud is checked by observing the hairspring from the side of the balance cock, if the spring sits too high or too low opposite the stud then the centring must be adjusted. The adjustment has to twist the outer coil of the spring at the stud to the left or right ever so slightly to get the hairspring to sit flat. The tips of a pair of tweezers are placed over the top of the hairspring at a slightly out of vertical to the right or left depending on whether the spring is too high or too low, the tips are then pushed together to manipulate the spring in the desired direction.

The centring and flatness of the spring can also be easily checked by observing the balance staff pivot in the upper shock setting, when the jewel/chaton are removed, if the pivot sits in the centre of the hole and remains perfectly upright then we can say that its well centred and very flat. This can be used as guide when adjusting the spring as any changes that are made become instantly visible which tends to make the process a little easier. Although you sometimes have to remember that it will never be perfect if there were faults at previous stages of forming the spring as they will always remain, thus making it impossible to have the spring perfectly flat or centred.

Once the flatness and centring have been adjusted, the centring of the hairspring between the pins must be checked again because the spring has been altered, if any adjustment is required, the whole process goes full circle back to the beginning as everything that was checked before needs to be checked again and more than likely adjusted again. These adjustments can be a very frustrating especially for the first few weeks because its difficult to figure out where to adjust the spring to correct the fault. We picked up different techniques from the tutors along the way and also discovered some techniques of our own, the result of all of them hopefully creates a perfect hairspring but of course its not quite as simple as that….

One of my finished hairsprings…

And in action…

The whole process from start to finish is full of obstacles to overcome and can be extremely difficult at times but also rather easy on other occasions, I have to say the last couple of months have been very stressful and hairsprings have been the toughest part of the course so far. Thankfully the exam is now out of the way, I made a few errors and corrected a problem that would have meant the spring failing to meet the standard to pass, and I’m glad to say that I passed. My only regret is that one problem with the spring that I hadn’t encountered before lost me a large number of marks and resulted in a good spring becoming an average one. I was a little disappointed as the score wasn’t really a true reflection of the springs I had been making previously but things can happen during exams and I’m still pleased to have passed. The only examinations remaining now are the final exams in July next year after which I will hopefully be a qualified WOSTEP watchmaker!

School has now finished until after the Xmas period so I’m travelling back home this weekend to visit my family and have a well deserved break…

Note- Diagrams are from the WOSTEP Theory of Horology.

Posted in The British School of Watchmaking and tagged , , , , .