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The mark of a True Watchmaker- Forming Hairsprings Part 1- Pinning, Flattening & Centering

The escapement exam was now complete and it was time to move on to the next part of the course, which is probably the hardest part, hairsprings. I was pleased to achieve one of my best scores to date, showing that all my hard work to date is still paying off. Hairsprings are a slight departure from the skills we have learnt so far in the fact that they require a more delicate touch and even greater concentration for longer periods. They can be, and generally are, mentally exhausting and definitely frustrating.

The whole process of forming a hairspring is something any true watchmaker should be able to do, although this skill is generally not necessary today, it gives a level of understanding of the hairspring that is otherwise difficult to obtain. In todays watchmaking industry the majority of these steps are carried out by machines in all but the most exclusive of watch houses. The main reason for this, is time, forming a hairspring is not something that is done quickly and in a world which revolves around the mantra ‘time is money’ its easy to see why machines have taken over.

The whole process of forming a hairspring can be broken down into a number of steps, the sheet we were given has 32! It was decided that we would focus on a few areas at a time gradually working our way through the process from beginning to end. This has always been the part of the course that I feared as hairsprings are a difficult thing to get right and unlike other parts of the movement, anything over than near perfection results in failure. The next 10 weeks until the exam were definitely going to be the most challenging yet.

We started off with the following- a 6498 Hairspring, a Brass Collet and a Tapered Brass Pin…
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Our first task was to form the inner curve of the hairspring and pin it to the collet. The spring needed to be perfectly centred and perfectly flat. Written as words, this process sounds relatively simple but as with most parts of watchmaking in practice it really isn’t! The inner curve of the spring isn’t large enough to allow the collet to sit inside of it so a portion of the spring must be cut away to accommodate the collet. After the removal, a new inner hook must be formed at a 60 degree angle, it can be tricky to form this hook at exactly 60 degrees, many hours of practice is required. Its crucial that the spring remains perfectly flat at this hook, a bend here can make it impossible to flatten the spring once its pinned to the collet.

Hook cut away…
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New hook formed…
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Once the inner hook has been formed, the collet is placed inside the centre coil of the spring and the hook is carefully inserted into the hole in the collet. The position of the collet can be checked at this point and the hook can be adjusted before pinning if necessary. The most important thing to check is that the hook remains flat because its extremely difficult to correct this once its pinned to the collet. The other key thing to check is that the spring is the correct way up, its easy to get this wrong and not realise until its been pinned, flattened and centred, the whole pinning process has to be started again if this happens.

Collet fitted…
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The next task is to pin the hairspring to the collet using a tapered brass pin. The collet has 2 holes on one edge that line up with each other and into them fits both the hairspring and the tapered pin. Once the spring has been entered into the collet, the tapered pin is guided into the hole on the same side and pushed through as far as possible. The pin will ensure the spring is held tight in the collet through a friction fit. The ends of the pin that protrude from either side of the holes in the collet must be trimmed down so that they do not interfere with the hairspring when its vibrating.

Pin entered into the collet…
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Nearly pinned…
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Ready to cut…

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With the hairspring now pinned to the collet, there are a couple of checks that need to be made and any corrections required are made before moving on to the next step. Firstly the collet must sit perfectly in the centre of the hairspring, any corrections are made by altering the curve of the hairspring where it leaves collet. Once the spring is perfectly centred it must be checked for flatness. In order to do this, the spring is placed on a smoothing broach and then slowly rotated to check for any high or low points. The spring must be perfectly flat and parallel to the collet throughout the 360 degrees of rotation. Any corrections are made by manipulating the coils of the spring up or down.

Time to check flatness…
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The hairspring is now ready to be fitted on to a poised balance wheel in preparation of finding the timing point on a luthy tool. The collet is placed on to the top of the balance staff with the chamfered side of the collet facing downwards. The chamfer in the collet allows it to be removed from the staff using a pair of collet removal levers. The balance wheel is then placed on to a staking tool and using a small amount of pressure, the collet is pressed down into position on the balance staff.

Fitting to the balance wheel…
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After completing the forming and pinning process around twenty times things seemed to finally be getting easier. Initially even the first few steps were pretty difficult, I knew hairsprings weren’t going to be a walk in the park but they are even trickier than I had imagined. Practice makes perfect though and with 10 weeks to go until the exam, I’m sure that I’ll be up to more than the required standard by then.

I’ll continue with the next steps in Part 2 of my instalments on hairsprings…

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