Making a main spring for a clock from scratch
When you need a new mainspring in a movement its normally possible to source a unit from a range of sizes and variations. There are a number of online retailers who supply enthusiasts and trade customers like me.
Every now and again you come accross a spring that cant be sourced. In these cases I have to manufacture the spring from spring strip. This is quite a process and I thought I would share it with you.
Before I continue I feel compelled to say that this is not something you should attempt yourself. Its dangerous when a spring uncoils uncontrolled and you are essentailly dealing with a high speed out of control carbon blade. So dont do it.
My method is very old school because I enjoy setting myself the challenges of the original craftsmen. It produces a much more authenic product and means that I really get to know my components very well. This allows me to predict and tailor how they will perform when installed. And its great fun high kudos clockery of course.
Heres a quick picture journal of one I did today.
This is the basic raw material. In this instance is 145cm length, 2cm height, and .5mm thickness suitable for a 45mm barrel diameter. Theres a calculation you have to do I wont bore you with.
The next shot shows the end holes being drilled. The spring wire is so carbon toughened that you cant drill it without first heating the area to be drilled red hot. This reduces the stresses in the metal, burns the carbon out, and makes it closer to mild steel the more you heat and slowly cool. Drilling still requires a cobalt bit in my experience, or HSS if your on a budget. I normally use cobalt because they are stiffer and hold their position well. HSS tend to skate a bit on hard surfaces and are unusable on a hand drill. My drill is a bench mounted unit which is an excellent investment as a general tool anyway. The bit bellow is HSS simply because cobalts of that guage are quite pricey. HSS is better for larger bits!.
Compressing the spring requires a modern spring winder (boring) or a wooden jig with a central metal core for the winding. The jig needs to be braced with wire before any pressure is applied. Once its tight all round then the spring is wound. The picture above shows the wound spring ready for fixing with a wire retainer.
The end result is the bound and coiled spring ready for insertion into the barrel.
Once the spring is pressed into the barrel its ready to fit the arbor.
I always cut a deeper fastening point on the arbor for good measure and to ensure it catches the spring firmly if the clock is ever reverse wound (which disengages the arbor so dont do it).
Thats a quick overview of how its done on a bepoke. If its a stock spring you can see which bits I dont have to do although the majority of the work on a spring change is getting the entire movment disassembled as the spring is really deep in the heart of the mechanics.
How to tell if your clock spring is broken
If you think you have a broken mainspring and would like me to replace please give me a call. You can tell your mainspring is broken by turning the key – if it meets some resistance and winds a bit bofore “slipping” you know you have a break in the middle of your mainspring. If the key turns with no resistance than that is better news as it means the spring may have slipped its arbor and can just be reconnected as opposed to replaced which is about half the cost.