Only fools will go… step 3 - The problems start
I now have a movement with installed going train up to the escape wheel and anchor. It seems very strange to me that when the escapement turns the anchor can get in a state where it wobbles back and forth, but doesn’t lock to the sides. A visit to my tutor shows me how this should look; the anchor should lock conclusively to both sides. Not what I am seeing at all. Exact measuring on an optical table shows that I have drilled the placement for the escapement wheel too far from the anchor, a manufacturing error. It is interesting to note that the geometry of the pallets and escape wheel teeth allows a completely blocking position at a certain, too large, distance between escapement wheel and anchor. This seems counter-intuitive, but is born out using paper cutouts of the escapement wheel and anchor enlarged 20 times.
What to do?
I decide not to completely remake the plate and bridges at this point, but to drill out the existing holes, fill with a brass plug and try to aim correctly when drilling this time. Here some pictures of this work.
Plug in place ready to be pressed in. I am using the jewelling press to press this in and keep control.
After turning down the excess on the lathe facing plate, another try at drilling at the correct position.
After this detour things are looking better.
And here it is, the first picture with the balance mounted… and what you can’t see, it is turning. The amplitude is very weak, but it is self-sustaining.
I am ecstatic!
But now, how to get the amplitude up? The possibilities are multitude. My tutor says if the going train is not perfect there is no way it will work. When wound at the barrel the going train should stop only after reversing. I am not seeing that. I put all the parts through the ultrasonic cleaner to be sure that there are no shavings or dust from all the machining work hiding somewhere and causing problems. Reassembly, checking all shakes and oiling improves the going train so that it really does stop only after reversing, but the balance amplitude shows no significant improvement.
I am slow to see it, but my balance is standing at a slight angle. This appears to be causing the hairspring to touch on one edge of the balance bridge. I did try and cause the hairspring to not touch, but that is not the solution and messed up my hairspring some. I see that once messed up a hairspring can cost one days of work.
In the end I realize that the error happened very early on. I first drilled the holes for the incablock using a standard twist drill, not having a better drill near that diameter. Of course the hole ended up slightly triangular. In afterthought I remember that this is just about always the case with such drills. I then brought the hole up to full diameter on the lathe, but with the triangular hole I lost the real center. I should have used a good drill to assure good centering, as I had to enlarge the hole on the lathe anyway. That way I would have not lost the centering. All the other holes I have drilled with the special hard-metal drills that are made for making the holes in printed circuit board production. They cut clean and perfectly. And the marked drill size is the size of the hole it produces, not the size of the drill. They are a joy to use, but do break quite easily. My tutor tells me that for precise watch work even these drills are too long and can wander. Drills for watch work should be more like 5 mm long maximum I am told.
What to do now? I hate to admit it, but for the moment I have removed the steady pins and with the leeway around the screws am able to move the bridge enough to have the balance stand straight. The balance amplitude is better, but still not good. The balance frequency is also strangely off by about 25%. How can that be?
Give me a little time to find a clean(er) solution for positioning the balance bridge and for another visit to my tutor to elucidate some more possible reasons for insufficient amplitude and wrong frequency.
Yes, things are just fine now, the reason for the frequency and amplitude problem totally unexpected, i.e. not something I did terribly wrong. It was actually just a passing remark of my tutor that set me on the right track. He mentioned once that the 2824 had been made both in 4Hz and 3Hz versions with identical wheel placements. I realised that was exactly the amount I was off. For 15 seconds movement of the second hand it was taking 20 seconds. When this finally dawned on me I quickly opened up another movement to extract its balance/hairspring assembly. Placing them side-to-side, there was no apparent difference in the balance except one was nickel and the other glucydur, but the hairsprings were not the same. So I decided to install the new one and see what happens. And what happened was that the timing is right and the balance amplitude is OK, after a little fiddling to get the pallet draw right.
One of the movements that I canabalised for this project must have been a 3Hz movement. Which means that I must also have an escape wheel/seconds wheel pair for 3Hz too. Maybe that was the seconds wheel who's misery I ended by stepping on it while I was trying to find it on the floor. Since then my strategy for finding pieces that have found their way to the floor has changed to first inspecting the places where I want to put my feet.
There is still a pretty big difference in amplitude depending on the position, between 200° and 290°, and I realise that I should be getting over 300°, but I am going to wait to try to find that until I am finished drilling and filing. I still suspect brass chips or dust hanging out around the bearings as my biggest problem. Once that "dreck" has found its way into the oil, however tiny that amount of oil might be, only a real cleaning will help. I think the "clean" way to do this is to have a room for machining, the "dirty room", and a room for assembly, the "clean room". That way one would have a chance to keep things as clean as one should. When, however, everything is happening on the same benchtop you can be as careful as you want. It is still not enough.
And, BTW, I did find a cheat for re-positioning the balance bridge without lots of work. I turned the steady pins slightly conical, the top end remaining the original diameter. The radius at the position on the pin corresponding to the top surface of the plate is down 0.2mm. I then bent the pin 0.2mm in the direction needed. The pin remains stable and at the same time the bridge still sits perfectly flat on the plate and is well positioned. Although the top of the pin is now at a slight angle the difference is so small that it is invisible. It seems to work fine, but please don't tell anyone.
I am now preparing to finish the keyless works to be able to set the time from the crown. This is the part of the movement that I am most worried about. It has the largest portion of my design, the smallest portion from ETA. Then it will be time to make the hands.
Copyright © 2005 Donald W. Corson