DOXA DIVINGSTAR CROWN REPAIR
© Dr. Peter McClean Millar - June 2005
It is your worst nightmare. Brand new watch, worn once and put into the watch box. Several days later you take it out, unscrew the crown, pull it out and it comes away in your hand.
As can be seen the winding stem has broken and came right out from the movement.
I basically had 2 options. I could send the watch back to Doxa for repair or I could ask them to send me the parts and I'd do it myself. I've pulled apart and refurbished enough watches by now that I felt fairly confident on being able to do the repair myself, so I emailed Rick Marei and told him what happened. Rick said he would immediately send me a new crown and stem. "Great", I thought, this gives me an excuse to open one of the new Doxas and see what the decorated movement looked like.
Now, there are a couple of things people should realize before attempting to do this. You need the proper tools - caseback opener, needle files, movement holder and jewelers tweezers are the basic minimum. You should also have some thread locker. You better be confident "playing" with very small and delicate components and before you do anything, remove the bracelet and put several layers of tape over the caseback. The tape will prevent some scratches if the caseback opener slips. Finally, be very careful and take it nice and slow.
Having followed my own advice and removed the caseback, I was able to remove the movement and see what the problem was. This photo shows the remainder of the winding stem still in the movement.
The above photo shows exactly what happened. If you look closely you will see that the winding stem fractured across one of the threads. There is a small lip visible on the piece that inserts into the movement. Now, many of you reading this know that I have a degree in Metallurgy and a PhD in Corrosion Fatigue of High Strength Low Allow Steel, and I was just itching to get down and dirty and do some failure analysis on the piece, but that part of my life is long gone (I'm a Chiropractor now) and don't have access to the necessary tools any more. However, I was able to get a fairly close look at the break and it looks like the thread has been machined through a very small inclusion in the steel. Any machined thread will act as a stress concentration point. Normally the diameter of the stem has the tensile strength to withstand the pull necessary to engage the date and hand movement trains. However, in this case the effective diameter was greatly reduced by the inclusion and the resulting tensile strength of that area was reduced so much that it was only a matter of time before the stem failed by a very low cycle fatigue fracture. Many people will say that quality control should have found this flaw and extensive testing before dispatch should have rulled out this happening, well it is my personal and professional opinion that this failure was just pure bad luck and was a one in a million. I've actually never heard of a winding stem fail like this before. I also don't think it is worth increasing the quality testing for this type of failure as it is so uncommon - I also happen to have an MBA in Quality Management Systems so I know a bit about that as well - yes, I know, I'm a smart ass. Actually my father says I have more degrees than a thermometer and as the count is now 5, he may just be right :-)
Since the watch was in parts I thought it was a great opportunity to get a close shot of the new Divingstar dial. It really is sharp and well printed with nice crisp lettering. The other thing that is noticeable is that the minute hand is actually slightly curved. People had commented on this before but thought that it was because of the dome of the sapphire crystal. In fact it is the hand that is slightly bent.
And here is the movement. The workhorse ETA 2824-2. It is finished with gold lettering on the rotor and says DOXA TWENTY-FIVE 25 JEWELS SWISS MADE. Recently a number of manufacturers have been using plastic spacer rings to hold the movement in place. I'm happy to report that there is no plastic inside the Doxa. The spacer / retaining ring is metal.
The winding crown / stem arrangement is release by pressing a small "button" on the back of the movement. For anyone who ever wants to disassemble their Doxa I have provided the above photo showing the location of that release.
I received the new stem and crown in about 5 days and set about rebuilding the complete winding stem. Now here's were it gets a bit hairy. The actual stem threads are longer than is needed, so it isn't just a matter of threading the stem into the crown. Nope, it has to be measured and cut to the right length. I put the broken pieces together as best I could and measured it against the new one. I then cut the new stem slightly longer than necessary and using a needle file paired it down and removed the burr from the cut. I tested it a few times before locking the thread into place with thread locker.
And there it is. The re assembly was punctuated by coating the stem tube and case seals with silicon grease and tightening down the caseback. Of course I have no way of pressure testing the case, but I'll never dive with this watch and I would honestly doubt that the watertightness has been seriously compromised. Does it invalidate my warranty? Of course, but that is not a concern for me.
So there you have it. It was a fairly easy job to do and actually quite satisfying. To reitterate what I said earlier, I could not blame this failure on Doxa. It was a freak occurence and in fact, I'm happy it happened to me as it gave me the chance to get close and personal with my Divingstar and rather than blame Doxa, I have to compliment them on their speedy replacement of the crown and stem.