So today I was feeling particularly dexterous and decided to open up the case back of a vintage watch with a small scissor. I usually get a watchmaker to do it but I thought I could do a bit of practice.

Opened up, movement looks clean despite its age and obvious surrounding degradation... and...a screw? fell out.


(P.S if anyone can identify what movement this is?)


I am guessing the screw belongs to the hole above the word 'Swiss', or the hole on the upper most right corner? Would there be any effect on the running of the movement?

Although, the watch is running well and keeping time. Would be interesting to hear the views of people familiar with movements

 

The screw is for retaining the movement, same as the one on the opposite side.

Looks like an AS1130 movement.

 

This would be my guess...but I know very little about these matters.

 

For next time, if you don't have a reliable blade, a thin scalpel/craft blade will do the trick. @Archer would advise that you only use it to prop the caseback up and gently work it around the case, rather than 'levering' it as some people tend to do.

There's no hole above the word 'Swiss' unless you're referring to the one near the click. It would be, as @JimInOz has stated, one of the two retaining screws that holds the movement to the case. This could spell trouble particularly if you notice that the movement moves around in the watch while you're wearing it...

 

I am hoping the movement is still secure, I picked up the watch and moved it and haven't heard any audible creaking yet haha

Just did a google on the movement. Seems like an army watch movement

When I observe the caseback there was a small crack which I guess must be from the frequent openings in the past. So I followed along. To be fair I was very rough and my blade might have stabbed the movement, if that makes sense.

 

Very good JimInOz!
http://www.ranfft.de/cgi-bin/bidfun-db.cgi?10&ranfft&&2uswk&AS_1130

 

Quick. Put it back inside and close up the case!

 

I don't need to consult Dr Ranfft for this one, I've seen enough of them in the fake Seamasters that hit eBay about twice a day.

 

I stabbed myself in the hand about 11 years ago, no screws dropped out, but a brick might have....

 

That is not a dog screw, no matter how old you are...

 

Uhhh okay...but it's still not a dog screw. Here is what a dog screw looks like:



From Merriam-Webster:

Definition of dog screw​

​

: a screw with an eccentric head or with one side of its head removed that is used for attaching a watch in a case ​

The screws above are just regular case screws.

Cheers, Al​

 

@Archer Any idea why the head would have been eccentric – is this another way of saying proprietary? This would make sense, a screw that was difficult to turn without tools of an authorized watchmaker. And what is the functional purpose of a half-head screw? What's the deal with these? Also, why do I care???
​

100% correct.

 

https://omegaforums.net/threads/a-warning-you-morons-and-do-it-yourselfers.37759/

 

Well... Bill... I never suggested you go argue with him...

But to call all case screws dog screws is like calling all 30T2's "RG" to put it into perspective.

That I can't answer, but they are a horrible design really. Over time, in particular on softer case materials, they will chew up the edge of the case. Thankfully they have pretty much gone out of style now.​

Cheers, Al

 

Thanks, Bill. Makes sense. I was thinking more along the lines of clearance for some portion of the caseback, but nope.

 

Not sure I understand how dog screws are fundamentally different from the more common/modern (runaway) screw first depicted by the OP. Aside from not needing to be fully removed from the movement. But I think I've got bigger problems, frankly, in my understanding of how a caseback (or dog) screw actually secures the movement in a watch case.

Back to the OP's original image, I can see how these screws prevent the movement from falling forward toward the crystal, but it's not 100% clear to me how (or if) it prevents the movement from being pulled from the caseback side once the caseback is off.

Are case screws helping to wedge the movement at the sides of the case as they are tightened? Are they very slightly off-angle so that they eventually make contact at the edge of the movement with the inside of the case? So many mysteries.