Cutout in the mainspring barrel lid

[Klassiker]

This seems like such a basic question, so apologies if it's common knowledge or been asked many times before, but I can't find an answer and It's nagging at me.

What is the purpose of the cut-out at the edge of a mainspring barrel lid? Why does it have the size and shape that it (almost always) does? Here's a typical example:

[jdm]

According to my mentor, it's to remove the barrel lid - I suppose by prying in some way.

But the only time I tried that on a desk clock, both for the mainspring and alarm barrel, it was  clear that would have not worked and just ruined the lid. So I simply pressed on the arbor and removed the lid without any problem.

Another possibility is that it's for lubrication?

[rodabod]

In earlier days, it was often used to help orientate the barrel lid in the same location as parts were hand-finished. But yes, it allows you to pry the cap off. Some barrels are less suitable for pressing the barrel arbor to push the cap off. But that’s still my preferred method. 

[JohnR725]

On 12/6/2020 at 7:38 AM, jdm said:

According to my mentor, it's to remove the barrel lid - I suppose by prying in some way.

one of the things puzzling me with this question is I had seen within the last year explaining what the notch was for. So looking at the usual books there is no mention? But I looked in one more source that's the Chicago school of watchmaking you can get the PDFs off of eBay. Sure enough in the mainspring barrel section it says the notch is for prying with a screwdriver. That's not normally the method I would use and any time I tried its definitely not the method I recommend.

On 12/6/2020 at 7:38 AM, jdm said:

Another possibility is that it's for lubrication?

I'm the skip over how I know this one perhaps it's really for the opposite? If you get carried away with your mainspring lubrication it leaks out the hole and gets all over everyplace.

[oldhippy]

 Its there for you to remove the cap by inserting a screwdriver.

[jdm]

3 hours ago, JohnR725 said:

But I looked in one more source that's the Chicago school of watchmaking you can get the PDFs off of eBay. Sure enough in the mainspring barrel section it says the notch is for prying with a screwdriver

I would understand if the recommendation was to use an L shaped hook and pull up vertically. But with prying the force is off the axis, makes the lid bind and the most immediate result is dings and frustration.

Quote

That's not normally the method I would use and any time I tried its definitely not the method I recommend.

Exactly.

[nickelsilver]

I'm with most above, for clock barrels I'll give a quick smack with a plastic faced hammer on the arbor to pop the cap. Most of the time on watches similar, pressing down on the arbor to pop the cap. But in some cases you really need the slot; on a lot of older high end calibers like JLC 122 you have a situation where the ratchet wheel is part of the barrel arbor, with the hook threaded on to the ratchet. In these cases the slot is usually particularly well designed and a properly fitting screwdriver will get it off with no damage.

[praezis]

I am with oldhippy's method.

But now I know where all the bowl shaped caps come from 

Frank

[Klassiker]

On 12/6/2020 at 10:02 PM, rodabod said:

In earlier days, it was often used to help orientate the barrel lid in the same location as parts were hand-finished.

But there would need to be a corresponding mark on the housing for this to work. And why a cut-out and not just a surface mark? Not disputing a watchmaker could use it for orientation, but is that why it is there?

The concensus seems to be that the designers put it in so that watchmakers can lever the lid off, but watchmakers will in most cases only use it like that as a last resort. Not really necessary, but not causing any problems, so no need to change it. Is that a fair summary? Apart from special cases like the one described by Nickelsilver, does anyone prefer to lever the lid off, rather than pressing on the arbor?

[JohnR725]

6 hours ago, nickelsilver said:

for clock barrels I'll give a quick smack with a plastic faced hammer on the arbor to pop the cap. Most of the time on watches similar, pressing down on the arbor to pop the cap

 

as usual problems in the horological discussions can occur like here.

Whacking with a hammer seems a bit harsh like very bad things would occur except it's how I take my lids off the barrels of the watches that I work on. There typically American pocket watch lids. I've try because there's a notch and I know what the notch is for I've tried I usually can't get the screwdriver underneath I usually scratch the edge of the barrel and usually the lid does not come. Somewhere in my life somebody showed me somewhere whacking with a hammer works really well.

Okay everyone take a deep breath the world did not come to the end because I whacked with a hammer. As far as I can tell I've never had distortion of the lid because these are like small clocks in a way they're very thick and it's a very sudden fast impact.

If it's something modern I usually put it in the palm of my hand use the backside of the tweezers and just push the arbor and pop the lid off. That method corresponds sort of like the image I attached of how the Swiss perceive you should remove the modern lid. Then they also recommend putting it back together without the mainspring and verifying that the lid is  flat and not distorted.

[rodabod]

42 minutes ago, Klassiker said:

But there would need to be a corresponding mark on the housing for this to work.

Yes, there will occasionally be a corresponding mark on the barrel edge. If not, then there may be an additional mark on the barrel cap. But it’s not the original reason for the cutout, obviously. 

[nickelsilver]

8 minutes ago, rodabod said:

Yes, there will occasionally be a corresponding mark on the barrel edge. If not, then there may be an additional mark on the barrel cap. But it’s not the original reason for the cutout, obviously. 

Following up on john and rod- rod, I usually line up any notch with the hooking point on the barrel as a matter of course. If there's anything to line up that's it.

 

John, I think we agree. A quick tap is not the same as a hydraulic press. To smack an arbor to release the lid is ok. There are a lot of calculations on this but a quick tap vs a prolonged push just aren't the same in mechanics. My first job in Switzerland, when my future boss learned I'd worked in automotive, was way reassured on his hire- (he was already happy with the hands I'd filed).

This is something I've tried to drill into the very talented heads I've come across in the last couple of decades. Smart kids. Explain building up a -smack- instantaneous calendar, vs an automatic winding system. Same stuff I drill in my daughter's head when her mom freaks that there's sulfuric acid, acetone, cyanide, and ammonia in my workshop. She quotes to me now even when we talk about sugar  "it's all about dose,dad".

 

Try doing the math on an uppercut punch, then see if you can reverse it over 5 seconds. The smack is everything. I have numerous presses I use where regular watchmakers would use a staking tool. But when I need a smack! it's all hammer.

This is applicable all over, but suffice to say I've yet to disort a barrel lid from a smack .

 

 

[Klassiker]

Many thanks to all of you for the informed discussion! It's not everywhere you can get people to take such a trivial point of interest so seriously! I love this forum!

By the way, I can also vouch for the difference between a smack and a static load. I have some experience in crash-testing, and the peak forces involved are enormous. The only reason you and the car are not crushed completely flat is that the forces only apply for a few milliseconds. If you're lucky, the transfer of energy to your organs is relatively low, and they just wobble around a bit inside you. I've always used the fingernails-on-the-teeth method illustrated above up to now, but maybe I'll get the hammer out next time.

[Xilikon]

There is one case I noticed that and it is on a russian Vostok 2234SU movement. The barrel have a notch on the lid and barrel and it's to fit the T shaped mainspring end to lock it. I also push it on the anvil to pop it off instead of prying with the screwdriver anyway.

[JohnC]

On 12/8/2020 at 5:56 PM, JohnR725 said:

I've try because there's a notch and I know what the notch is for I've tried I usually can't get the screwdriver underneath I usually scratch the edge of the barrel and usually the lid does not come.

Having done this very thing just now I swear I will never put a screwdriver near a barrel notch again. It's tough because big pocket watch lids don't want to come off easily like wristwatch barrels by just pushing on the arbor. In future I may use brass tweezers, as I can fit them further inside the barrel. But never a screwdriver. Never, never a screwdriver.

[LittleWatchShop]

On 12/10/2020 at 2:17 PM, Xilikon said:

The barrel have a notch on the lid and barrel and it's to fit the T shaped mainspring end

I just ran across this on a Waltham 6-0-D.  In this case, the barrel had two notches.  One is moon shaped and the other fits over the T.

[LittleWatchShop]

19 hours ago, LittleWatchShop said:

I just ran across this on a Waltham 6-0-D

Here it is