My new to me 145.014 did not came with an antimagnetic cover, tho I have never seen one with a cover I wonder if they were supplied with one? If not, why not and can they use one?

Koen

 

Mark 2's don't come with anti magnetic covers

 

Thank you @robocaspar

Do you know why they don’t have them?

 

Good Question. I believe its due to case redesign for MKII. The mag cover on the original speedmaster was also used to hold the movement in place when the back cover was screwed on. The MKII didn't need this as there is a spacer ring in the MKII case and the movement is held with screw down tabs that attach to that ring.

If you think of it, the mag/dust cover was redundant for the purpose as the case(including back cover) is all iron alloy anyway. The ingress of mag fields is going to be through the front dial if anywhere. I assume they had that covered too...but I don't know exactly what the dial was made from.

 

Not exactly - 300 series stainless steel is austenitic and magnetically permeable...

 

Not knowing what "austentic" means is the context of metallurgy, I did some Googling and I found these articles which would appear contradictory and seem to be from a reasonably reliable sources http://www.bssa.org.uk/topics.php?article=4 and https://www.kimballphysics.com/mult...rmation/magnetic-response-of-stainless-steels

Every day is a learning day

 

You are correct Archer, many steels are but 300 series are not (by comparison)..also due to high nickel content that inhibits magnetic properties.

And Mouse, it is always a matter of degree. Nonmagnetic compared to magnetic. All steels form some level of magnetic barrier, some much better than others, hence the use of the terminology.

So still begs the question originally asked...why doesn't the MKII have the mag cover?
(I assumed it was due to the case being sufficient barrier, but Archer has seeded doubt)

 

Understood, It's all a question of degree, I suppose. The more I find out, the more I realise how little I know.........

http://www.watch-insider.com/reportages/omega-defeats-mechanical-watchs-enemy-no-1/ and http://www.physlink.com/education/askexperts/ae512.cfm

 

It depends what properties you are looking at - many 300 series stainless steels are "non-magnetic" in nature, however cold working can introduce martensite - however this can be transformed by subsequent annealing operations rendering them non-magnetic again.

The key thing in this context is how transparent the steel is to magnetic fields and this may be causing confusion for some here. In a previous life I have used many meters of 304 and 316 stainless for magnetic elevators. These are devices that have stationary permanent magnets in the frame, a stainless steel flat piece that acts as the conveyor bed, and then fabric belting (Habasit usually is what we used) that slid over the steel plate. This caused parts to "stick" to the plate/belt allowing them to be conveyed vertically...if the stainless steel were acting as a magnetic shield, the elevator simply would not work.

There is a reason the inner cover is made of soft iron...

 

Fascinating subject. Would I be right in taking from this that the inner soft iron covers were a way of directing magnetic fields around magnetically vulnerable movements until the gradual introduction of amagnetic movement components made them pretty much redundant?

 

Yes, that's how shielding works when done this way. I can't say with certainty, but my SWAG off the top of my head is that the time when the 861 balance springs were changed from blued steel springs to what I would guess is some Nivarox alloy, happened before the Mk. II was introduced, making the need for such shielding less important.

 

One more reason I love this place, the things you learn!

 

wow all good stuff.

This has most definitely answered my question, thank you archer and all who contributed!

 

if I understand it correctly the cover acts like a sponge instead of a barrier for the magnetic fields?
with all things aside, why would they only have a antimagnetic cover on the back. like @Wryfox mentioned most of the magnetic fields ingress through the dial side.
it would be interesting to see if the hesalite moon watch would be less susceptible for magnetic fields than the sapphire moon watch, if not the cover isn't much more than a fancy movement spacer(I think).

 

And they are not standing still. This is mindboggling

https://www.onscope.com/ipowner/en/owner/958872/ip2.html?ipDb=PTUS

 

I have a sapphire case back on my own vintage Speedmaster, so I used the original case back, the inner cover, a rare earth magnet, and a Gaussmeter to do a little experiment this morning. I placed the rare earth magnet on the back side of the case back and held it there with my thumb. So the case back was between the magnet and the meter, and moved it towards and away from the Gaussmeter a few times in order to find the spot where the meter first started to move, indicating that the magnetic field from the magnet was affecting it. I then did the same with the inner cover (didn't really have to hold the magnet since it sticks to the inner cover) and marked the relative locations on the bench with Post-it notes:



As you can see, the inner cover was able to be closer to the meter than the case back before any magnetism was detected - this indicates the cover is a better shield than the case back against magnetism.

Now I'm sure some people will look at this and say "But the difference is pretty small between the two items, so isn't it true that the stainless does the job almost the same?"

Well yes and no. On the surface it's not a huge difference, but if you take into account the thickness of the material it paints a very different picture, so I used my micrometer to get an idea how thick the case back is, and it's about 1.14 mm thick:



I then measured the thickness of the inner cover, and it's a very slim 0.2 mm thick:



So even though the inner cover is around 1/6th the thickness of the stainless steel case back, it's still more effective at shielding the movement.

Cheers, Al

 

This is possibly getting a bit esoteric, but as a non-physicist, might the experiment show that the shield is redirecting the magnetic field away from the sensors of the Gaussmeter whereas the caseback does not? It was my understanding (from a link I posted above) that this is the mechanism by which such shields operate.

See also http://www.magnetic-shield.com/pdf/how_do_magnetic_shields_work.pdf

 

We've already established that's how these work, so I'm not sure what your question really is.

My post above was addressing the notion that 300 series stainless steel was as effective at shielding, so the inner cover is redundant. It's clearly not...

 

I Don't think they came with them

 

The only point I was making was to clarify that the shielding doesn't block the magnetic field, rather it redirects it around the movement.