Negative pressure tester DIY

Discussion in 'Horological Tools' started by karlmansson, Jun 4, 2019.

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  1. karlmansson

    karlmansson Registered User

    Apr 20, 2013
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    Hello!

    I just posted this video of my shop built pressure tester on YouTube. Thought it might be of interest to some of you.



    Best regards
    Karl
     
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  2. glenhead

    glenhead Registered User
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    Dang, Karl, that's the smartest gizmo I've seen someone put together in a long time! The worst that can happen is that you pop the crystal, as opposed to having the crystal implode and break things and fill the watch with water.

    A question I've always wondered about, since it sounds like you have experience with a store-bought negative-pressure tester. If you're not sure you can trust the integrity of the watch, would you leave the battery out of a quartz watch, test it, install the battery if it passes, and test it again to make sure you didn't miss with the gasket or something? In other words, can one trust a watch battery in a vacuum?

    Nice build, sir.

    Glen
     
  3. David S

    David S Registered User
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    I echo Glen's comment re being a clever set up. However regarding the battery, as long as the crystal doesn't pop or some other leakage, then there still should be +ve pressure in the case. No? At least more than a vacuum.

    David
     
  4. novicetimekeeper

    novicetimekeeper Registered User
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    It is very clever, but can you explain why you need it to me? I've climbed mountains so I have been at reduced pressure, but not enough to damage my watch I'm sure.

    Isn't an increase in pressure more likely? After all you can only get down to near zero, but you can easily get to several bar positive pressure.
     
  5. MartinM

    MartinM Registered User

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    Another more common approach is to do this in a vacuum with the device submerged in water and pull enough vacuum to not start cavitation (boiling) of the water and look for bubbles coming from the device. The downside of that approach is that you may introduce water to the internals.
    Doing this using positive pressure would almost necessitate holding the item under pressure and submerged in a liquid and then inspecting the opened device to see if any liquid had entered. But, then you need to be sure you've sealed it all up correctly, again.
     
  6. karlmansson

    karlmansson Registered User

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    Thank you! Much like the engraving setup on my youtube channel, I've never laid my hands on a commercial version of the tool. I've looked at images, read the manual and understood the concept of it. That was enough to build something like it.

    I think I explained it pretty well in the video but I'll go again: The idea is not to test the watch for how it will handle negative pressures but to assess the integrity of the seals and gaskets. If the case has a leak, that leak will show up more obviously if the case is exposed to negative pressures as an external, positive pressure will compress the seals and make the case MORE waterproof than it will be at 1 bar. If you want to check a case for waterproofness at a certain pressure, you'll have to build up a positive pressure that matches the rating of the watch, sure. But for everyday use, a negative pressure test can be more appropriate as it will tell you if the watch will handle a rain shower or washing the dishes with splashes. Something that might not be true for a watch tested at 20 bars.

    The method I usually do for wet testing is to expose a watch to a positive pressure for a couple of minutes and then dunk it into water before I release the pressure. Bubbles will then show up at any leak points. The principle is pretty much the same for that test compared to my negative pressure test (there is a higher relative pressure inside the case compared to the surrounding atmosphere at the time of testing) apart from two things: the wet test I just described relies on air getting INTO the case to begin with. This may not be the case for reasons described above. The second aspect is that a wet test performed in this way will show the points of leakage as a stream of bubbles will show. The negative pressure tester only shows that there is a leak, not where it is. Elma makes a paste to rub on any suspect surfaces and that then bubbles up if there is a leak under vacuum.

    Thanks again fellas! Appreciate the comments and kind words.

    Best regards
    Karl
     
  7. doc_fields

    doc_fields Registered User

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    Karl,
    Excellent idea and build! My hat is off to you!.....................doc
     
  8. DeweyC

    DeweyC Registered User
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    Karl,

    Nicely done. I used to have the Elma and I see no reason why your execution is not as effective.

    I am not sure where cavitation comes into this. Cavitation is the result of sudden pressure differentials within a fluid that causes voids that implode within the fluid and cause shock waves. It is usually associated with impellers and propellers although I know some organisms that hunt using this phenomenon.

    Boiling is actually a transition state where a liquid is heated enough to move into its gaseous form. It is about temperature and vapor pressures.

    I am not aware of any vacuum pump that can cause the sudden drop in pressure required and I doubt it is a concern for your design.

    How is the watch design coming?
     
  9. novicetimekeeper

    novicetimekeeper Registered User
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    You can boil water with a vacuum pump, you need to stop the water going through the pump so it takes a special set up. Boiling is a state change but it doesn't necessarily require additional heating. It depends on the liquid. Water will boil and then freeze under vacuum.
     
  10. karlmansson

    karlmansson Registered User

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    Thank you Dewey!

    I'm not sure if your entire response was directed to me, I believe it was MartinM that brought up the cavitation issue. That being said, during a wet test, the increase in size of any small air bubbles that went down with the case into the chamber can be misleading. Since I'm not dealing with water at all in this build I don't have any issues with boiling or even engrossed bubbles.

    Heh, the watch design is in a preparatory state at the moment, sandwiched between work in the ER and tooling up the workshop for manufacturing work. I'm still sanding away on the body filler on my Habegger DLZTE... I have some modification work I'd like to try first, I have a design for a remontoire that I'd like to try and build into a pocket watch and I'm learning about case making as well. Working in sterling silver.

    Best regards
    Karl
     
  11. DeweyC

    DeweyC Registered User
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    Agreed. Vapor pressure is the key to boiling. I did not go further than that because boiling and cavitation are two different things entirely.
     
  12. DeweyC

    DeweyC Registered User
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    You are just like a cardiologist with whom I wrote a paper or two. He had the usual degrees and credentials, had his research program as well as clinical practice, had an MPH and PHD, gave piano recitals and was also an amateur archeologist. Me, I have trouble doing trail work and watch work.

    I look forward to your watch; especially your aesthetic choices. Learning about cases too!! You go guy!
     
  13. novicetimekeeper

    novicetimekeeper Registered User
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    It's perhaps a bit lax, but cavitation is a localised change of state. As you say, cavitation results in the sudden collapse of the areas of low pressure.
     
  14. DeweyC

    DeweyC Registered User
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    I love it. Precision in watches and precision in language. Great discussion!
     
  15. karlmansson

    karlmansson Registered User

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    Well, my CV isn't quite that heavy yet. Although I did study music before starting medschool. Something true for quite a few of my colleagues for some reason.

    I did some experiments a while back with casting remakes of worn out cases in sterling silver. I refined the process some, maybe I shouldmake a post of that, if someones interested.

    I have couple ideas in mind. For one thing, the county where I was born and raised in Sweden has the finest black granite in the world (Duvhult diabase). I've had in mind to make a stone dial for a pocket watch. I happen to know a guy (also a doc, surprise!) who has been doing stone cutting and lapidary work for a big part of his life. He's been helpful in working out the pitfalls of grinding something that fragile into something as thin as a watch dial. The benefit of making my own case is that I get free reign over how much clearance I can create!

    Then there's also the Swedish watchmaking heritage to consider. There used to be a very fine maker of pocket watches in the lathe 1800s in Sweden, in Svängsta, called Halda. As far as I know one of the very few to actually have manufactured watches in full on Swedish ground. It would be nice to include something inspired by their watches in my design. I think my watch will somewhat reseble traditional, English watchmaking but, as with many Swedish things, a bit more sombre and understated :).

    Glad we got that sorted out :). Did my explanation of how my tester works, and the function it fills make sense?

    Regards
    Karl
     
  16. novicetimekeeper

    novicetimekeeper Registered User
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    Yes thanks, I don't have the sound on my computer on so I missed the original explanation.
     
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  17. MartinM

    MartinM Registered User

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    Sorry for the confusion. I was unaware that the boiling in a liquid due to lowered pressure had to be localized to be "cavitation". Live and learn.
     
  18. MartinM

    MartinM Registered User

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    Would it be feasible to create a blank for the dial that's the correct diameter and excessively thick with one face of the 'coin' polished and then superglue it to another, larger slab of granite already in the machine and freshly surfaced/polished?
    Heat, applied very slowly might be able to free the finished dial from the slab.
     
  19. karlmansson

    karlmansson Registered User

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    No, worries! I always thought cavitation was the collapse of the bubbles once the pressure gradient dropped.

    It might work. My plan of attack is to grind one side ofthe disc flat with a rather coarse grit, and then to glue the piece to a copper backing plate. Alternatively an invar disc. Diabase has an incredibly low coefficient of thermal expansion. But then again, I think epoxy does not...

    Then I'll make a jig for drilling the necessary holes in the dial while it's thick and has ample support from the back to prevent blowouts. The metal disc and it's dial feet will give me something to hold on to as well. Then I'll start thinning the stone down, either on a lapidary grinder or in the lathe with diamond tooling. I'm planning to make a sub-second recess with a coarser finish than the rest of the dial, so that will have to be done on the lathe. Same goes for all other contrasting features. Diabase can be polished to an extremely smooth and reflective surface and the transition between smooth and rough can be made pretty dramatic.

    Regards
    Karl
     
  20. Chris Radek

    Chris Radek Registered User
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    Karl, I've drilled a lot of holes in glass using my mill's helical interpolation, just using regular cheap diamond burrs under a good flood of water. I figure drilling in a helix (with radius of motion less than the tool's radius) lets water get down to the bottom of the hole, and lets the grit get out. I end up with good holes and very little chipping on the back side. I can imagine doing the same on a lathe, with a live tool not quite concentric to the spindle, with fast live tool speed and slow spindle speed.
     
  21. Dushan Grujich

    Dushan Grujich Registered User

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    G'Day Karl!

    Perhaps You can try and apply petrographic techniques for making microscope slides in order to make thin stone dial for a watch. It is a fact that as early as nineteenth century mineralogists were hand making thin section mineral slides as thin as thirty micrometers, as standard.

    It would be worth while if You would investigate some of the techniques that mineralogists use. For dial making instead of microscope slides one can go as high as five hundred micrometers in thickness without any problem, of course subject to the quality of the mineral used. BTW, Canada balsam can be used as a mountant i.e. a glue.

    If You want, I can provide some written material on how such a task is usually performed.

    Cheers, Dushan
     
  22. karlmansson

    karlmansson Registered User

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    Please do, Dushan! It would be much appreciated.
     

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