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  1. #161
    v76
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    Re: Woke up 3 weeks ago today, my PO no workie...

    Actually, I need to read up a little more on movements, and escapements in particular. I don't have a PhD in kinematics or analytical design related fields ... well in fluid dynamics really (modeling reacting, multiphase flows and also combustion), but have had a fair bit of exposure to those fields. I remember someone else mentioning use of a commercial finite element package like ANSYS or ABAQUS to analyze the mechanism and do a dynamic analysis, that would not be a bad idea at all. Of course, getting the correct dimensions and profiles on the dynamic interacting parts would not be easy since most of that information would be proprietary.

    I indulged in a lot of flailing and hand-waving which was totally unnecessary, in retrospect
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    Re: Woke up 3 weeks ago today, my PO no workie...

    Quote Originally Posted by teeritz View Post
    Watch repairers are not like car mechanics. I have found seven to eight weeks to be pretty standard operating procedure. I tell every customer that it will take 2-3 weeks to get their watch evaluated.
    Just be glad you're not sending in a vintage IWC for restoration. 'Cos 39 weeks is a damn sight longer than 7.
    Does Omega have specific repair centers or are they Swatch Group repair centers? I assumed the latter, which is why I was surprised by the turn-around time.

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    Re: Woke up 3 weeks ago today, my PO no workie...

    Quote Originally Posted by v76 View Post
    Actually, I need to read up a little more on movements, and escapements in particular. I don't have a PhD in kinematics or analytical design related fields ... well in fluid dynamics really (modeling reacting, multiphase flows and also combustion), but have had a fair bit of exposure to those fields. I remember someone else mentioning use of a commercial finite element package like ANSYS or ABAQUS to analyze the mechanism and do a dynamic analysis, that would not be a bad idea at all. Of course, getting the correct dimensions and profiles on the dynamic interacting parts would not be easy since most of that information would be proprietary.

    I indulged in a lot of flailing and hand-waving which was totally unnecessary, in retrospect
    I was actually thinking about dynamic forces with respect to Matt's oil migration theory the other day, but after a very rough back-of-an-envelope calculation realised that dynamic effects caused by the movement of the mechanism itself should have little influence on lubricant distribution or migration.

    If I estimate the escape wheel to be 5.0mm in diameter and rotating at the rate equivalent to 3.5 teeth per second, this equates to an average rotational speed of 2.75 rad/s (it has 8 teeth). If the escape wheel would rotate at this constant rate, a molecule of Moebius D5 on the tip of a tooth would experience a centripetal acceleration of 0.02m/s^2. Now this is of course a drastic over simplication, as the escape wheel is repeatedly starting and stopping, and not rotating at a constant rate. The molecule of Moebius therefore experiences a jerk and much higher acceleration. However considering that 0.02m/s^2 is several orders of magnitude smaller than acceleration due to gravity, this leads me to conclude that the effect of the rotation of the escape wheel is not such that the lubricant will be redistributed. After all, the viscous shear forces within the oil also need to be overcome, and as the escape wheel rotates gravity alone would have a higher tendencey to re-distribute oil than the dynamic motion alone. In short, the escape wheel is too small and rotating too slowly to cause the lubricant to move around.

    Anything more than this rough calculation would require me to reach for textbooks I haven't touched for many years and it's also a while since I did anything in ANSYS...

    The idea proposed by Matt of small channels on the surface of components (as a result of by imperfections, contaminants, burr) causing lubricant to migrate through capillary action (think about WD40 creeping into grooves and holes when it is applied to a machined component) is rather plausible.

    So, let's see if I can't turn this into the most boring thread on the forum
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    Re: Woke up 3 weeks ago today, my PO no workie...

    I indulged in a lot of flailing and hand-waving which was totally unnecessary, in retrospect
    In this situation, we are all doing that. Yours was clever flailing and hand waving and was interesting to read, which is a nice change. In this area, at least, I have just had a few years more practice!
    Luck happens when preparation meets opportunity. Seneca

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    Re: Woke up 3 weeks ago today, my PO no workie...

    I was actually thinking about dynamic forces with respect to Matt's oil migration theory the other day, but after a very rough back-of-an-envelope calculation realised that dynamic effects caused by the movement of the mechanism itself should have little influence on lubricant distribution or migration.

    If I estimate the escape wheel to be 5.0mm in diameter and rotating at the rate equivalent to 3.5 teeth per second, this equates to an average rotational speed of 2.75 rad/s (it has 8 teeth). Now this is of course a drastic over simplication, as the escape wheel is repeatedly starting and stopping, and not rotating at a constant rate. The molecule of Moebius therefore experiences a jerk and much higher acceleration. However considering that 0.02m/s^2 is several orders of magnitude smaller than acceleration due to gravity, this leads me to conclude that the effect of the rotation of the escape wheel is not such that the lubricant will be redistributed. After all, the viscous shear forces within the oil also need to be overcome, and as the escape wheel rotates gravity alone would have a higher tendencey to re-distribute oil than the dynamic motion alone. In short, the escape wheel is too small and rotating too slowly to cause the lubricant to move around.

    Anything more than this rough calculation would require me to reach for textbooks I haven't touched for many years and it's also a while since I did anything in ANSYS...

    The idea proposed by Matt of small channels on the surface of components (as a result of by imperfections, contaminants, burr) causing lubricant to migrate through capillary action (think about WD40 creeping into grooves and holes when it is applied to a machined component) is rather plausible.

    So, let's see if I can't turn this into the most boring thread on the forum
    Nothing, and I mean nothing, would give me more pleasure. I scent expertise... It's an interesting problem and, frankly, it never hurts to brush up on your basics... Keep this up and you might well tempt this Phd in tribology to weigh in and that could get genuinely exciting.
    If the escape wheel would rotate at this constant rate, a molecule of Moebius D5 on the tip of a tooth would experience a centripetal acceleration of 0.02m/s^2.
    While I feel sure that the viscosity is never going to be seriously challenged, remember that the pinion spends a fair amount of time just standing still and that the oil is rolled through by the pallet (in fact on the pinion, you only apply two drops and rely on the pinion to 'paint' the D5 onto the remaining teeth.

    The real question is what is the oil actually doing when it gets where it shouldn't? I have never quite been able to work out why it should have such a drastic effect there. (if it does). Elsewhere, I could understand...
    Luck happens when preparation meets opportunity. Seneca

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    Re: Woke up 3 weeks ago today, my PO no workie...

    Quote Originally Posted by M4tt View Post
    Nothing, and I mean nothing, would give me more pleasure. I scent expertise... It's an interesting problem and, frankly, it never hurts to brush up on your basics... Keep this up and you might well tempt this Phd in tribology to weigh in and that could get genuinely exciting.


    While I feel sure that the viscosity is never going to be seriously challenged, remember that the pinion spends a fair amount of time just standing still and that the oil is rolled through by the pallet (in fact on the pinion, you only apply two drops and rely on the pinion to 'paint' the D5 onto the remaining teeth.

    The real question is what is the oil actually doing when it gets where it shouldn't? I have never quite been able to work out why it should have such a drastic effect there. (if it does). Elsewhere, I could understand...
    If this was a problem with the machinery I deal with as part of my work, it would be crying out for a FMECA (Failure Modes Effects and Criticality Analysis) to be done, or indeed to have been done in the first place.

    FMECA is a really nice approach ideally applied in the early design stages of a new system, machine, product or otherwise to systematically assess the function of each sub-system or component, determine the corresponding modes by which the sub-system can fail to perform that function and the effect (with corresponding severity) this can have on the overall system function. Seems to me that applying this to a cal 2500 would be a pretty interesting exercise.

    In fact, if I had been so interested in watches back when I was studying, I might have looking into this area as a thesis topic instead of just choosing one from the list that the lecturers handed out.

    [Anyone interested in knowing what a FMECA is should read this: Failure mode, effects, and criticality analysis - Wikipedia, the free encyclopedia. There is actually a very weak Omega connection, as the FMECA process was developed by the US military and applied by NASA during the space race in the 1960s]
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    v76
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    Re: Woke up 3 weeks ago today, my PO no workie...

    That's a nice little back-of-the-envelope estimate ChronoScot, and a rough one is better than none at all! To pull this thread further downhill, I found this little paper on the microscopic theory of Amonton's laws of static friction* ...

    Interesting ... in reading up on the Moebius (9415?) used for pallet stones, I came across the property in which their viscosity decreases with applied shear rate ... a pseudoplastic fluid. I suppose the D5 is similar. Hmm ... it is also labeled as thixotropic elsewhere, I'm not sure that is correct ... that is decrease in viscosity over time (usually with agitation or stress).

    Just wondering idly ... if the impulse is small in the case of the co-axial (just enough to maintain motion, as in the swing analogy Matt had given), is it possible that the shear rate on the oil (co-axial case) is not high enough to reduce viscosity (to prevent "sticking") to sustain continuous motion? The sliding contact of the pallet stones in the Swiss lever would reduce the viscosity sufficiently I suppose for low parasitic torque effects. But, I suppose Omega would have accounted for this and used the appropriate grade/type oil ... gah, more hand-waving from me!

    *The scales involved in the two escapements throws my lubricant and contact theory out of the window, though I suspect the capillary action effect might still have some role ...
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  8. #168
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    Re: Woke up 3 weeks ago today, my PO no workie...

    I was a reliability engineer (a few years back), and our team used to sit with the design team to trash out an FMEA for NPI (new product initiation) projects for a LARGE energy company. Those used to be fun!

    Quote Originally Posted by ChronoScot View Post
    If this was a problem with the machinery I deal with as part of my work, it would be crying out for a FMECA (Failure Modes Effects and Criticality Analysis) to be done, or indeed to have been done in the first place.

    FMECA is a really nice approach ideally applied in the early design stages of a new system, machine, product or otherwise to systematically assess the function of each sub-system or component, determine the corresponding modes by which the sub-system can fail to perform that function and the effect (with corresponding severity) this can have on the overall system function. Seems to me that applying this to a cal 2500 would be a pretty interesting exercise.

    In fact, if I had been so interested in watches back when I was studying, I might have looking into this area as a thesis topic instead of just choosing one from the list that the lecturers handed out.

    [Anyone interested in knowing what a FMECA is should read this: Failure mode, effects, and criticality analysis - Wikipedia, the free encyclopedia. There is actually a very weak Omega connection, as the FMECA process was developed by the US military and applied by NASA during the space race in the 1960s]
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    A few of this and some of the other ...


    "I worked my way up from nothing to a state of extreme poverty" - Groucho Marx

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    Re: Woke up 3 weeks ago today, my PO no workie...

    My head hurts.
    Bill

    Desire peace? Prepare for war.

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    Re: Woke up 3 weeks ago today, my PO no workie...

    [QUOTE]
    Quote Originally Posted by v76 View Post
    That's a nice little back-of-the-envelope estimate ChronoScot, and a rough one is better than none at all! To pull this thread further downhill, I found this little paper on the microscopic theory of Amonton's laws of static friction ...
    I'm really not at all clear as to how or why this paper would be relevant. I'd be delighted if you could explain.

    Interesting ... in reading up on the Moebius (9415?) used for pallet stones, I came across the property in which their viscosity decreases with applied shear rate ... a pseudoplastic fluid. I suppose the D5 is similar. Hmm ... it is also labeled as thixotropic elsewhere, I'm not sure that is correct ... that is decrease in viscosity over time (usually with agitation or stress).
    Well apart from the fact that D5 is an oil and 9415 is a grease, I'm sure they are almost identical. D5 is not thixotropic, 9415, being a grease, certainly is.

    I think it might be helpful if you considered the difference between psuedoplastic and thixotropic behaviour. They are not the same.

    There's a point at which handwaving starts to obfuscate. I enjoy the smells of the country as much as the next man, but...
    Luck happens when preparation meets opportunity. Seneca

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