Stiction

Discussion in 'Armory - Q&A' started by jjefferies, Apr 24, 2019.

  1. jjefferies

    jjefferies Podium

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    Technically speaking, is crunchiness in epee tips a function of stiction or are there other factors? And how would you describe those other factors?
     
  2. DangerMouse

    DangerMouse Podium

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    I usually find that it is a function of burs in the screw slots that provide a mechanical barrier.
     
  3. K O'N

    K O'N Podium

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    Burrs in the screw slot as DM said, or just dirty as hell, or a bent contact spring grinding on a German wire's volcano tip.

    In club blades it's often that the tip is dirty. A quick fix is to spray a bit of contact cleaner into the tips and hit your own foot a dozen times or so. Gets most of the dirt out and provides a bit of lube. Not an appropriate technique for highly maintained personal epees, but if you have twenty club blades to keep working it's a godsend.
     
  4. neevel

    neevel Armorer

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    Dirt or dinged screw slots. Take care of the first by cleaning with alcohol or contact cleaner and a cotton swab, use a needle file to smooth out the second (if there are enough, or very large burs, rewiring with a new barrel may be the only proper solution). With use, you can also start to get scratches on the inside of the barrel that can increase friction; if you want to take the time, polishing the interior of the barrel will progressively finer grit sandpaper (start with a fine grit and go finer from there) wrapped around an expanding mandrel can mitigate that.

    The problem with any lubricant is that, unlike a car engine where the oil is kept protected from most outside contamination behind the fuel and air filters and continuously circulated through the oil filter, an epee point is open to the environment and has no filter system. That means that any dirt and grit that get into the point will tend to be retained by the lubricant instead of falling out, and so the point in a short time will be stickier than it would be without the lubricant.
     
  5. posineg

    posineg DE Bracket

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    Not sure how common this is but I have had plating from the springs(?) cause grindage/contact issues as well.
     
  6. jjefferies

    jjefferies Podium

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    Perhaps I should rephrase the question. First of all stiction is the static friction needed to be overcome, https://en.wikipedia.org/wiki/Stiction. All/most of the causes listed above probably come under the broad heading of stiction. But I've noticed that even after stiction is overcome there is a continued crunchiness (non-technical term) that as DangerMouse suggests could be burrs which continue to hinder movement of the tip. I'm trying to understand these as separate from those which might more properly be call stiction.

    And then I'd like to categorize tips in light of their being subject to such factors. One thought is do tip screws which recess deep into the slots reduce both stiction and continued crunchiness?
     
  7. brtech

    brtech Podium

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    Not a mech-E, but in my world, a rough slot doesn't count as stiction. Something like an adhesive bond created by lubricant gone awry would be stiction. But anyway, I classify getting rid of crunchiness into:
    1. Slots
    2. Roundness
    3. Surface roughness
    4. Tolerances/Mismatched parts
    5. Spring issues
    6. Contact issues
    Once I address the slot issues, I will pop a new point in and see what it feels like. If I get a significant improvement, I will spend some time trying to figure out if I can make the original tip work, but not much time.

    If a replacement tip doesn't improve it, I usually start with the contacts. If they are level, and the cup is in good condition (visual), I will usually try a quick touchup on the inside barrel roughness. If that doesn't work, I will slide in the mandrel and see how round the barrel is. If I've gotten that far, and with a new tip, it's still crunchy, I have a choice: new barrel + rewire or more time first with the mandrel and then polishing.

    But I'm usually doing this for a team, and there, time is more of an issue than money. I need to get the weapon in top shape NOW, and replacing a tip, even with the time to get the shim set, is often much much faster than figuring out what the problem with the old tip was. If I'm strip side, I'll futz with slots more than if I'm back in my room or armory. I'd really rather replace the barrel than use a file for any dings I can see, but rewire takes lots of time. For slot roughness I can't see, the file usually works well, and I'll replace screws in a heartbeat.
     
  8. brtech

    brtech Podium

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    It occurred to me that I forgot two things in that description, probably because it's already "autopilot" for most of us. The very first thing you do is clean the barrel, and if necessary, the tip. I pay particular attention to the tip if the barrel was pretty dirty. I make sure to get any gunk off the underside of the top of the tip, where it contacts the barrel. I often find I have to scrape some off with a tip screwdriver. Since I have the screws out at that point, I can test the tip independent of slot issues. The other thing is, of course, look at the contact spring and make sure it's straight up and down. Again, as a team armorer, I'm gonna rip a contact spring that isn't looking perfect off and replace it. I don't want to just reset it, because if it was bent, it's gonna bend again soon if I try and straighten it instead of replacing it.
     
  9. jkormann

    jkormann Podium

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    Slight thread drift -- what causes an epee contact spring to bend sideways?
     
  10. brtech

    brtech Podium

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    In my experience, one of two primary causes: 1) It wasn't thread onto the screw well, or it slipped off a part of the thread
    2) The cup is damaged and caught the edge of the spring as it went down to the contacts. There are some oddball cases, and others where I really can't figure it out, but threading issues is usually the problem in my experience. It's pretty common. I've never tried to figure out why it happens. I look carefully at a tip that I've replaced a contact spring on to make sure it's wound around the threads correctly, that it's absolutely straight, and the cup is in good shape.
     
  11. neevel

    neevel Armorer

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    There's a third common cause of contact springs bending: someone tried to stretch the spring to shorten the lighting stroke and bent it while doing so.
     

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