Wirebreaks - In the upper head/nozzle
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  1. #1
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    Default Wirebreaks - In the upper head/nozzle

    OK guys, right outta the gate, I ain't in my first rodeo ....

    I am getting inexplicable wire breaks just above the part.
    Approx 1" above so the wire is already past the power contact and is around the diamond guide area.
    The machine is a Makino U3, so by the time the wire enters the contact area, it is already submerged.
    Once it gets past it, the amount of cooling water only increases, and once past the upper diamond, it is fully enveloped by the flush water.

    Machine had a complete disassembly and cleaning approx 200 hours ago.
    When I say disassembly, I mean if it had a screw, it was removed.
    Filter is only on it's 20-th hour, so another 50-60 to go before any concern.
    Water in clean tank is crystal clear so filter is not blown.
    Power contact indexed 3 cutting hours ago.
    Flush condition doesn't matter, but it is a sealed flush top and bottom.
    There is verified power contact coolant water and plenty of it. Checked it with no wire, flush sealed and pumps-on.

    Anyhow, from what I know, when wire breaks above the part it is typically not related to the "gap" condition, rather inadequate cooling of power contact/wire.

    So, with my checks I have exhausted all possible options until I have a chance to rip it apart again sometime during the weekend.
    The only thing I can see is that after only 3 hours of "bandsaw" cutting of 1.5" thick material, there is CONSIDERABLE wear on the upper contact.
    The wear is not your typical narrow gap "abrasion", rather it is much wider ( like 3x wider), looks like it is arced rather than abraded, and the upper side of the contact
    is black with burn marks .....

    Bit stumped

  2. #2
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    I'm not familiar with Makino, but I assume there are upper and lower contacts. If it is breaking above the part, I would look at the lower contacts and/or cables. Think of the wire as a fuse that can only take so much current. If it keeps blowing out above the part and keeps wearing out the top contacts, that could mean the lower is an open circuit.

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    I had something similar when i had to cut a smaller piece from a chunk , but my problem was that part's upper surface was rusty .

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  5. #4
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    Sounds like the upper contact is not secure. What holds it in place? I would triple check it. We have had similar issues and the contact starts eroding its holder which gets ugly fast.

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    On the U series, there is a spring loaded plunger that clamps the carbide to the copper head.
    Yes, it can get some debris in there, so every time I index or just even remove to inspect the contact I clean the carbide AND the cavity with the plunger.
    It is clean....

    But!

    Oddly enough - even though I did not think the lower contact had much to do with the problem - I took out the lower contact and while poking in there
    with a Q-tip, I've fished out a short piece of broken wire that was quite badly eroded.
    The contact was just fine and no signs of false arcing, but the wire was there nonetheless.

    After cleaning, It's been running for 7 hour now, so far no anomaly ....

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  8. #6
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    OK, returning to this thread to give a final result!

    Let's start by saying that my initial Eureka moment was nothing more than a tiny little straw to grab onto.

    But! I have found the root cause and the method of fix to the problem without any doubt!

    Issue: Wire breaks at the upper power contact.

    Cause: Reduced "cooling" water going to the upper power contact.

    Remedy: On the U series machines ( actually the Duos as well ) the coolant water flow is as follows:
    Upper flush pump --> 2 way air-operated solenoid --> 1/2" or larger tubing or rigid piping (to the upper head assy) --> round SST manifold --> .8 mm orefice (inside manifold) --> spring loaded check valve -->
    --> 3mm plastic push-on tube to upper power contact face.
    The problem was that there was insanely low amounts of water getting to the contact, because there was a small piece of solid debris that got caught in the .8mm orefice.
    I've had an immature filter blowout ( more on that perhaps another time ) a while ago that introduced some solid particles into my clean tank.
    Obviously there are no additional filters after the jet pumps, so anything that gets sucked up must go though some of the outlets in the upper head.
    So, in my case the pump took in a small piece of junk and pushed it into the .8mm orefice, where it properly wedged itself.

    Procedure to the fix - while it may seem a bit daunting at first - is actually not that bad.
    You take out like 20 or so phillips screws to remove the upper-right cover (beige) from the head ( need power-on as you will need to move the Y axis to the extreme +Y and -Y position.
    Lower the Z axis to it's mininum, and take out 3 screw to remove the right side cover (black) from the head.
    Now you will see all the hoses - air and water - that is feeding the upper head.
    The large ( 2" dia ??? ) stainless thingy is the manifold, one large tube on top( inlet from pump ), elbow with large hose on the side ( outlet to flush ) and small hose on the bottom, which is the outlet
    port to a spring loaded check valve, and then further down to the power contact. That is the cooling path!
    So, by removing 4 hoses you can get the whole shebang in your hands.
    Disassembled the manifold, removed the orefice ( SST setscrew with a .8mm hole) reamed the hole to get rid of debris and sharp edge, cleaned the check valve and re-assembled the whole thing.

    Result: With the 3mm hose removed from the head, at Fluid Pressure setting @ 2, Override Upper @ 100, the water flow is a solid horizontal stream.
    Not a dribble, not a faint spray, but a solid stream that is strong enough to be horizontal for 6-8 inches.

    That's it!

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