LNC8 (94) control shutting off mid program


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Thread: LNC8 (94) control shutting off mid program

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    Default LNC8 (94) control shutting off mid program

    So, this has been a project for me in that I purchased this lathe not functioning and am getting it back up and running. I would consider myself a "mill" guy and am only a few years into machining. So fixing a machine, learning cnc lathe, learning a new control all at the same time. I know I am crazy. Short backstory on the machine. Its a 94 Okuma Cadet LNC8 with a 5020L control. Was working in a shop I worked in and the building was frequently exposed to power surges. One day this thing powered up after a storm the night before and had SVP start error. After a lot of research and trying a few suspect boards found the servo drive was smoked. I just purchased a reman unit and installed and bam, machine back up. Now after learning the control a bit and figuring out how to load posts, I created a simple test program, set my work offset, and launched it. Everything started fine, rapid over to the work piece and faced the part. As soon as it rapid in X+, I heard a breaker type click and the control shut off. It didn't trip the breaker on the shops control panel and I Still have power at the machine. I have to cycle the power on the side of the machine before the control will turn back on and reboot. Tried this a few more times and in the same section of the program it does the same thing. I am sure its an overcurrent issue caused by binding of the X axis or a damaged X servo. I know it could be a bunch of different things. This forum never ceases to amaze me in the amount of experience and knowledge that you guys have and are willing to share. I can pretty much handle anything that needs to be done once I know what needs to be done. So having said all of that, Has anyone run into this before and have any insight on what I should check next before I give a big pound of flesh to Gosiger to come look at this thing? Thank you very much in advance for all the help.

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    Last edited by ArtJ; 01-10-2021 at 11:44 AM.


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    Default Re: LNC8 (94) control shutting off mid program

    Congratulations. Make a list of possible causes and check all of them one-by-one.
    1. Could be because of overcurrent as you say. Try:
    - to create overcurrent situation in different ways. For instance, starting the spindle with maximum rpm and moving Z and X axis (rapid) positioning at the same time
    - the best is to make peak current measurements.
    - to make situation of overcurrent a bit easier - reduce feed rate, reduce spindle rpm.
    2. What I would start from. Did you moved the machine to another workshop?
    If yes, then:
    - check the level. double check. Triple check. I had in practice even saddle broken apart because of ( X ) guideways were twisted.
    - check the load percentage of each axis in full stroke length. The load shouldn't exceed 11% without load in any conditions and should be continuous.
    - wiring number one. If the mains cable cross-section is enough for your machine?
    - wiring number two. If there is main transformer ( very big one ) ? Check and double check wiring of the transformer. I have seen in my practice reverse connected. It gives desired voltage and some people think it is correct. No. Input does not serve as output.
    3. Check wiring of Controls power supply. Locate the exact place where the power is disconnected - this helps to understand the root cause.

    If you suspect that X drive causes the current surge, do the experiment: move Z, run spindle, don't touch X. And opposite: Leave spindle and Z in peace, move X only.



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    Default Re: LNC8 (94) control shutting off mid program

    So after working on the lathe for the last week I have come to realize the control shutting off mid program happens when the spindle decelerates or shuts off. I have heard that these machines are very picky about power input. Like, the voltage has to be an exact number or when the spindle motor decelerates will cause a raise that can do crazy things. It is currently hooked up to 3 phase directly from a panel in a shop. No conditioner or transformer is currently part of my setup. Anyone seen this before? Should I be running this on a transformer? I am about to go looking for exact power input requirement numbers now.



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    Default Re: LNC8 (94) control shutting off mid program

    Your idea is right - decelerating spindle can cause a voltage spike. You can check it quite easy to be sure about root of the problem: try to stop the spindle slower - set several steps lower speeds in the part program before M02 ( M30 ).
    If machine is without transformer, you don't need it. There are other measures to take, transformer is very expensive.
    Pay attention to cross sections of power supply wires. Double check the voltage range.
    And, of course, very valuable information would be if you find out the control device which is responsible for power off in case.
    Check if the spindle drive ( inverter ) is equipped with braking resistor. Should be. If the resistor is cold - means not working. The problem root can be exactly there.



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    Default Re: LNC8 (94) control shutting off mid program

    Thats great info. I am looking in to whats needed for input power and also researching the braking resistor. Not sure if thats an integral part of the VAC III or not. It sure seems like if there was something to stop the backfeed upon decel it would be fixed.



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    Default Re: LNC8 (94) control shutting off mid program

    braking resistor should be quite big and easy visible with separate cooler or radiator at least



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    Default Re: LNC8 (94) control shutting off mid program

    I found out the braking resistor is part of the vac III drive. My problem could be high impedance on the buildings electrical. Also the spindle is not running at the requested speed. If I ask for 1000 rpm it runs 836 with the override set on 100%. And the spindle speed does not obey the override switch either. Takes 3 clicks in either direction to change spindle speed at all. Seems like the more I look, the more gremlins I am finding.



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    Default Re: LNC8 (94) control shutting off mid program

    Indicates power supply weakness. You can see the voltage drop at the spindle drive terminals when commanding the spindle run. If it is the case, you just need to check and arrange proper power lines connection - copper wires, big cross sections. For Okuma you don't need any calculation though. Simple rule - take the copper wire with biggest cross section which fits into the connection terminals.



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    Default Re: LNC8 (94) control shutting off mid program

    So it turns out the machine was in low gear. I am used to haas mills where they switch automatically. I gave it an M42 in mdi and all my spindle speed problems are gone. I also see that max rpm in low gear is 850. So now I am only left with the power issue where it shuts off every time the spindle decelerates. I see the wiring from the panel to the machine is 8 AWG and is around 400 feet from the power panel to the lathe. I am considering getting a Maddox transformer and putting it lose to the machine. I am still wondering if I should shorten up the wiring from the panel to the transformer. Or if I shorten the wiring do I even need a transformer. Anyone know the exact power recommendations for this machine? I mean, I see the badge on the side that says 220V 3ph 60hz 13.4KVA 35.2A Full load current 36.6A largest motor current rating 25KA interrupt capacity. Incoming voltage is 208V. Just wondering what I should do from here.



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    Default Re: LNC8 (94) control shutting off mid program

    4 AWG ( about 10mm²) for sure is not enough for 35A.



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    Default

    Quote Originally Posted by Algirdas View Post
    4 AWG ( about 10mm²) for sure is not enough for 35A.

    Well, it turns out what was wrong with the powering down during decelerating spindle was a damaged 124V power supply. Replaced that and now the machine is still 100%. I have made some parts on this thing and now am working on getting a Fusion Post Processor tweaked to work with the old girl.



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