Wohlenberg Type 115 blade not stopping at top dead center

Discussion in 'Cutters and Trimmers' started by Graytell, Sep 1, 2017.

  1. Graytell

    Graytell Member

    Joined:
    Mar 2008
    Messages:
    7
    Location:
    Queensland Australia
    Wohlenberg Type 115 Programmatic.
    On this machine the blade sometimes stops in the right place but most times will move past the top and begin moving down after the cut and then stop. Being dangerous because the blade protrudes below the clamp. When it does this the back guage can not be moved forward only backward.
    The stopping position is variable( ie is does not stop in the same place all the time).
    I have swaped relays on the relay boards to see if I could get it to act differently but found no change.
    I have checked the limit switches on the cams and they seem OK but could be still malfunctionig in some way.
    The switch on the short cam lobe does pass over the cam and stop on the other side when the blade goes furtherest past top dead centre. When this happens the backguage can not be moved forward
    If I force the limit switch on that lobe to switch early the blade will stop earlier but when I do this I can not determine if the stopping point is still variable or not
    Does anyone have an idea what could be causing this?
    Regards
    Graytell
     
  2. CHOCK

    CHOCK Senior Member

    Joined:
    Dec 2016
    Messages:
    2,852
    Location:
    Managua,Nicaragua
    Hi sir
    Good day
    Let me know, what is his problem in Wohlenberg
    Maybe I can help you.
    However this is a matter of Time Cam vs Limit Switch.
    Try to tigh the bolt for Cam, and see his marks are correct. Tight the wires for limits switchs
    open the L.Ss and see carefully it is necessary with Zoom Magnifier, and see if there are Broken, dirty
    or contacts wears. Try to clean very well with solvent for contacts, repair or Replace, and tight very well
    his connection. See if the connector for L.Ss are o.k or broken, or dirty, or with oil, clean it, and tigh very well
    see carefully if the PINS are NOT broker, or bend.
     
  3. Graytell

    Graytell Member

    Joined:
    Mar 2008
    Messages:
    7
    Location:
    Queensland Australia
    Hi Super Chock,
    Thank you for your effort to help with this.
    We have done as you suggested and at this time have not found the problem.
    There is something that does not add up for me. The fact that the stopping point is variable leads me to think that there is some other control that stops the blade at the top, the variation could be as much as an inch or 25mm in blade height. Non of the cam limit switches are snap action as could be expected if they were to time the stopping point. Also there does not seem to be timing marks on or near the cams as you suggest to check. The only marks are two arrows on the gearbox and the gear crank which should be adjacent to one another when the blade is at rest.
    Your thought may have been loose wires or broken limit switch springs. The switches have clear plastic sealed covers on them so it is difficult to gain access to the contacts except to view them through the plastic We have checked and there seems no variability in how they operate.
    If we move the short lobe cam a small amount we can not tell if the blade stopping position is effected due to the variability of the stopping point.
    The blade will stop its downward travel when the limit switch on the small cam lobe drops off the far side of the lobe (This switch must act as a safety override when this happens) but sometimes that limit switch will stop on the top of the lobe when the blade stops closer to the top just as it should, but it never seems to stop in the same position twice.
    Do you know if there is something in the control box that may remove the variability encountered.

    Regards
    Graytell
     
  4. CHOCK

    CHOCK Senior Member

    Joined:
    Dec 2016
    Messages:
    2,852
    Location:
    Managua,Nicaragua
    Hi sir.
    Hope you are well.
    Well i can understand this situation. However
    1) I am supposing the machine is Older. and the system too.
    2)Sometimes you must use the technic proof and error.Some person
    in front pushing cut-button and other person in Gear box -Level Cam, and Moving the Cam until the knife is Stop in the Upper most possition.This is very Important point.
    See if the machine has Safety Bolt, if have this must take out, in order to avoid some Rupture
    of the machine, and test the Safety Bolt rear of the machine(Lube and test the Sensor or l.switch),test it for lack of voltage, or loose wire, or defective winding(reheating)/
    3) With the DMM (machine OFF very important) or tester you must measure the Continuity contact of Limit Switch, N.O and N.C, since if some of them they are broken or wear or dirty, the adjustment Timing Cam, will be NOT possible. Use the Schematic Diagram for to see what contacts are N.O and N.C.
    4)The schematic diag will be reveal that section for this L. Switch and show what contact is N.O and N.C for most easy time adjustment Cams-level , in order to close Relais,etc.
    If you have schematic diagrams in PDF , please send me to my email, in order to guide you most deeply.
    or if you do not have send me Pics of the machine front and back , for to see what model is, and can search for some schematic and help most effective.
    Let me know any question or doubt ASAP.
     
  5. Scopesys

    Scopesys Member

    Joined:
    Dec 2014
    Messages:
    36
    Location:
    East Coast USA
    The mechanical CAM Switches on all Wohlenberg Cutters, eventually give operational issue, because they basically "wear out",
    As Chock advises, the 1st thing to do is to measure their Closed contacts with a multi-meter (WITH THE POWER OFF).
    Typically, if their resistance are much over 1 ohm, they are failing, and need to be replaced, to re-achieve reliable operation.
    Sometimes you just have bite the Bullet and replace old worn out parts .. Electro-Mechanical parts do not last for ever.

    With unreliable . intermittent, high resistance Cam Switches, you will spend far more time (=Money), messing with them, trying to get the system to work reliably (and you never will), until you replace them, so it's far less costly to do that first !!!

    WARNING: The original Cam Switches that Wohlenberg fitted to their Cutters, worked well during their lifetime, but have for some time, been discontinued by their manufacturer.
    Be careful in selecting a replacement .. Not all similar looking can switches work equally well on the Wohlenberg.
     
  6. Pixelated

    Pixelated New Member

    Joined:
    Sep 2018
    Messages:
    3
    Location:
    Australia
    Hi Graytell. one other thing that can cause this issue, is wear on the clutch disc linings which drives the knife.
    The clutch is spring loaded onto the braking ring, then when you press the cut buttons, power is applied via the slip rings to the clutch which magnetically attracts the clutch onto the driving ring. If the lining on the drive side becomes too worn, the magnetic air gap becomes too small, then when the knife returns to TDC, it takes too long for the magnetic field to drop sufficiently too allow the clutch to snap back to the braking ring which can cause the knife overrun.
    The drive and brake rings are fairly easy to adjust, but one must be careful with the 3 allen screws in each ring that lock the ring in position and make sure that they tighten onto the cutouts in the threads
    Also, with regard the cam switches, I have been able to source more of these from RS components here in AU
    This link is to what they have https://au.rs-online.com/web/p/safety-limit-switches/4107408/?sra=pstk
    Cheers,
    Rob
     

  7. Scopesys

    Scopesys Member

    Joined:
    Dec 2014
    Messages:
    36
    Location:
    East Coast USA
    Also, check the Clutch Suppressor ( The device wired across the clutch coil)
    A defective or intermittent suppressor will alter the time it takes the clutch to turn off, and the brake to turn back on .. thus altering the TDC stop position.
     
Loading...