Announcement

Collapse
No announcement yet.

How should I go about loosening knurled knob on centrifuge that's been overtightened?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • A.K. Boomer
    replied
    This is exactly why I stated the "obvious" back in post 6

    even if there's no protruding threads you can still for the most part figure out what direction thread it is - even if all you have is the end of the nut to look at - take your time, get a magnifying glass if you have too, whatever it takes because nothing is really more critical than knowing what direction to turn when going to "loosen",

    also - as I stated - any time something itself is rotational (centrifuge) there should be a big red flag going off about it possibly being a specific direction thread... many a apparatus is broken due to someone not wanting to take a quick few minutes to analyze the specifics...

    Leave a comment:


  • BCRider
    replied
    Another idea for things like this would be directional knurling or fluting that tends to let the hands slip more easily while tightening but obtain a harder grip for loosening.

    A bit of lettering tape on the lid might aid in this not occurring in the future.... well, perhaps not as often at least.

    It would not be that hard to make up a simple small strap wrench for something like this which uses a short length of 1/2 or 3/4" nylon webbing and a saw cut in the end of a bit of steel rod with a hole on the other end for a cross handle.

    Leave a comment:


  • EddyCurr
    replied
    Good practice on the part of the designer/manufacturer calls for markings to designate left hand threads. Big fail in this instance.

    The circumferential slots in the faces of wrench flats for hex fasteners is one method of marking (hose-to-gauge fittings on welding gas bottles is a familiar example.) Crescent shaped marks on the tops of fasteners is another and would have possibly prevented the situation in this case.

    Of course, awareness that fasteners are not always 'lefty, loosey' and that marks may or may not be present is essential.

    .

    Leave a comment:


  • Mike Amick
    replied
    Originally posted by winchman View Post
    I have no idea how anyone could have gotten it so tight. The threads are clean and undamaged.
    Probably trying reaalllllly hard to loosen it in the wrong direction.

    Leave a comment:


  • EddyCurr
    replied
    Well done. Imagine that produced a feeling of satisfaction.

    .

    Leave a comment:


  • winchman
    replied
    I was able to remove the entire rotor assembly from the centrifuge by removing the left-handed nut on the end of the shaft, but I still couldn't get the knob off with soft jaw pliers. So I chucked the knob in the 13" Tray-Top lathe, stabilized the rotor with the tailstock ram, and used a strap wrench to turn the rotor. There are no markings to indicate that the knob or shaft nut have left-handed threads, but both do.

    Fortunately the knob didn't slip in the chuck, so you can hardly tell it was gripped that way. I have no idea how anyone could have gotten it so tight. The threads are clean and undamaged.
    Last edited by winchman; 10-19-2016, 01:42 AM.

    Leave a comment:


  • macona
    replied
    Order another nut and once it gets there do whatever you need to get the old one off.

    Leave a comment:


  • enl
    replied
    Depending on the details of the machine, my answer could go several places.

    I like drilling holes for a face (pin) spanner, if it can be done without making a mess inside the unit, if there isn't a concern about the holes holding contaminants, and it can be done such that the balance won't be negatively affected. Might need to rebalance the nut or replace it with this option.

    If the knurling is straight, and time permit, I would probably make an internally splined driver to grab the knurl. Mount it to a ratchet so it can only be used in the loosening direction and make it part of the machines kit. Could maybe form one faster using epoxy, instead of machining one, at the risk of getting epoxy into the machine.

    If the knurling is straight and large enough pitch, an external driver could be made with three or more pins through a plate to grab the knurls. They would need to be on an appropriate circle and spaced to grab the ridges. Not a top precision job, as they can be tapered and slightly inset so they grip as the tool is pushed down over the nut. If needed, a ring around the pins will limit spread and maintain grip.

    Last option would be split it (if external) or core it (if internal) and get a replacement.

    Leave a comment:


  • KMoffett
    replied
    Does the red arrow indicate the direction of the trunnion's rotation? If it does, then a left hand thread would work. Most lab equipment manufactures have 24/7 tech support. Give them a call.

    What make/model?

    Ken

    Leave a comment:


  • EddyCurr
    replied
    Originally posted by A.K. Boomer View Post
    I know im stating the obvious here but it's a centrifuge so verify if the threads are left or right hand - hopefully they have enough hanging out to see or have a mark or warning label.
    Well noted. Cannot say I would have had that thought first thing at this time of the morning.

    Where there is one centrifuge, it seems that often another one is not too far away. If so, checking a similar unit would provide the definitive answer about thread direction.

    .

    Leave a comment:


  • EddyCurr
    replied
    Is the threaded portion of the knob internal (a nut) or external.

    If it is a nut, what about adding heat to increase the thread ID - or would the longitudinal expansion increase fastener stretch/retension, becoming counter-productive? If heat could be beneficial, a non-marring application method is by conduction - heat up a suitably sized chunk of somethinium and place on top of the knob, repeat as necessary until the knob is WARM with due thought to not getting the somethinium SO hot as to mar any finish on the knob.

    Alternatively, perhaps dry ice from your friendly welding gas distributer might work in the opposite manner?

    .

    Leave a comment:


  • Willy
    replied
    I'd say something along the lines of what Paul posted in post #3.
    Perhaps a thick piece of leather on the knurls and a chain grip wrench, or the leather in conjunction with a strap wrench.
    Leather the thickness of a good belt should suffice. As Lynnl mentioned being knurled it shouldn't take much to loosen it as it's only been tightened using the knurls and a good grip.
    Kind of like a screw on lens filter, seems almost impossibly tight until you use the right tool to unscrew it and then it almost falls off by itself.

    Leave a comment:


  • A.K. Boomer
    replied
    I know im stating the obvious here but it's a centrifuge so verify if the threads are left or right hand - hopefully they have enough hanging out to see or have a mark or warning label.

    then question if the machine can handle the static torque your about to apply without damaging it, or if there's a way of countering said torque by holding something lower than the knob,

    Paul's got a pretty good suggestion there with the strap wrench and keep in mind when using them to favor the ratchet handle to the outside of the drive shank as this will keep your torque ratio up instead of having some of it go to waste and be counterproductive...

    Leave a comment:


  • Noitoen
    replied
    Drill 2 little holes and use a pin spanner.

    Leave a comment:


  • kitno455
    replied
    Drive thin walled brass tube down onto it?

    allan

    Leave a comment:

Working...
X