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Frozen knee...need help!!!

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  • Frozen knee...need help!!!

    I need to ask you guys a couple questions before I go any further.
    The knee is rusted solid...I think.
    I've been carefully jacking on it enough to put a little pressure on it then release it then jack it up again etc. Sort of trying to rock it loose. Done this about 100 times or so.
    Now I'm not sure. It could be that the jackscrew is siezed...I don't know.
    Here,s a pic of it....

    I have both setscrews out of it and the 1/2" bolt is only in by a thread.
    This thing was outside for a couple years.
    If the knee wasn't rusted...would the jackscrew just pull out if the top collar was loose and had the setscrews out of it?
    If not...do you think the bottom of the screw could be siezed in some sort of collar that is part of the base?
    I've never worked on a knee before and have no idea what is under the base.
    I just want to rule out the screw.
    I turned the handwheel back and forth from underneath. It moves, the bevel gear moves back and forth a bit but the screw doesn't seem to want to move.
    Possibly or more likely it;s because of the frozen knee but I'm not sure.
    Thanks!
    Russ
    I have tools I don't even know I own...

  • #2
    Have you tried applying Kroil to break the rust bond?


    HTRN
    EGO partum , proinde EGO sum

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    • #3
      Yes! I've been pumping it in all afternoon. Was hoping the rocking motion would speed it up.
      Russ
      I have tools I don't even know I own...

      Comment


      • #4
        You gotta give it time to work - try letting it sit overnight. If that doesn't work, mebbe some light heat will break the bond. You might even wanna try giving it a couple good hard wacks on the side with soft faced hammer, just to upset the bond.


        HTRN
        EGO partum , proinde EGO sum

        Comment


        • #5
          Hehehehe...I know...I'm being impatient.
          I figured it'd be a huge job to get this going but I've got so much done today I'm getting anxious. I just need to see if a few more things work before I decide to tear it down.
          If there is something major hooped on it it'll have to wait. Still hoping for the best.
          I have tools I don't even know I own...

          Comment


          • #6
            Rust? You call that rust?

            Russ,I am assuming you released the knee lock right? If you did,you may have to loosen off the gibs on the dovetails to get it moving.

            So far as what's in the knee,the bevel gear usually sits on the top of the elevation screw keyed to it of course,above that is a ball or roller thrust bearing and a stub end on the shaft that slips into a bore in the knee casting,the whole mess depends on gravity to hold it down so jacking on the table shouldn't hurt so long as you don't use all of that 20 ton jack
            I just need one more tool,just one!

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            • #7
              Speaking of gibs, if you want to pull teh knee, have you removed or at least loosened the gib? With the gib holding it closely, not only would it be locked if there is any rust in there, but you might score the ways getting it off of there if you CAN move it.

              And then, you don't know but that it is cracked and digging in somewhere......
              1601

              Keep eye on ball.
              Hashim Khan

              Comment


              • #8
                Darin, the only lock for the knee that I can see is a 1/2" setscrew with a folding kinda handle on it. I took it right out and soaked the hole with Kroil.
                Both of you...What was I thinking? I never even thought of loosening the gib.
                There seems to only be one lock screw at the bottom of the gib. The screw faces up. Must have to release that I guess.
                Never made any headway the whole night but that's ok...I never broke anything either.
                Sat there for hours lifting and lowering the knee....a whole .001.
                I put a DI on the column and indicated off the swivel base.
                Lift and lower, squirt more Kroil....repeat, repeat, repeat.
                I did get the jack screw loose though. Once the Kroil soaked in I spun the collar right out. So it isn't the jack screw for sure.
                Tomorrow I'm going to remove the gib...put a little preasure on the knee and run an air chisel with a pad on it up and down the dovetails.
                Russ
                I have tools I don't even know I own...

                Comment


                • #9
                  I can recall a couple of instances where I have seen the knee of a Bridgeport siezed on the column. In those cases, it seemed the gib had somehow managed to wedge the whole works tight. Needless to say, the gib had to be loosened to facilitate movement of the knee, and that had to be done by actually driving the gib loose with a hammer and drift.

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                  • #10
                    Originally posted by torker
                    I

                    I just want to rule out the screw.
                    I turned the handwheel back and forth from underneath. It moves, the bevel gear moves back and forth a bit but the screw doesn't seem to want to move.
                    Possibly or more likely it;s because of the frozen knee but I'm not sure.
                    Thanks!
                    Russ
                    Ok lets look at this logically one step at a time.
                    The hand wheel moves as does the bevel gear but the screw doesn't.
                    So why not? Two reasons, one is it's rusted into the nut and secondly it's rusted at the top bearing housing.
                    Forget the knee for now because if the knee is / was rusted firm you would still have movement in this screw, no screw is that backlash free.

                    Getting to the top bearing isn't easy as it's inside the knee but you have to strip this to clean it anyway.

                    Personally I'd start by removing the bed. Free off the gib strip, remove the end brackets holding the screw and unwind the screw from the nut and the table will be able to be lifted off by two people.

                    Then do the same for the cross axis or Y axis and get this clear.

                    At this stage you should now be able to look down into the knee and see the bevels.

                    The bevels are usually held on by taper pins to act as shear pins. Look carefully when trying the handle to see if there is any movement at the top, if you can see the bevel move but not the shaft then the top bearing is siezed.
                    If they move together then the problem is the nut.

                    Address this problem first and forget the actual knee at this point, work logically.

                    .
                    .

                    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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                    • #11
                      x39, Thanks, that is todays project. Have to figure out how they have the gib anchored.
                      John, Thanks also!
                      I took the table off before I brought this home (ouch...by myself....table is very heavy)
                      I found last night that the screw was indeed rusted into the nut at the bottom. I've got that freed up now.
                      Now it's getting the knee loose.
                      I am no longer in a hurry....this'll take awhile.
                      Russ
                      I have tools I don't even know I own...

                      Comment


                      • #12
                        Originally posted by John Stevenson
                        if the knee is / was rusted firm you would still have movement in this screw, no screw is that backlash free..
                        Not to put too fine a point on things, but theoretically and for the sake of interesting discussion, if the last person to move the knee cranked it down, any backlash would already be taken up. This is because when cranking the knee down, the weight of the knee actually "rides" the screw downward. Should the knee sieze under this condition, it would be very difficult indeed to get any movement out of the screw.

                        Comment


                        • #13
                          Russ-- you want to not only remove the "lock screw" you referred to for the gib, but there should be an adjusting screw. Often these would be accessible from the top of the knee which may be a negative in your case as it could easily be rusted and you have to be able to back it out to back the gib out. In short, you should be able to *remove* the gib. Be careful as the knee could tip at that point. Once there is no gib, nothing short of a weld would keep the knee from being popped loose....except the screw. By getting to this point, you can alleviate the question of whether it is column to knee way corrosion or problems with the screw itself.

                          Kroil is the oil that creeps....but you have to let it creep and creeping through iron oxide can take a while. I would think in terms of days or a week and not hours. Patience may save you broken parts which may not be available for that mill.

                          Still, it would pay to get the gib out of the way, because for all you know, it could have been bound up independent of any oxidation on the way surfaces because as John pointed out, you need to isolate where things are binding. If you can get everything that constrains the gib (locks, adjustments etc) out of the way, I would then consider using a drift (gently) on the end of the gib to pop it loose. Be sure you are going the right direction with it. All that assumes that you can see both ends of the gib and that is it a standard tapered gib.
                          Paul Carpenter
                          Mapleton, IL

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                          • #14
                            Johns advice is superior to anything I can offer but if you decide to apply heat try a hot air gun {paint stripper type) as you dont want naked flame heat like a blowtorch as it will do more harm than good good luck take your time dont force anything too hard you don't want to break anything irreplacable regards and good luck Alistair ps this is exciting
                            Please excuse my typing as I have a form of parkinsons disease

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                            • #15
                              I played with the gib a bit before work this morning.
                              The lock screw is out.
                              There is a 12 point bolt in the bottom. It loosened easily but only backed out a couple of turns and is solid. I'm guessing there is a pocket in the gib or something that captivates it.
                              The gib is also rusted so it won't move either.
                              I'm going to make a punch to fit it and tap it a bit to see if it'll loosen.
                              I agree, the gib is the key to this. If I can budge it the knee would almost fall off...lol!
                              Russ(covered in Kroil)
                              I have tools I don't even know I own...

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