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Unseating a Jammed Gib

When a Lucas boring mill 'Jams' or 'Sucks' a tapered gib, it is not obvious how to free the gib and the slide so that repairs can proceed.

Do NOT attempt to hammer the gib free and do NOT attempt to use a jack or a press. The gib is too soft a material for that to work. You will either break off the gib or 'mushroom' the end and make it even harder to remove. If you have already 'mushroomed' the small end of the gib it will be necessary to carefully cut off the swelled end before proceeding. Be careful; the slightest touch of a tool while cutting off the end of the gib will damage the ways!

 

 

The reason for the described process is as follows:

  1. The gib has been 'seated' like a giant tapered pin by the drive system of the machine.
     
  2. The side of the gib against the way likely has a 'rolled up' burr of metal partially embedded into the gib and partially embedded into the way.
     
  3. To remove the gib by hammering or jacking would require you to simultaneously 'un-seat' the taper and shear the 'rolled up' burr.
     
  4. The correct process is to lock the gib against motion and move the slide off the non-moving gib. This avoids the need to shear the burr. It is only necessary to 'un-seat' the 'jammed' taper.

 

 

Removal Process:

  1. Cut a piece of piece of flat stock to brace the small end of the gib. The stock should be 1/8 inch smaller than the small end of the gib (in cross-section) and long enough to reach to the solid structure at the end of the machine ways. 'Barber' the length of the piece to fit as close to exactly as possible (within a few thousands of tight).
     
  2. Clamp the flat stock to the ways so that it cannot bow. Pad the clamps.
     
  3. Remove all tubing, fittings, hose, electrical switches, etc from the area around the large end of the gib.
     
  4. Remove all gib mounting hardware.
     
  5. Pad the area around the large end of the gib with hardwood planks. Oak is preferred. You must not have a wood that will absorb the force of the blows and you must not have a wood that will bend when it is struck.
     
  6. Position a 'helper' at the machine hand crank to hold firm, steady pressure on the leadscrew in the same direction that you will be moving the slide away from the gib. He should not apply so much pressure to the hand crank that he might damage something. His purpose is to constantly maintain the nut to leadscrew backlash in such direction that the screw and nuts do not absorb the blows to the slide, which will damage them and make it more difficult to 'un-seat' the gib.
     
  7. Apply repetitive blows to the face of the wood planking. You will need a weight of several hundred pounds. There is no 'standard' for how much is enough and how much is too much. There is no standard for how hard to swing the weight. You need to recall that if you hit it too hard - it may crack the main castings and scrap the entire machine. There is no standard for how long you will need to apply the blows. Sometimes only a few blows are needed. Sometimes it may require several thousand blows over several shifts.
     
  8. This job CANNOT be 'hurried'. Hurrying will cause you to strike too hard and destroy the machine.
     
  9. You will probably NOT SEE any visible or even measurable slide movement until you are within the last few blows before it releases. The gib is tapered 1/8 Inch per foot which is approximately 0.010 inches per inch of length. A 0.002 interference (like a press fit) between the gib and the ways will only require moving the slide approximately 0.200 to relieve the 'jam up'.