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knee stuck - gib is jammed

jkeyser14

Cast Iron
Joined
Oct 18, 2005
Location
MD
I was using a bridgeport style mill today, and when going to raise the z-axis, there was a loud pop. I looked, and the z-axis gib had popped past the adjustment screw meant to tighten it in place. As a result, the gib is wedged extremely tightly in between the column and the knee.

I took the gib adjustment screws completely out, tried to lube everything as best as I could, and used a long lever arm to try to push the gib back up into place. It didn't budge (I bent a piece of 1.5" box tubing w/ .125" walls). I also tried hammering on a short lever arm w/ a dead blow hammer just to dent up the base of the mill.

Then I decided to try to wiggle the knee back and forth a few times to see if that would loosen the gib - big mistake. The gib is now wedged in even further and the z-axis handle is now toothless (it was cast and already missing some teeth).

Tomorrow I am going to try to find a small jack to put under the gib, but I'm not sure if it will be easy to position due to the shape of the base.

Does anyone have any suggestions? I was told that someone had previously done the same thing to this mill and it took a jack along w/ a lot of hammering to fix the problem.
 
I was using a bridgeport style mill today, and when going to raise the z-axis, there was a loud pop. I looked, and the z-axis gib had popped past the adjustment screw meant to tighten it in place. As a result, the gib is wedged extremely tightly in between the column and the knee.

I took the gib adjustment screws completely out, tried to lube everything as best as I could, and used a long lever arm to try to push the gib back up into place. It didn't budge (I bent a piece of 1.5" box tubing w/ .125" walls). I also tried hammering on a short lever arm w/ a dead blow hammer just to dent up the base of the mill.

Then I decided to try to wiggle the knee back and forth a few times to see if that would loosen the gib - big mistake. The gib is now wedged in even further and the z-axis handle is now toothless (it was cast and already missing some teeth).

Tomorrow I am going to try to find a small jack to put under the gib, but I'm not sure if it will be easy to position due to the shape of the base.

Does anyone have any suggestions? I was told that someone had previously done the same thing to this mill and it took a jack along w/ a lot of hammering to fix the problem.
 
I was using a bridgeport style mill today, and when going to raise the z-axis, there was a loud pop. I looked, and the z-axis gib had popped past the adjustment screw meant to tighten it in place. As a result, the gib is wedged extremely tightly in between the column and the knee.

I took the gib adjustment screws completely out, tried to lube everything as best as I could, and used a long lever arm to try to push the gib back up into place. It didn't budge (I bent a piece of 1.5" box tubing w/ .125" walls). I also tried hammering on a short lever arm w/ a dead blow hammer just to dent up the base of the mill.

Then I decided to try to wiggle the knee back and forth a few times to see if that would loosen the gib - big mistake. The gib is now wedged in even further and the z-axis handle is now toothless (it was cast and already missing some teeth).

Tomorrow I am going to try to find a small jack to put under the gib, but I'm not sure if it will be easy to position due to the shape of the base.

Does anyone have any suggestions? I was told that someone had previously done the same thing to this mill and it took a jack along w/ a lot of hammering to fix the problem.
 
YES!! I've successfully salvaged seven machines in this situation and seen maybe a dozen that were botched resulting in cracked knee or column casting.

Stop. Ignore all conflicting advice especially if it seems easier. The only safe solution for a stuck knee gib is a heroic remedy.

You've described a classic stuck knee gib. You are very close to permanently damaging the machine's knee or the column. By permanently damaging I mean cracking the column or knee at the interior angle of the dovetail. Further movement of the knee or the gib in the wrong direction has to be avoided at all cost.

Tear down the machine removing the table, saddle and turret (leaving the ram and head in place if you can handle them safely assembled). Remove the elevating screw, gears, elevating shaft and gears, and internal lube fittings from the knee. The knee gib adjustors have laready been removed you say. Obtain a piece of plate about 10" wide x 3/4 or more thick by long enough to bridge the turret diameter plus 5". Use thin cardboard to protect the scraped surface from the rough plate. Drill four 9/16 holes on 2" centers along a radius to pass the turret clamping bolts through about 6" back from the front edge. Make a piece of 1/2 thick x 10" wide steel plate long enough to span from the turret to the knee. Position it to clear the gib. Fit this plate carefully so it gets good bearing between its ends and the knee and the turret plate. Do not use wood.

Assemble the plate over the turret opening and attach with the turret clamping bolts using lengths of pipe to make up the difference in bolt grip. Install the other plate between the turret face and the top of the knee where the felt wiper would go. Apply some downward force but do not try too shift the knee at this time. Merely snug up the nuts. The object of the turret face plate and the peice down the from its to keep the knee from rising with the gib as it's tested.

Lay the column on its back, blocking it with timber so it does not roll. Drill a hole in the base casting in line with the knee gib and excavate with a die grinder to pass through a punch in line with the gib. Make a 1" dia steel punch about 2 ft long and make the end a parallelogram slightly smaller than the gib. Place it in the excavated hole and position it against the small end of the gib. Bump it firmly but not vigorously with the largest hammer available. If the gib does not move it's time for heat inside the knee.

Secure a large oxy-acetylene outfit with a rosebud tip. Heat inside the knee only the whole of the casting between the dovetails. Do not heat the column. I refer to the clearance metal of the knee between the docetails and not the masses that include the dovetails. Keep the torch moving and avoid localized heating. This will expand the knee casting without harm. The expansion will release the tension on the dovetail and relax the force on the gib. Have your helper test the gib by bumping with the hammer from time to time. As the knee warms and the metal expaands sooner or later the gib will become free.

This is a job that takes hours or days to set up but only minutes to execute. It has low surgcal risk when done correctly.

Work over all parts paying close attention to the knee and its gib. clean up and inspect the divertail interior angles for inspection under magnification. Dies check for cracks. If there are cracks present there is no permanent repair possible that does not involve replacemet or welding of a major casting. A repair of a sort may be made using IronTite repair technique perpendicular to the crack plane. This keeps the crack from spreading. Google "IronTite."

Remedy all defects particularly those having to do with the gib adjustors. If the gib will not adjust correctly use a brass shim behind it to compensate for wear. Clean and reassenble in the usual way noteing condition and wear as you go unless there is cause for immediate re-scraping and reconditioning.

Any solution that involves hydraulic jacks, heavy hammering, or avoids machine disassembly may damage or complicate the fix.

Beause of the gravity of the original poster's sutuation, I ask others to not contribute to this thread unless they have actual experience as a machine tool mechanic in a remedy of this particular problem. A single lucky break or "a guy told me" does not qualify as experience.

Please forgive my arrogance but this situation warrants careful procedure. Conflicting advise will jeapordize an expensive and hard to replace machine tool.

[ 05-20-2007, 08:17 AM: Message edited by: Forrest Addy ]
 
YES!! I've successfully salvaged seven machines in this situation and seen maybe a dozen that were botched resulting in cracked knee or column casting.

Stop. Ignore all conflicting advice especially if it seems easier. The only safe solution for a stuck knee gib is a heroic remedy.

You've described a classic stuck knee gib. You are very close to permanently damaging the machine's knee or the column. By permanently damaging I mean cracking the column or knee at the interior angle of the dovetail. Further movement of the knee or the gib in the wrong direction has to be avoided at all cost.

Tear down the machine removing the table, saddle and turret (leaving the ram and head in place if you can handle them safely assembled). Remove the elevating screw, gears, elevating shaft and gears, and internal lube fittings from the knee. The knee gib adjustors have laready been removed you say. Obtain a piece of plate about 10" wide x 3/4 or more thick by long enough to bridge the turret diameter plus 5". Use thin cardboard to protect the scraped surface from the rough plate. Drill four 9/16 holes on 2" centers along a radius to pass the turret clamping bolts through about 6" back from the front edge. Make a piece of 1/2 thick x 10" wide steel plate long enough to span from the turret to the knee. Position it to clear the gib. Fit this plate carefully so it gets good bearing between its ends and the knee and the turret plate. Do not use wood.

Assemble the plate over the turret opening and attach with the turret clamping bolts using lengths of pipe to make up the difference in bolt grip. Install the other plate between the turret face and the top of the knee where the felt wiper would go. Apply some downward force but do not try too shift the knee at this time. Merely snug up the nuts. The object of the turret face plate and the peice down the from its to keep the knee from rising with the gib as it's tested.

Lay the column on its back, blocking it with timber so it does not roll. Drill a hole in the base casting in line with the knee gib and excavate with a die grinder to pass through a punch in line with the gib. Make a 1" dia steel punch about 2 ft long and make the end a parallelogram slightly smaller than the gib. Place it in the excavated hole and position it against the small end of the gib. Bump it firmly but not vigorously with the largest hammer available. If the gib does not move it's time for heat inside the knee.

Secure a large oxy-acetylene outfit with a rosebud tip. Heat inside the knee only the whole of the casting between the dovetails. Do not heat the column. I refer to the clearance metal of the knee between the docetails and not the masses that include the dovetails. Keep the torch moving and avoid localized heating. This will expand the knee casting without harm. The expansion will release the tension on the dovetail and relax the force on the gib. Have your helper test the gib by bumping with the hammer from time to time. As the knee warms and the metal expaands sooner or later the gib will become free.

This is a job that takes hours or days to set up but only minutes to execute. It has low surgcal risk when done correctly.

Work over all parts paying close attention to the knee and its gib. clean up and inspect the divertail interior angles for inspection under magnification. Dies check for cracks. If there are cracks present there is no permanent repair possible that does not involve replacemet or welding of a major casting. A repair of a sort may be made using IronTite repair technique perpendicular to the crack plane. This keeps the crack from spreading. Google "IronTite."

Remedy all defects particularly those having to do with the gib adjustors. If the gib will not adjust correctly use a brass shim behind it to compensate for wear. Clean and reassenble in the usual way noteing condition and wear as you go unless there is cause for immediate re-scraping and reconditioning.

Any solution that involves hydraulic jacks, heavy hammering, or avoids machine disassembly may damage or complicate the fix.

Beause of the gravity of the original poster's sutuation, I ask others to not contribute to this thread unless they have actual experience as a machine tool mechanic in a remedy of this particular problem. A single lucky break or "a guy told me" does not qualify as experience.

Please forgive my arrogance but this situation warrants careful procedure. Conflicting advise will jeapordize an expensive and hard to replace machine tool.

[ 05-20-2007, 08:17 AM: Message edited by: Forrest Addy ]
 
YES!! I've successfully salvaged seven machines in this situation and seen maybe a dozen that were botched resulting in cracked knee or column casting.

Stop. Ignore all conflicting advice especially if it seems easier. The only safe solution for a stuck knee gib is a heroic remedy.

You've described a classic stuck knee gib. You are very close to permanently damaging the machine's knee or the column. By permanently damaging I mean cracking the column or knee at the interior angle of the dovetail. Further movement of the knee or the gib in the wrong direction has to be avoided at all cost.

Tear down the machine removing the table, saddle and turret (leaving the ram and head in place if you can handle them safely assembled). Remove the elevating screw, gears, elevating shaft and gears, and internal lube fittings from the knee. The knee gib adjustors have laready been removed you say. Obtain a piece of plate about 10" wide x 3/4 or more thick by long enough to bridge the turret diameter plus 5". Use thin cardboard to protect the scraped surface from the rough plate. Drill four 9/16 holes on 2" centers along a radius to pass the turret clamping bolts through about 6" back from the front edge. Make a piece of 1/2 thick x 10" wide steel plate long enough to span from the turret to the knee. Position it to clear the gib. Fit this plate carefully so it gets good bearing between its ends and the knee and the turret plate. Do not use wood.

Assemble the plate over the turret opening and attach with the turret clamping bolts using lengths of pipe to make up the difference in bolt grip. Install the other plate between the turret face and the top of the knee where the felt wiper would go. Apply some downward force but do not try too shift the knee at this time. Merely snug up the nuts. The object of the turret face plate and the peice down the from its to keep the knee from rising with the gib as it's tested.

Lay the column on its back, blocking it with timber so it does not roll. Drill a hole in the base casting in line with the knee gib and excavate with a die grinder to pass through a punch in line with the gib. Make a 1" dia steel punch about 2 ft long and make the end a parallelogram slightly smaller than the gib. Place it in the excavated hole and position it against the small end of the gib. Bump it firmly but not vigorously with the largest hammer available. If the gib does not move it's time for heat inside the knee.

Secure a large oxy-acetylene outfit with a rosebud tip. Heat inside the knee only the whole of the casting between the dovetails. Do not heat the column. I refer to the clearance metal of the knee between the docetails and not the masses that include the dovetails. Keep the torch moving and avoid localized heating. This will expand the knee casting without harm. The expansion will release the tension on the dovetail and relax the force on the gib. Have your helper test the gib by bumping with the hammer from time to time. As the knee warms and the metal expaands sooner or later the gib will become free.

This is a job that takes hours or days to set up but only minutes to execute. It has low surgcal risk when done correctly.

Work over all parts paying close attention to the knee and its gib. clean up and inspect the divertail interior angles for inspection under magnification. Dies check for cracks. If there are cracks present there is no permanent repair possible that does not involve replacemet or welding of a major casting. A repair of a sort may be made using IronTite repair technique perpendicular to the crack plane. This keeps the crack from spreading. Google "IronTite."

Remedy all defects particularly those having to do with the gib adjustors. If the gib will not adjust correctly use a brass shim behind it to compensate for wear. Clean and reassenble in the usual way noteing condition and wear as you go unless there is cause for immediate re-scraping and reconditioning.

Any solution that involves hydraulic jacks, heavy hammering, or avoids machine disassembly may damage or complicate the fix.

Beause of the gravity of the original poster's sutuation, I ask others to not contribute to this thread unless they have actual experience as a machine tool mechanic in a remedy of this particular problem. A single lucky break or "a guy told me" does not qualify as experience.

Please forgive my arrogance but this situation warrants careful procedure. Conflicting advise will jeapordize an expensive and hard to replace machine tool.

[ 05-20-2007, 08:17 AM: Message edited by: Forrest Addy ]
 
The first B/P I owned suffered from this same problem,and i suspect it had been caused by huge overload on the table.At any rate,the whole works must have wound up on the base,table and all!FORREST ADDY has described the probable only way to correct it,and i wont relate how the WOOD CHUCKS solved this one!Take the time,and do it right.
regards LEE RUSS
 
The first B/P I owned suffered from this same problem,and i suspect it had been caused by huge overload on the table.At any rate,the whole works must have wound up on the base,table and all!FORREST ADDY has described the probable only way to correct it,and i wont relate how the WOOD CHUCKS solved this one!Take the time,and do it right.
regards LEE RUSS
 
The first B/P I owned suffered from this same problem,and i suspect it had been caused by huge overload on the table.At any rate,the whole works must have wound up on the base,table and all!FORREST ADDY has described the probable only way to correct it,and i wont relate how the WOOD CHUCKS solved this one!Take the time,and do it right.
regards LEE RUSS
 
don't ever hammer on a gib
unless you can move it by hand
or adjust it normally by the screw
it cannot be moved

I solved a similar problem on my small
knee mill by moving the knee by hand, by
lifting on one side from underneath the table,
extending the table towards one side.

You cannot use a lever or mechanical force or you break the table. Just hand pressure.

For those with a less serious problem, easy to fix.

Easy does it. No force anywhere. Lots of feel.
If that doesn't work, forget the whole thing.

Or use the advise above.
 
don't ever hammer on a gib
unless you can move it by hand
or adjust it normally by the screw
it cannot be moved

I solved a similar problem on my small
knee mill by moving the knee by hand, by
lifting on one side from underneath the table,
extending the table towards one side.

You cannot use a lever or mechanical force or you break the table. Just hand pressure.

For those with a less serious problem, easy to fix.

Easy does it. No force anywhere. Lots of feel.
If that doesn't work, forget the whole thing.

Or use the advise above.
 
don't ever hammer on a gib
unless you can move it by hand
or adjust it normally by the screw
it cannot be moved

I solved a similar problem on my small
knee mill by moving the knee by hand, by
lifting on one side from underneath the table,
extending the table towards one side.

You cannot use a lever or mechanical force or you break the table. Just hand pressure.

For those with a less serious problem, easy to fix.

Easy does it. No force anywhere. Lots of feel.
If that doesn't work, forget the whole thing.

Or use the advise above.
 
I had a small screw get down into the gib space and lodge securely. I used my cherrypicker to unload the knee, removed the gib adjuster and and way wiper then with a combination of the machine's lifting handle and my hoist strapped around the table was able to hold the knee up and to the left enough that I could get in below the gib and tap it up and finally out. Had to smooth the gib and it wears a gouge to this day but it's worked ever since.It wasn't worn thin or i'd have replaced it.

You say your HANDLE is what lost teeth, not the internal gear(s) at the knee hoist? So all you need is a new handle?
 
I had a small screw get down into the gib space and lodge securely. I used my cherrypicker to unload the knee, removed the gib adjuster and and way wiper then with a combination of the machine's lifting handle and my hoist strapped around the table was able to hold the knee up and to the left enough that I could get in below the gib and tap it up and finally out. Had to smooth the gib and it wears a gouge to this day but it's worked ever since.It wasn't worn thin or i'd have replaced it.

You say your HANDLE is what lost teeth, not the internal gear(s) at the knee hoist? So all you need is a new handle?
 
I had a small screw get down into the gib space and lodge securely. I used my cherrypicker to unload the knee, removed the gib adjuster and and way wiper then with a combination of the machine's lifting handle and my hoist strapped around the table was able to hold the knee up and to the left enough that I could get in below the gib and tap it up and finally out. Had to smooth the gib and it wears a gouge to this day but it's worked ever since.It wasn't worn thin or i'd have replaced it.

You say your HANDLE is what lost teeth, not the internal gear(s) at the knee hoist? So all you need is a new handle?
 
Forrest has described the only real way to fix the knee.

Understand that the gib is acting as a wedge in the dovetail and that can be serious trouble. I hate it when I find a gib adjusting screw that has end play in the slot in the gib. That will cause trouble down the road by allowing the gib to move in and out as the knee or table is moved.

DO WHAT FORREST SAID.
 
Forrest has described the only real way to fix the knee.

Understand that the gib is acting as a wedge in the dovetail and that can be serious trouble. I hate it when I find a gib adjusting screw that has end play in the slot in the gib. That will cause trouble down the road by allowing the gib to move in and out as the knee or table is moved.

DO WHAT FORREST SAID.
 








 
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