Need Help!- Broken Knee / Column Gib-Strip

[niggle]

Purchased a bridgeport mill as a plan to fix it up. The Gib-strip between the knee / column has broken around the adjustment screw, and because of it's tapered design has locked the knee and column up quite well.

We did believe that the knee is was at the bottom of it's travel, but have since un-bolted the 'z-axis leadscrew nut bracket thing' that bolts to the base, and it should have around 1" until the bottom of it's travel.

How to free it???


An initial idea (as there was a small peice of gib-strip underneath) was to lever it up with a big bar. Didn't even move a thou!

Next idea.. Support the bottom of gib-strip with packers, and force knee down with ratchet tie-downs. Nope, no movement again. Now tryed 'swinging-press' techinique. (Sledge hammer). No movment.

Now tried drilling and tapping the top of the gib-strip 1/4 UNC, but broke side of gib-strip out. had to tap it at an angle so I could get the drill in there, but have now thought that I could possibly weld a short length of bar to the tap and drill bit to drill colinear with the gib-strip. Would use a thread around 5/16 or M8 next time.

Next idea which we thought would be perfect, was to lay the mill on it's side, drill through the base, and hit the gib strip out with a long punch. Nope, not going to happen. There's a huge cast rib running right along behind and under the dovetail (in the coolant sump).

We're about to get hold of a mini 4 ton hydraulic ram, and try push the gib-strip up from the bottom, Hopefully this works.


Has anyone else been in this situation? Would like to know some more possible solutions if the hydraulic ram doesn't work!


Details from mill:

Serial Number 9548-M
Order Number 39018
12/69 (Manufacture Date?)



Thanks heaps.

Nigel,
New Zealand.

[abarnsley]

http://www.cnczone.com/vb...ort+stuck+knee

[gridley51]

Nigel,you are in deep s***.The wrong step now will crack the knee casting and the machine will be scrap.You do not have many chances left so what you do will have to be well thought out and done correctly.That means no hammering with whatever punch comes to hand or half hearted drilling and tapping holes.As the machine is so far down the slides you do not have a lot of options.First thing is to get some release oil in there.It won`t free it but every bit helps.Give it a few days to get in there.Personally I would make up a stop slightly smaller than the small end of the gib and screw and pin it to the slide to stop the gib moving any further down.Then either the big hammer or a jack to force the knee off the gib as far as you can.I know it`s only an 1" or so but every little helps.If and when you can get the knee off the gib as much as you can you then have to try and find a way of anchoring the gib to the knee so that you can jack the knee back up the slide without the gib tightening.A way of doing this is to drill through the casting and gib and put like a 12mm dowel in the hole.When you are sure the gib is anchored try jacking the knee up the column,be careful with the force or you will crack the base.If this is successful then make a longer stop for the bottom end of the gib and force the knee down again and repeat.If this does not work you`re only other option is to put a hole through the base and get a punch in there.The punch has to be as near the size of the gib as possible and it will need a big hit,not small hits as they will only spread the gib and make your problem worse.
Best of luck.

Mark.

[Cartesian-xyz]

Niggle
I had the same problem on a BP mill I bought. I did almost everthing you tried and came to a dead end...The gib would not MOVE!!. As a last ditch effort of Fix or Failure
I cobbled together some support under the knee to keep the gib from moving down any further. I then took a 5 ton bottle jack and set it as close to the column as I could and begain applying pressure between the table top and Ram.... After way more than I would have imagined for pressure it BROKE FREE!! i then used a flexable rod to remove broken gib. After all said and done it did not appear to damage anything on my BP. And mine is a 1956 vintage round ram design. If yours is the dovetail ram then I believe it would withstand even more abuse.
I have been useing mine after repair for 2 yrs now. No problems!
Let me how it goes.
Stephen

[WALloyd]

I am a professional rebuilder and have seen this problem many times. The way I remove them is to lay the B/P on its back, drill a hole through the base so a drift will pass through and the gib can be struck. One or two sharp blows and out it will come. Don't be afraid to hit it. good luck.