Stuck Knee Gib



Here's the story. Click on any photo to see a larger version.

When I acquired this mill, the knee crank was missing. I didn't think much about it....just figured I'd have to buy one on eBay. I knew I was going to be buying some parts to get it back in working shape.

After spending time at the car wash (yes, the car wash and $20 worth of quarters) cleaning the 20+ years of grime and chips off of it, I discovered that someone had turned the knee crank so hard that they split the "Gear Shaft Clutch Insert". By this time there was no going back. I found that the knee/column gib had broken at the slot and slipped down, wedging it deeper into the knee column

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Gib below dovetail  Removal of gib screw         Showing broken slot on top of gib

After searching the forums for other occurrences of broken knee/column gibs, I ran into all kinds of horror stories.

I finally settled on the story that Forest Addy told in 2007 on the Practical Machinist website.

Maybe it's the anal retentiveness of believing that careful planning and preparation almost always comes out good.....or the superstition that if I try to short cut the procedure and fail, I'll be kicking myself in the butt (done it many times) because I didn't want to take the time to do the job properly. In any case, this procedure is the one I chose and I'll make the effort to follow it and see if I can save the mill.

On another note, I am a believer of having the correct tools for a job. Many times I am lucky to have a proper tool for a unique job and other times its that I insist on having good tools so over the years, I buy them. I also am lucky enough to have all the materials to make the fixtures that Forest suggests. (i.e. 1/2" and 3/4" plate and the means to cut them). Makes me feel pretty good that all this collecting of materials pays off at least once.

One thing I did not count on was my brother picking up a very nice magnetic drill press from a local pawn shop and I absconded it before he turns around and sells it. It saved me a ton of time not having to maneuver the 3/4" and 1/2" plate on my drill press.

First order of business is to make the fixtures to secure the knee from moving while attempting to removing the gib. This turret plate will also serve to help stabilize the mill once I figure out how to roll it over on it's back.

Here I am laying out the 24" x 24" 3/4 plate for turret plate and using the magnetic drill to make the 9/16" holes. This drill is really cool....and quick.

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This plate extends over the front of the mill and column ways as well as extends over the back of the mill.

Next I set up to cut the 1/2" plate that will go over the column ways and secure the knee from moving once the gib is tapped on. I drilled corner holes and then hand plasma cut (even though my CNC plasma gantry was in the background....I just didn't want to hook it up for such a small cut).

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Then I placed the thin cardboard on the ways on both side of the column ways so that I don't damage them when I place the plate on it. I also split some plastic hose and placed over the inside of the 1/2" plate to protect the column ways. Plate is in place.

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Top plate is bolted in place and now to measure how much I need to trim the front plate.

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I need to take off about 0.060 to 0.070" to make it flush.....wonder if I can get my band saw to cooperate.

This band saw (Grizzly) is not the most accurate one in the world but I have been able (by taking time to set up and cut very slowly) to slice off some pretty thin slices on big plates. I maxed out the jaws to hold the 12" plate and then went about taking off about 0.070" (0.035" slice and 0.035 kerf). A little hard to see but the saw is slicing very thin stuff.

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First pic is the slice.....second is the blade (kerf)....still getting lucky.

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So now the 1/2" plate is flush with the 3/4" plate......enough to hold the knee when whacking on the gib.

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Now I'm going to drill a couple of holes to mount these boards so that when I lay the mill over, it will be stable and not try to roll on it's side.

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More to follow tomorrow as we lower the BP on its back and bore the hole in the base getting ready to carefully whack the broken gib out.

Time to clean up because it's supposed to rain tonight.

20:10 1/22/2007


Saturday, 1-23-2010 09:00

Note: Bear with me on this story as the plot will change or, at least the method will....

The phone rang at just after 9am. I had been up late the night before getting everything covered up because it was supposed to rain a bit. I'm working outside under a large canopy, but any rain can get under the canopy and make a bigger mess than I already have. I had just gotten up and poured a cup of coffee and settled to read the morning paper. Actually the "read the paper" is just an excuse to give me time to wake up. The older I get, the longer it takes to get functioning. Anyway, back to the phone ringing......

It was my good friend Bob Campbell ( Seems he sent this link to a buddy of his last night and the buddy just happened to drop by Bob's house this morning and told Bob he had removed gibs like this before and wanted to come over (Bob only lives a few miles away) and talk to me and see what I had. Bob insisted that this guy knew "everything there was to know about Bridgeports" and that I should listen to him.

Those that know me know I (most times) am a methodical (i.e. anal type) guy. I usually research a problem, choose (or create) a solution, proceed with that solution and many times document it as I go. My ego says I would say that I document it because I want to help others who may find themselves in a similar situation, and I do, but full truth be known, I am apt to find myself in this situation again and will forget how I fixed it the last time. So there...the truth is out.

At this point I am not usually open to new options. Mainly because many times in the past when I have not "stayed the course", and deviated away from a well thought out procedure, I have lived to regret it. Today was no different. I decided to tell Bob to come over in an hour and bring his friend with him and I'd listen. I didn't expect to change my mind. I had already decided on the "Forest Addy Procedure" (sounds like a surgical term). Though long in setup (Forest even warned us of this), it had produced good results for him...and I was convinced that if I tried to cut corners.....I'd regret it.

At about 10am, Bob showed up and introduced me to Bill Nelson. Bill and I talked for a bit and I learned that he owned his own tool and die business for many years. He'd worked as a tool and die man for a great many years before that. He brought photos of some of the mills he had restored to working shape they made mine look like it came off the Bridgeport showroom floor. Some were rusted almost beyond recognition and were literally laying out in a field.

I showed Bill my mill and explained the "Forest Addy Procedure", the long prep work I had already performed short of tilting the mill on its back and carefully whacking the gib out. He listened and offered to help me do whatever procedure I had decided on to help me get the gib out. To be polite, I asked him what he did in situations like this......assuring myself that I was "staying the course".....

Bill said since my gib was sticking out the bottom of the knee 1/2 to 3/4", that he would cut a piece of steel to put between the end of the gib and the base of the mill. This would immobilize the gib just like I had immobilized the knee with the two plates. Since I had not yet removed the knee screw, we would loosen it up s that it would not be holding the knee up. Next we would put 2 oak blocks on the chrome ways of the knee and a steel plate across the knee on the blocks. A hydraulic ram would be placed on the plate and the ram extended to the turret plate I had earlier installed. Once we had some good tension on the ram between the turret plate and the knee, we would give the turret plate a couple of good whacks on the top to give the final shock to the stuck gib and the knee would drop......stopping on the knee screw and the large piece of steel that had been immobilizing the gib. If that didn't seem to work, we'd follow through with the "Forest Addy Procedure".

Bill's reasoning for his procedure over the Addy one was that when we smacked the bar that was driving out the gib in the Addy procedure, we were forcing the gib past 2 surfaces (on each side of the gib). If we used the procedure he suggested, we were only forcing the gib past the surface on the knee dovetail....since the gib was immobilized and stayed with the column dovetail. Now to be honest, my brother and I had discussed this option a couple of days ago but had not seen anyone on the any of the forums use this hypothesis (maybe I just missed it...and I'm sure someone will point that out) and I was looking for procedures that someone had actually been successful with.

Now the fact that Bill offered to help me with whatever method I wanted to perform said that he was not going to push "his" way as being the best....only that our end goal was to relieve the mill of it's knee/column a safe manner. I liked Bill.

Bill had to drive Bob home and said he'd be back and I could decide whatever I wanted to do and he would be glad to help. While he was gone, I toyed with Bill's idea. I cut a piece of 1/2"x3/4" bar.....ground one end to fit the curve of the base of the mill directly under the gib.....just in case I wanted to "sway" from the course a little.....wire brushed down to the metal of the base (through 3 layers of paint and "bondo"....and tapped it in below

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So good so far......then I cut 2 oak blocks to lay on each side of the knee ways...covered them with the leftover 1/2" plate I cut out of the upright "knee to turret" plate for the "Addy Procedure"...and put a few folded sheets of paper behind it to protect the column ways.

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No harm so far. Bill returned and I told him what I did. We released and raised the knee "nut" on the knee screw about 3/8" just to give us some clearance if the new procedure worked...(swaying from the course a little). This is looking inside at the knee screw

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So we put the ram between the plates and inched it up....and up....and up...and the knee didn't budge. Looking at the turret plate where the ram encountered it, we saw a little gap of sky come just under the turret plate to the mill column top (plate was giving a little.....maybe 25 thou) and figured if we "rammed" any more and we would break the turret bolts or the spider casting. (Yes, I know it is in very bad form to use vise grips on the knee crank, but someone had already beaten me to it and buggered up the shaft already after they split the knee crank nut while trying to move the knee with the stuck gib so I figured I couldn't do it any more harm. I'll either clean it up or replace the shaft.)

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We decided to give the top of the turret plate a max of 3 whacks with the sledge and if that didn't work, we'd lay it on its back and, once again, "stay the course".

On the 3rd whack the gib "gave up the ghost" and freed up. The knee dropped the 3/8" we had loosened the knee screw. At this point I tapped out the steel bar that had immobilized the gib....and replaced it with a thin piece that would follow the gib up into the knee way as we lowered the knee. Thin piece (1" x 0.125" pic below.

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After lowering the knee, the gib came out the top and it looks like this....

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It looks like it is chromed....I didn't know that.....and it looks like it has a serial number....I didn't know that either...........AND...

I just found out from Bill that when I buy a new will have to be fitted....and oils grooves made...and scraped and flaked........ AND I REALLY didn't know that.........but....

Bill says he's done all of that several times.....and you know what....I believe him!.

He offered to help me with fitting the new gib when I get ready to put it all back together.

I made a new friend today. He's "been there, done that"...and doesn't mind helping others to do the same........that's the kind of friend I want (and want to be)....and I've got good friends like Bob Campbell who look out for spite of myself.

Randy 19:46 1-23-2010

BTW, the "Addy Procedure" will always be the backup plan.....but the "Nelson Procedure" is the one I'll start with....pending I ever get in this pickle again

(Now that I've documented this adventure, I'm sure there will be discussion of it on the forum(s). The guys who used the "lever/fulcrum" methods and made them work are more sure of themselves than I was of my abilities. My hat is off to them. The guys like Forest Addy and Bill Nelson who help others in a bad situation like I was, my hat is off to them as well. In fact, I may never wear a hat again....shows off my bald head. My brother, Terry, is always coming up with much needed (or desired) unique tools that make many things much the hydraulic ram, the air powered "cherry picker", and the magnetic drill/hole saw........many thanks to him for all the physical, mechanical, and moral support....not to mention the myriad of "sanity checks" we have.....he IS heavy, but he's my brother!

Now on to getting this hunk of iron back in production.


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