Knee Gib Removal
The phone rings. "H & W Machine Repair, this is Barry, can I help you?"
It always begins the same. "Good morning Barry, this is Doug at XYZ and the knee on my mill is stuck, I can't get it back up."
This is like having a root canal and a colonoscopy on the same day. 99 out of 100 times the problem is the 18" adjusting gib between the knee and the column. The root cause of this problem is a lack of lubrication. That may be because the lubrication system is not being pumped as often as it should be or because the oil meter, a $12.64, item is plugged and not allowing way oil to get to the gib. Whatever the problem, you don't want it.
Don't let it happen in the first place. The one shot lubricator on most mills needs to be pumped at least once a day. (I'm assuming here you use your mill every day) However, it never hurts to make sure oil is being delivered to the ways. The easy way to do that is, raise the knee up near the top and pump the lubricator a couple of times. Come back in an hour and see if oil is running down the column ways. If it is, you're in good shape. If it's not, you need an immediate answer to the question - why not? It could be the one shot lubricator isn't working properly, the oil meter is plugged at the distribution manifold or the oil line may be crimped or plugged. But first, before something really goes wrong .........
Z Axis Gib Adjustment
Z Axis Gib Adjustment
Remove the covers and the way wipers on the top of the knee. This will expose the gib and the gib adjusting screw. Flood this area and the other side with way oil and go have a coke or a cup of coffee. Come back in an hour and see if the oil has worked its way to the bottom of the column way surface. If it has, you are a lucky man. You still need to find out why it's not getting there from the one shot pump but that is not so hard. If the oil is still standing at the top, you are on the cusp of a real problem.
The first thing you need to do is put some blocks under the knee, then lower it until it is supported by the blocks. This is done to take the weight and pressure off the gib. Next, very, very carefully, "try" to loosen the gib adjusting screw with a straight bladed screwdriver. Please, be very careful doing this. If you try too hard, you can easily break the tang off the gib and if you do, you are really in a world of hurts. If you can loosen the screw, do so, then flood the area again with way oil. Next, raise the knee, remove the supporting blocks. With those out of the way, lower the knee, completely remove the gib and clean it.
What if the knee is stuck? DO NOT LOWER THE KNEE! Step number 1. Remove the way wiper covers and the way wipers. Flood the area with Penetrating Oil and let it stand. While you're waiting, find a piece of flat stock or some type of tool that you can slide up behind the knee and make contact with the bottom of the gib. Step number 2. You've got to get the load off the knee. If you have a small bottle jack, get it and put it under the knee. Put slings under the table and raise it with an overhead crane or you can even use a fork truck but you've got to get that weight off the knee. Step number 3. While someone is tapping on the gib from the bottom, "very carefully", try backing out the gib adjustment screw. Hopefully, this will be the end of your problem.
Broken Z-Axis Gib
OK, worst condition, the tang on the gib is broken and you've lowered the knee all the way to the bottom. Disconnect the electricity to the mill. Remove the Head, Ram and the turret from the column. Removing these pieces takes time and labor, but removing them prevents a lot of potential damage should something go wrong with what I am about to suggest. "
Very carefully", tip the mill backwards so the column is laying horizontality. Drill a 1" hole in the base of the column as you see in the picture below. Take a bar or a rod, machine it or grind it down so that it will slide up into space between the knee and the column and touch the gib. If the tang is broken, the gib may be protruding out the bottom. With your tool against the bottom of the gib, HIT IT! Hit it hard and with enthusiasm. You have to knock that gib loose. If it doesn't come loose when you hit it, HIT IT AGAIN! There is no tomorrow, the cavalry is not coming, this is it, do or die.
Z-Axis Gib Mark And now, a word of encouragement. A number of times, we have had to resort to this barbaric tactic for customers in their shop. Only once have we failed to get the gib out. Sometimes it comes out and can be used again. Most likely you will have to do some grinding on the bottom of the gib where you buggered it up. Be warned though, sometimes it comes out in pieces so be prepared to replace the gib.
Remember, all this can be prevented if the lubrication system and all the delivery parts and pieces are working properly. Take the time to make sure it's all working.
