Adjusting Jib on Knee

[Kroll]

Guys I know that you tighten the screw little which pushes the jib down which acts like a wedge.But when you have a crank thats has a handle thats about 18" long you can really do some cranking.So how can I tell when I have the jib for the knee adjusted just right?

 

[Technical Ted]

That's a good question... and I'm not sure I do it correctly, but this is what I do on my Bridgeport.

I put a dial indicator on the table so I can see vertical movement. I tighten the gib up making sure there is no drag when I'm going up (just snug it a little). I lock the knee lock and back the screw off (turn counter clockwise on the hand crank to lower), but only move it within the nut's backlash. The lock should hold the knee and you should not see movement on the indicator. Then I remove the lock and you should see the table drop some amount (again, within the backlash of the vertical nut).

Now, I tighten the gib up enough to see this same holding action by over tightening the gib. And then, back off on the gib adjustment to a point where it drops freely with the turning of the crank.

So, I tighten it to the point of holding the knee (like the lock does) and then back off until it doesn't.

Of course, you have to remember that depending on the wear in your ways this could vary depending on the knee's position.

Not sure if this is the best way, but it's how I do it.

YMMV,
Ted

 

[JimDawson]

There is a screw on the bottom also. You have to tighten one and loosen the other. Tightening the top one tightens the gib. Once you are happy with the way it feels, tighten the bottom screw.

I just adjusted mine by feel, when it felt right up and down I quit tightening.

 

[benmychree]

It should be tight enough to eliminate play, but loose enough that the knee does not stick when being cranked downwards, suddenly dropping when slack is taken up; its a fine line!