Author Topic: Knee movement on the Mill  (Read 6678 times)

ddickey

Knee movement on the Mill
« on: July 08, 2018, 06:01:20 PM »
How much movement is acceptable (seen at the vise) when locking the knee?
Thanks


4GSR

Re: Knee movement on the Mill
« Reply #1 on: July 08, 2018, 06:34:36 PM »
I assume you are talking about movement on your indicator?

On a new mill, zero.  A worn out mill, well, what can you live with?

I had a 1910 vintage B & S mill when I was younger.  We scraped out the middle on the knee before we re-installed it, knowing it had wear.  Got about .001" indicator movement at the knee, about .006" at the vise.  We lived with it.  We just made sure the slack was taken up in the knee when moved.

Ken
Ken

Bill Gruby

Re: Knee movement on the Mill
« Reply #2 on: July 08, 2018, 07:08:58 PM »
 As Ken said, how much can you live with???

 "Billy G"
I'm pretty sure that my last words will be, OH SHIT,THAT DIDN'T WORK.

Uglydog

Re: Knee movement on the Mill
« Reply #3 on: July 08, 2018, 07:22:41 PM »
You might find that there is more movement in the middle, top or bottom.
Supposedly most manufactures scraped them to lean in at the top so that as they wore they became level.
I'm guessing you've already adjusted your gibs. This can get tricky as then using the other parts of the knee where there might be less wear might bind.
You might try tackier way oil to buy you more time on a rebuild. But the down side is that it might plug up your oiler and oil grooves, especially if they are already loaded.

Daryl
MN

4GSR

Re: Knee movement on the Mill
« Reply #4 on: July 08, 2018, 10:01:43 PM »
I've very seldom seen a Bridgeport mill or it's clones have noticeable wear due to its fairly balanced knee because of the location of the elevating screw.  Over time, they do get out of adjustment and require adjusting.  But if neglected over the years from the lack of adjustment or someone f!cking with the factory adjustment, you will get excessive wear! 

I don't claim to be an expert at this, just seen the results of wear and tear on machine tool members over the years.

Ken
Ken

gtermini

Re: Knee movement on the Mill
« Reply #5 on: July 09, 2018, 12:18:02 PM »
The trick is expecting the movement. Creep up on your number and lock the gib right as you come up. Easy with a dro or dial indicator mounted on the column; a little trickier without. I have never trusted the knee on a BP for depth cuts. After cranking down, I've made it a habit to put a half turn up on the knee to take any slop up. I have a 2 year old professionally rebuilt BP at work with a dro on the knee, and there's about 20 thou before the knee starts moving either way when you crank.

I have seen BP chicom knockoff slump over on the column. When they originally copied one, they for got to but some internal bracing in the body to prevent this. Ask any rebuilder, and they say the BP's with the door in the side are better castings because Textron did the same things china did on the knockoffs.

Greyson

ddickey

Re: Knee movement on the Mill
« Reply #6 on: July 09, 2018, 03:16:27 PM »
I'll have to do some more checks on the movement. It's a new Taiwan made PM mill. I need to check the gibs. I guess my assumption was they were properly adjusted since it is new. I noticed it when tramming in the head when I lock the knee the table would move relative to the spindle.