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K&T 3CH Knee Gibb Covering

Mumf

Aluminum
Joined
Apr 11, 2009
Location
ontario canada
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My knee was moving approx 6 thou when i went from raising it to lowering it. I read many posts and tried to adjust the gibb. I could not get it below 3 thou when it started sticking and thus bumping on the way down. I removed the gibb. One side is clear metal but the side to the machine casting has what looks like a rubber coating. It is pretty flexible and soft like rubber. It also looks like it has been scraped. i do not want to rebuild the main body casting, so i am thinking of just putting it back. Anyone familiar with this type of coating?
 
That looks to me like flaking for oil, verse scraping to get flat. I assume that side is the non-moving or non-way side, is that right ?

If it is the way side, maybe it was supposed to be a version of turcite or the like, but I would not expect it to be soft. Maybe it succumbed to oil.

If it is the stationary side, I'd replaced it with metal shims, preferably brass or bronze.

If it is the moving side, I could think of a couple other options. One, make a replacement for the coating out of 932 bronze. Or maybe strip it off, allow metal to contact, but shim the non-moving side, assuming it, and gib adjuster can fit right.

If you have a straight edge, and any scraping skills might get it straight while you're at it, then adjust shim thickness to match. If not maybe you have other means to get it flat, or flatter.
 
It is the moving side- the one that makes contact with the machine part of the dovetail. I was thinking it may be, or have been, a type of turcite. I have never used it. I am not sure if it would soften with oil contact. I would have thought not, but.... i may strip it off and see what the metal surface is like.

tks
 
It is the moving side- the one that makes contact with the machine part of the dovetail. I was thinking it may be, or have been, a type of turcite. I have never used it. I am not sure if it would soften with oil contact. I would have thought not, but.... i may strip it off and see what the metal surface is like.

tks

I would not expect turcite or rulon to get soft. Could be someone was using "what they had".
 
Agree. strange thing is, it is soft and i can mark it with my finger nail, but it has little wear, except one small spot and a couple longer scratches.
 
Agree. strange thing is, it is soft and i can mark it with my finger nail, but it has little wear, except one small spot and a couple longer scratches.


Its also possible that you have some wear and will not be able to tighten, to let's say .001". Might get tight near top and bottom of travel. But I think you won't know until tightening proper, with a decent solid surface on gib.

Looking at page #40 of the parts book, I'm not seeing anything jumping out at me as far as the gib or its pieces:

Kearney & Trecker Co. - Publication Reprints - Model 3CH, 4CH Milling Machines - Parts Manual | VintageMachinery.org

The pdf:
http://vintagemachinery.org/pubs/2098/6524.pdf
 
That is Turcite for sure. I suspect the mill has been rebuilt/ reconditioned in years past. I wouldn't touch it! Leave it alone. If it's out of travel of gib adjustment, I'd do as Texas said, place a steel or brass shim on the back side of the gib. The shim can be pinned in place with a small piece of 1/8" brazing rod.
Keep in mind, if the gib has been fixed with Turcite, there's a very good chance that other surfaces of the knee have been reworked with Turcite, too. The "bumping" that is happening when the knee is lowered is from the slide surfaces "sticking" from gibs being too tight and or the lack of lubricant.
The 6 thousandths of indicator movement tells me knee is not "flat" on the ways that bear against the column. To fix this, you must rescrape the knee to the column to correct the "rocking" motion of the knee. Yeah, not a job anyone wants to do on a No. 3 mill. Really on that big old mill, that's not bad at all IMO.
Most mills, if checked, will show a little bit of movement on the knee, usually less than a couple of thousandths. That's why they say after cranking the knee down, crank up about a quarter to one turn to align the knee back up with the column. Yeah, it don't make sense but it works. Ken
 
thanks. i never knew turcite became soft. I think you may be right in that the machine column way is not totally flat. I tried to adjust the gibb a few time. As you say i may have to live with it. Not too bad in most cases. I noticed when boring the holes were not exactly eccentric. I will have to adjust the boring head so it does not cut on lowering the knee and thus cutting a slightly off center second hole. tks
 
just an update. I cleaned all i could and put it back together, oiling up etc. I am at about 1 1/2 thou when switching from raising to lowering. I am going to leave it like that and check that it is getting oil. thanks for he help.
 








 
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