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Knee hight adjustment screw tightness issue

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ZombiWelder

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#1
Gentlemen!
Kind of embarrassed to ask , must be something dumb and simple but I'm having issues with the acme screw on my mills knee. At some point it got a bit tight in some spots I assumed just chips got into threads. Some time after I went to clean the entire mill and after i cleaned everything the knee seemed to have gotten even tighter, about couple inches above the bottom of the travel . I thought must be some notorious chip that's below the nut at the base of the mill , so I strapped the knee to the head , and loosened the cone shaped lets call it "nut housing " and ran it up and down without any significant issues. Then I bolted it back down and knee got way tight. I'm assuming it's gotta have just the right alignment but my efforts to tap that nut housing into its happy place failed. It was late in the day so I figured I'll take a break, maybe ask some advice before I get back at her. Is there some clever trick to realign things? Am i 20181109_191549.jpg missing something?
Thanks a zillion!
 

tweinke

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#2
What brand / type mill do you have?
 

tweinke

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#4
just spit balling here, the main column hasn't shifted on the base causing the misalignment has it?
 

ZombiWelder

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#5
just spit balling here, the main column hasn't shifted on the base causing the misalignment has it?
Hmm,
Something too look at, thank you ! The mill is smothered in bondo, so would not be hard to see.
 

tweinke

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#6
I would think the Bondo may be your friend if it shows a crack where there was movement. Also another thought knee gibs in good order?
 

ZombiWelder

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#7
I would think the Bondo may be your friend if it shows a crack where there was movement. Also another thought knee gibs in good order?
It only one gib, I guess it won't hurt to check but turning the handle it felt like a binding screw
 

tweinke

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#8
I get what you are saying, hard to fix or help fix things when you cant touch or feel. I was hoping someone else would hop in here with a fix or idea also being I think 6x26 machines like yours are fairly popular
 

BaronJ

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#9
You do need to keep the knee sliding surfaces well lubricated !

However since you have run the nut up and down the screw, and its free, the binding can only be somewhere in the hight control mechanism. Since column alignment has been mentioned I assume that you have already checked that.

I'm guessing lack of lubrication or possibly a failing bearing in the gear at the top.
 

cathead

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#10
I would pull the gib and do some house cleaning on the ways, then reinstall gib with copious amounts of oil on ways and gib.
There is a positioner bolt on both ends of the gib to keep it tensioned properly(close to snug but with a little play). If the gib
slips deeper because the bolts are not tensioned correctly, the knee will surely bind.
 

BGHansen

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#11
Kind of winging it here, but how about taking the knee to the top of travel and blocking it with a wood block at the bottom. Remove the cap screws on the knee nut and spin it by hand up the screw. If it moves easily you're burr and chip free.

If that's the case, spin the nut back in place and loosely install the nut cap screws. Run the table down and watch the nut. If it shifts back and forth, the screw may be bent. You'd think it'd move in the same spot on the screw if that's the case.

With the knee blocked up, you could turn the crank and watch the screw and see if it's orbiting.

To check the table up/down on the ways, maybe use an engine hoist from above and slowly lift the table through it's range of travel. Look for hard spots on the way up or down.

Good luck!

Bruce
 

JimDawson

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#12
I don't think the problem is in the screw/nut system. That whole system is pretty loose and it would take a lot of misalignment to affect the operation. I'm going to suggest that the problem is in the gib adjustment.

My mill is tight both at the top and bottom. This actually improved somewhat when I tightened the gib.

I would try Bruce's suggestion of lifting and lowering the table with a hoist. I'll bet you will find some tight spots.
 

benmychree

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#13
I would be looking for galling in the ways, but a loose tapered gib could also be a culprit, it would likely run tight when going up, and loosen when going down.
 

Mitch Alsup

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#14
A couple of things:

a) the acme screw is supposed to be covered in grease...................
b) you can access the bottom of the acme thread by removing a panel under the base and clean it from there.
 

ZombiWelder

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#15
Thanks everyone for input!
I fingured it out! I apologize it looks like I haven't made my self clear enough. First thing I did as some suggested I loosened that nut on the bottom and ran it up and down and brushed the screw likely getting rid of some chip that caused problems in the firs place. The trouble was that nut housing thing had just one way of being bolted and sit perpendicular. No surprise there really , the mill got plenty of parts that have been finished by hand with an angle grinder or sit catiwampas.
 
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