Trouble lifting and lowering the knee

[5S Dude]

Are there any additional grease fitting or lubrication points on the “Elevating Screw” for a V2XT CNC Mill?

Thanks guys.

[gus]

I would be betting on gibs over screw if it is binding

[5S Dude]

Originally Posted by gus I would be betting on gibs over screw if it is binding

Thanks gus! There are what appears to be two small lock handles on the rear portion of the knee and I thought they were loose but I will check them out. Are there any other lube points besides the grease fittings.

[NEATman]

5S Dude-
If you find any additional lube points, let me know, as I've had an intermittend stick/slip condition when I lower the knee on my V2XT. It sticks, then drops - like a steady thump, thump, thump... Not good! It dosen't tend to do that when I crank it very slowly, only when I try to move it at a decent "knee handle cranking speed".

The vertical dovetails on my machine are well lubed as well, it has a one shot system, and the exposed dovetail shows a fresh oil film when I crank the knee up and down.

NEATman

[5S Dude]

Originally Posted by NEATman 5S Dude- If you find any additional lube points, let me know, as I've had an intermittend stick/slip condition when I lower the knee on my V2XT. It sticks, then drops - like a steady thump, thump, thump... Not good! It dosen't tend to do that when I crank it very slowly, only when I try to move it at a decent "knee handle cranking speed". The vertical dovetails on my machine are well lubed as well, it has a one shot system, and the exposed dovetail shows a fresh oil film when I crank the knee up and down. NEATman

Hi NEATman,

I did remove the three ¼-20 Allen bolts and remove the “Crank Shaft” and applied waterproof wheel bearing grease to the pinions and vertical jack screw through this access point. Once I removed the shaft it is easy to see into the knee casting. You can even lube the y-axis ball screw from this access point as well if the one shot poops out. Our mill also has a Bijur one shot lubrication pump located at the rear of the machine and in addition I have always made it a habit to squirt vactra 2 on the moving parts. We mainly use flood water soluble coolant on everything except tapping cycles and our machine typically runs on Saturdays only. Our knee started doing the same exact movement you described and Gus told me to check the two locking gibbs located at the locking levers where the knee mounts to the main body. They seemed to be working fine and I have started to think it may have something to do with the locking lever located just below the crank handle. I’ll have to fiddle around with it more when we return from the SEMA show next Saturday. Sorry for the dirty machine and that I couldn’t be of more help. I’ll try and add some photos of today’s tinkering. Have a great weekend.

[handlewanker]

Hi Dude, many years ago I had the same problem with a horizontal mill I worked on.
It got so bad that when you wound the table down it wouldn't move for the first turn of the handle, then a big thumpity thump as you continued winding down.

The boss got worried about it and had the machine stripped down and the knee removed to check.
The problem was caused by old lubricant, that had mixed with coolant trapped in the knee slideway and had decomposed to form a gummy varnish like coating on the slides and jibs, and caused so much stickiness that the weight of the knee was insufficient to overcome it, acted like a brake.

After a good clean up, no scraping required just degrease and relube, it was as smooth as new.
Oil does dry out, and the presence of water will also emulsify it and in addition there will be some corrosion that will make the surfaces rough.

The presence of rust between the slideway surfaces is in the form of a raised coating, and no amount of added lubrication will overcome it.
One of the big problems with sliding metal on metal slideways is if there is insufficient movement on a regular basis, then corrosion WILL take place.

A while back there was a big discussion on this forum with someone with a knee on a Bridgeport that had frozen solid and needed dynamite to move it.
It's a massive job to dissasemble the knee from a mill, to just clean it out, but if it's not done then the slide ways will get corroded.
Needs some very heavy lifting tackle, unless you take the table and crosslide off first, big job.
Ian.

[chich2]

How about try a high detergent oil through it for a while? This will break down any varnish quite quickly.

Chich

[5S Dude]

Boy! I’d hate to have to take the table and knee unit off the machine to clean the vertical ways. By looking at them they do not appear to have any corrosion present. I will look into high detergent oil and some sort of degreaser to see if this helps. This forum and you folks are quite simply awesome. Thank you so much for your input.

[NC Cams]

First of all "detergent" oil contains disperants which HOLD stuff in suspension/solution do that it is flushed out when the oil is changed. It is not a "washing detergent" per se.

Moreover, part of the additive package that is a part of "detergent oil" (namely the zinc anti wear additives) literally etch and plate themselves to the iron/steel particles. Depending on the metal, this can be detrimental to the integrity of the parts, especially if it mixes with water and/or cutting fluids. More on this later

Coked/caked and/or dried out lube is nasty stuff that needs an appropriate solvent to break up/down in order to re-liquify it - "detergent oil" may not be that solvent.

Some solvents to consider would be WD-40, othe "penetrating oils" and perhaps Dexron. These all have demonstrated a capability to disolve and/or penetrate oxydized lubes - they may not work with concrete solid caked on lube but may/should work better than "detergent" oils.

Guys have used various home brew concoctions to disolve tired/caked/oxydized grease. You really need to be careful both from a health/safety standpoint as well as from a compatibility standpoint.

Reason: the BPT's uses bronze gears and bushings and ball nuts. These can readily be attacked by the additives in some lubricants - the Zinc anti wear agent in "motor oil", expecially "detergent" oil is not particularly friendly to some bronzes - Why? Zinc bonds with and attacks the copper in bronze causing it to break down and lose structural integrity.

Dexron, however, if formulated to be bronze friendly - Why? Because a lot of tranny thrust washers are bronze based and the lube/additive formulation is made in such a way to NOT be agressive toward white or cuprous metal bearings. A simple tranny fluid change has been known to unstick gummed up valve bodies in auto transmissions - it may do the same for solidified grease on the knee.

A trick that can be used for gummed up hydraulic valve lifters is to give the engine a dose of couple of quarts of Dexron along with the regular oil - allow to idle for 10 min or so and drain while the oil is HOT - DO NOT DRIVE.

I've seen where this trick will quite down gummed up lifters and even free up stuck/gummed up oil rings. You do NOT want to run it straight as it does not have the anti-wear additives that are needed for non-roller tappets. This is why you have to dilute it with "real" motor oil. The commercial "motor flushes" may be helpful in disolving gummed up varnish and lube as that's what they are designed to do/meant for.

Talk about real "detergent" package, motor flush is it....

[chich2]

Thanks for the info NC Cams. Sorry for the bum steer I guess. The reason I stated this is due to a problem we had in a 3 stage turbo compressor at work. Beautiful machine. It's an air compressor that produces 5000 cu/ft a minute at around 800kpa (120psi) 1st stage is approx 9" dia spinning at 25,000 rpm and stage 2 and 3 are progressively smaller both spinning at 36,000 rpm. Any way the gear train and hydrostatic bearings got deposited with a varnish or shelac all over the gears and shaft. It was recomended by the manufactruer to run a "high detergent oil" to remove this gunk. But going from your information it looks like the oil recomended by the manufacturer to do this with probably contained something else in it that did the actual cleaning. The "Detergent" may have been a figure of speach?

Thanks for the info,
Chich

[NEATman]

Wow!
Thanks for all of the ideas everyone! It sounds as if I have a bit of work to do on my machine. Luckily, the knee is the only axis that has this problem. I'll try cranking it to it's extremes of travel, and cleaning the exposed dovetail areas that I can see on the base, and perhaps that will reduce the problem.
Otherwise, I guess I'll need to pull the knee off, and get it clean. I'll be sure to clean out all of the one shot lines and orifices when I'm in there. I've been meaning to purchase a 2 ton shop crane for a while now. This will be one of the first tasks for it.

I've also been wanting to measure the underside of the knee and the knee screw for a while now, as I have what I think is an original idea on retrofitting a knee mill to drive the knee.

NEATman

[cut more]

Hi guys,
We have a manual bridgeport at work that has the same issue when lowering the knee. I have found on that mill, if you tighten the knee lock the stick slip goes away. This is not the cure, merely I think an indication of the knee gibs on this machine needing to be re adjusted. Any one else agree or dis -agree?
Maybe a couple others with this problem could try it and see if you get the same results.
I had to tighten the lock snug not cranked down.

Cutmore