Kiwa Excel 510 : Z axis ballnut seized!

Kiwa Excel 510

The machine was sitting outside for about 10 months. I had it under a tarp, but I had the Z motor taken off.

A few days ago I decided to bring the machine inside and begin its TLC process. When I had shut it down 10 months ago X, Y, and Z axis jogged fine.

Now the Z axis ballscrew wont move. I have the motor off and thrust bearings loose (they turn). So basically I have just the ballscrew and its nut so its isolated to those things. The machine has a counterweight so I am 99% sure there is no brake buried somewhere in the lower casting.

The ballscrew is very difficult to turn by hand. I have to grip it with a towel and twist hard and it moves but its very notchy and I dont think I should be doing that.

Two things I noticed:

a) inexplicably the lube lines had water in them!! I am not sure how that happened. There is no obvious way for water to get in there except going backwards through the lines from outside, due to condensation or splashing from rain under the tarp?

b) X and Y axis work okay

So..I guess rust is the issue here. What can I do? I like this machine and want to fix it. I've pumped PB blaster directly into what I think is the ballnut lube tube and I've sprayed the chip guard on the top of the ballnut with plenty of PB blaster and WD40.

I'd like to get the ballnut/screw out but from the looks of it I guess I would have to remove the head? This ways are square. I do have a cherry picker handy and in theory I should be able to come up with a way to safely manipulate the head in the air.

I'm not actually sure how the head comes off. These are box ways (square?) and I guess you actually unbolt sections of the head casting that grab the ways? I'm not familiar.

Any help greatly appreciated!

Also been thinking of hooking up a pump with evaporust and pumping it continuously through the ballnut but not sure how I would catch it on the output...

laggeddag said:

Kiwa Excel 510

The machine was sitting outside for about 10 months. I had it under a tarp, but I had the Z motor taken off.

A few days ago I decided to bring the machine inside and begin its TLC process. When I had shut it down 10 months ago X, Y, and Z axis jogged fine.

Now the Z axis ballscrew wont move. I have the motor off and thrust bearings loose (they turn). So basically I have just the ballscrew and its nut so its isolated to those things. The machine has a counterweight so I am 99% sure there is no brake buried somewhere in the lower casting.

The ballscrew is very difficult to turn by hand. I have to grip it with a towel and twist hard and it moves but its very notchy and I dont think I should be doing that.

Two things I noticed:

a) inexplicably the lube lines had water in them!! I am not sure how that happened. There is no obvious way for water to get in there except going backwards through the lines from outside, due to condensation or splashing from rain under the tarp?

b) X and Y axis work okay

So..I guess rust is the issue here. What can I do? I like this machine and want to fix it. I've pumped PB blaster directly into what I think is the ballnut lube tube and I've sprayed the chip guard on the top of the ballnut with plenty of PB blaster and WD40.

I'd like to get the ballnut/screw out but from the looks of it I guess I would have to remove the head? This ways are square. I do have a cherry picker handy and in theory I should be able to come up with a way to safely manipulate the head in the air.

I'm not actually sure how the head comes off. These are box ways (square?) and I guess you actually unbolt sections of the head casting that grab the ways? I'm not familiar.

Any help greatly appreciated!

Click to expand...

I’m sure people far smarter and wiser than me will chime in.
What do you mean by removing the head?
The spindle motor and spindle assembly?
The whole Z axis column?
I wouldn’t trust a cherry-picker for that...
The Z column is likely bolted to the base casting.
I would use a gantry or A frame to securely lift/lower either the spindle or the Z column.

laggeddag said:

Also been thinking of hooking up a pump with evaporust and pumping it continuously through the ballnut but not sure how I would catch it on the output...

Click to expand...

I would definitely NOT do that!
I would pump kerosene+oil through it, or diesel or something, but definitely not Evaporust.

rpseguin said:

I’m sure people far smarter and wiser than me will chime in.
What do you mean by removing the head?
The spindle motor and spindle assembly?
The whole Z axis column?
I wouldn’t trust a cherry-picker for that...
The Z column is likely bolted to the base casting.
I would use a gantry or A frame to securely lift/lower either the spindle or the Z column.




I would definitely NOT do that!
I would pump kerosene+oil through it, or diesel or something, but definitely not Evaporust.

Click to expand...

Okay and I assume that means also dont soak the ballnut or any of its components in evaporust if I get them out? Because high-carbon right?

For removing the head I mean my goal is to get the ballscrew and ballnut out of the machine so I can either somehow fix the ballnut or replace both. I think based on how the machine is constructed that I need to take the head casting off (not the Z column). I have not done this before with box ways, it appears to me the head casting attaches to the ways with large blocks of cast iron that are bolted to the head casting, thus "pinching" the ways. Does that sound right?

I've only worked on one other VMC before and it was dovetail so this is new to me.

So I think this section of the head casting actually unbolts (on both sides) and then the head casting is essentially free to move away from the Z casting..correct?

If I take the spindle motor off the head casting should only be a few hundred pounds. A cherry picker should be able to get its ram over it and manipulate it pretty easily. I would have to lower it enough for the stuck ballscrew to clear the z column, then back up and pull it away enough to be able to get the ball nut off.

Does all this make sense? I really made an effort to find "removing head with box ways" threads but google completely failed me. I see nothing. I know people must have asked about this but I just cant find anything.

And I am not too heartbroken about doing this. I need to get familiar with this machine anyway, and really the thrust bearings and/or the ballscrew might be something I would have replaced anyway. But now I just need to get it out of there. Will give me a good chance to clean things as well.

UPDATE

I just went out to the machine and tried turning the ballscrew again. Its much easier! I think the PB blaster injected into it has done some work. The thing is I know there must be rust particles in the ballnut and it doesnt feel perfectly smooth, its just much better than before. Should I "flush" it and if so how do I do that? Would fluid injected into it (like suggested) actually take particles with it on the way out? (How does oil get out of the ball nut anyway, isnt it a tight fitting seal that might hold particles back?)

Or should I just proceed with taking the head/ballnut off so I can take everything apart and clean the inside of the ballnut and all the balls?

laggeddag said:

Or should I just proceed with taking the head/ballnut off so I can take everything apart and clean the inside of the ballnut and all the balls?

Click to expand...

This, but be damn sure you have all the heavy items are properly secured so you don't get hurt.

Check, check again, make sure someone else is around when you're in/on the machine.

Milland said:

This, but be damn sure you have all the heavy items are properly secured so you don't get hurt.

Check, check again, make sure someone else is around when you're in/on the machine.

Click to expand...

Is there a logic to when the ballnut should be taken apart and when its better to leave it together? I've seen some conflicting advice on here...

Ballscrew cleaning.......take it all apart?

It seems like some people (including ballscrew refurb places) think its not that big of a deal to take it apart as long as you use standard amounts of caution and prep the area to catch any balls that might get loose.

So is flushing the ballnut not a realistic thing?

laggeddag said:

Is there a logic to when the ballnut should be taken apart and when its better to leave it together? I've seen some conflicting advice on here...

Ballscrew cleaning.......take it all apart?

It seems like some people (including ballscrew refurb places) think its not that big of a deal to take it apart as long as you use standard amounts of caution and prep the area to catch any balls that might get loose.

So is flushing the ballnut not a realistic thing?

Click to expand...

Trying to flush the ballnut is much quicker and easier since you said you have access to the oiler lines.
You can always take it apart later if flushing doesn’t work. Taking ballscrew out and ballnut apart is a lot more work.

rpseguin said:

Trying to flush the ballnut is much quicker and easier since you said you have access to the oiler lines.
You can always take it apart later if flushing doesn’t work. Taking ballscrew out and ballnut apart is a lot more work.

Click to expand...

Okay I'm going to try this then. I have VM&P Naptha. Heres my plan:

-Clean ballscrew as much as I can on the machine..get all chips off it, then use steel wool and or scotch bright to take off any surface rust. Combine with simple green and so forth to degrease. Do this on the top and the bottom of the screw. (top is easier..not sure how I will get to bottom, I will have to remove access panel I guess).

-Inject ballnut lube line with some kind of solution of a solvent and a lube. Probably alot like 100ccs or more. I dont have any kerosene or diesel. I do have VM&P naptha. Can I mix some vactra into that and inject that? Dont want to inject a straight solvent right? Or should I just pickup some kerosene and mix it with vactra? Edit: probably move the ballscrew as I am injecting to really help the flush.

-Wait several hours. Then inject some lube and twist the ballscrew a few times to loosen things up and see how its going.

-Repeat the injection cycle probably at least once but maybe more. Try to get the screw to move as much as possible.

-Regrease the thrust bearings since I totally wiped them out with PB blaster and WD40 when I thought they were seized.

-Put everything back together and start 'er up!!

Before I invested all that time trying to fix up what is likely a damaged screw, I'd look at the cost of a replacement.

KIWA EXCEL 510 CNC MILL 29" BALLSCREW | eBay

If this is similar to my KIWA Excel, there is a Z axis brake on the counter weight chain. If you are having any issues with the tool changer limit switches it won't release the z-axis brake.

Edit - I see your counter weight chains are loose so probably not your issue.

If the ballnut was seized with rust and you got it free I can't imagine holding much of a tolerance with the machine. Even if tolerance isn't an issue backlash is a bitch with getting finished surfaces to blend nicely. I would be doing a complete audit of the machine and make sure it is worth the work before fixing one problem to find another.

Generally I won't touch a machine that's been outside more than a few days regardless of the price, but that's just me.

homanfab said:

If this is similar to my KIWA Excel, there is a Z axis brake on the counter weight chain. If you are having any issues with the tool changer limit switches it won't release the z-axis brake.

Edit - I see your counter weight chains are loose so probably not your issue.

Click to expand...

is yours a 510? where is that brake? just curious. ya I have the head supported and the counter weight bolted to the casting so the chain has no tension

so apparently the ballnut/screw is greased not lubed..that line I thought was ballscrew lube must go somewhere else

so a flushing operation may not be possible here

I've got to admit this is all a bit weird..not sure how or why the ballnut would have "rusted"...is there some other phenomenon that could make it appear seized? what if somehow the head went below its normal travel?

laggeddag said:

is yours a 510? where is that brake? just curious. ya I have the head supported and the counter weight bolted to the casting so the chain has no tension

Click to expand...

It is on the right end(facing the machine from the front)of the shaft the supports the sprockets for the counter balance chains. Looks like a little can with a couple of wires.

My machine is a Excel 4L, not a 510/Colt. Looks similar but doesn't have the full enclosure.

homanfab said:

It is on the right end(facing the machine from the front)of the shaft the supports the sprockets for the counter balance chains. Looks like a little can with a couple of wires.

My machine is a Excel 4L, not a 510/Colt. Looks similar but doesn't have the full enclosure.

Click to expand...

hmm mine must not have that .. I wonder why yours does

have you ever taken the head off? do you have to take the blocks on the head casting off?

If you need any info I'll share whatever I got..I have manuals for pretty much everything except the individual servo/spindle drives

okay I took a look at my ballscrew and unfortunately it does not look like the one on ebay, not even close. Its got 4 ball screw tubes and it looks like this other used one on ebay: KIWA EXCEL 510-COLT CNC MILL 37" NSK BALL SCREW W3207-249D-C5Z 02A-048 BALLSCREW | eBay I think that new one on ebay might be for the X or Y axis..I'm trying to confirm..it looks similar to the used x/y axis ones so I may get it anyway

Note that the used one on ebay apparently has a lube port! ???? My kiwa manual says the ballscrew is greased..it cant be both right? Now I dont know whats going on with the lube method

My new plan is to clean up the ballscrew as much as I can (the exposed sections), then carefully by hand run the section thats inside the nut out of the ballnut and clean that. At that point if everything feels very smooth I may say I'm done. Otherwise I will have to pull the head (still dont know how to do that with box ways) and take the ballnut apart to try and clean it better

today the ballscrew seemed to spin more smoothly than ever...basically to the point where I would probably assume nothing was wrong if I didnt notice the orange fluid that follows it out of the ballnut

so I decided to take the whole ballscrew out without taking the head off. I did some measurements and it seemed that it should be possible pretty easily, and it was!

Getting the nut at the top of the screw off (that holds the thrust bearings was not easy. I had to use two vice grips on the non-functional part of the ballscrew above the threads to prevent it from turning. The ballscrew is so hard I dont think they even left a scratch. Then I used a flat blade and as a driftwith hammer to spin the nut off. It did not want to go and then suddenly it did. It has brass set screw followers that I think had never been removed and were doing their job (with the set screws out of course).

After that I removed the ball screw shields and jacked the head casting up pretty far. In theory it seems like it has enough Z travel to be jacked up as long or slightly longer than the entire ballscrew length, but I was able to get it out with much less travel since there is space in the casting (see pics).

The head casting and counterweight seem almost perfectly balanced. With nothing but friction holding the head in place it did not want to move up or down. I had to use the porta power to move it up, or smack it with a 2x4 to move it down. Nice! Way better then dealing with something that wants to move.

It was not difficult with a few extensions and a 6mm hex adapter to remove the 4 bolts from the ballnut. It came loose immediately. Its heavy so make sure to have some plan for supporting its weight and gently letting it down once its free. You can do it with just your hands if you are very careful and coordinate grabbing its threads above the head while grabbing its bottom end from the bottom and guiding it out. I laid some rubber mats on the bottom and put the nut back on the top with a piece of wood pinched between it and the casting so it wouldnt fall once free. Oh dont forget to disconnect the lube line! I cut it off right after the cap on the distrib so the ferrule and cap stayed together. Should probably cover the cut tube so gunk doesnt get in there.

This was not that bad of a job really and basically seems pretty routine. I recommend a porta power or bottle jack, several pieces of wood, and the usual other tools (6mm hex on extensions is critical to ballnut bolts out). Make sure not to let the brass followers fling out of the thrust bearing nut once it starts spinning. Ask me how I know about that.

Next phase is to figure out what to do with the ballnut. I guess the whole point here is to clean all the crap out of it. Then clean all the surface rust and gunk off the screw. Thing is, I dont really get this. Is the ballnut just oiled, no grease? It has a lube line which now I confirmed actually is the one going up to the same lube distributor as everything else, so it gets vactra 2.

Nice job. Glad it worked out for you.
Get it cleaned, oiled and back together now !

SteveEx30 said:

Nice job. Glad it worked out for you.
Get it cleaned, oiled and back together now !

Click to expand...

unfortunately the balls and screw have some pretty severe damage

It looks like the damage is limited to the area the ballnut was sitting on the Z axis.

Its still not clear to me why this happened. I guess condensation may have formed on the ballscrew and then it had a perfect path into the ballnut?

Anyway the balls and screw in that area have deep pitting (easily felt with fingerails).

The ballnut seems to actually be in good shape. I havent gone over it in extreme detail but I dont feel or see any pitting. The screw above the damaged zone also seems in ok shape.

I got this machine for free and its electronics are in good shape. I think what I am going to do here is this:

1) Buy replacement balls from ball tec.. should set me back about 25$ for grade 25 6.35mm balls (a couple hundred)
2) See if I can fix the z axis with those new balls, at least enough so the machine is operational while I work on the rest of it/clean it up. I think the tool changer had some issue and I need the Z axis running to work on it. At the very least if I use new balls and keep the axis above the very bottom damaged zone I think that would be fine.
3) Inspect the machine ways and other ballscrews. Inspect the spindle.
4) If the ways are thrashed then I am going to give up on refurbing the machine and I will just liquidate all the parts on it. If the ways are good but other ballscrews are bad, I will continue, because I think I can get my hands on ballscrew replacements for a few hundred each. If the spindle is bad I may continue anyway depending on how bad (bearings or taper and severity)

At the very least I will finally get to try replacing balls in a ballscrew. I want to see what happens and $20 or so on a basically scrap ballscrew is a perfect opportunity