THK Linear Bearing Clean-Up

All,
I just got some THK HSR20 linear bearings from Ebay. They are a pair of 48" rails and 6 trucks. However, they appear really dirty and sticky. If the rails are held vertical the trucks will not slide down. It does not appear to get any better if they are loaded (ie the trucks are not preloaded). They have a really sticky black grease on all over them that appears to be gumming them up. My question is how do I go about cleaning them up??? I think I can carefully take the trucks off and clean the rails and the trucks without losing any balls as they are not caged. Is this a good idea???
Also, the Ebay listing said good condition and after carefully sliding one of the trucks off it appears that some of the balls are missing. I don't think it will make a difference, but should I say something to the seller anyway. The bearings still seem extremely rigid on the rail, just a little sticky.
Thanks,
w102acd

Hi w102acd,
Check this thread, where I gave some info of how I cleaned my HSR 35's. http://www.factorydaily.com/forums/showthread.php?t=67361 (linear rail hsr45)
You can also send me a PM, and I can give more info about this.
Check if the end seals are sticky like chewing gum (caused by agressive coolant and/or way oil). If they are not OK and do not scrape the rails properly, they will let dirt enter the ball races which are bad news.
If you will buy new seals, I recommend that you buy the "SS" seal sets which include End seals, Inner Seal, and Side seals.

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Viking,
Thanks for the reply. That is some great stuff and the picture of the truck you have is exactly what I want these to look like. What type of cleaner/degreaser did you use??? I assume mineral spirits are out of the question and a detergent cleaner also scares me.
Do you see any problem with a few balls missing from some of the trucks?
Thanks,
w102acd

Hi,
I used white spirit and a small flat paint brush. The end walls are made of some hard plastic. Clean them and all seals you are going to re-use and wipe off with paper towel asap. Note!, don't loose any of the 4 small plastic "ball roundabout" inserts that are placed in each end wall.
Pour white spirit in the empty truck body to clean all ball races and return bores. Finish by blowing with compressed air.
When reassembling, mount one of the end walls, the bottom ball holder and the side seals. Let the truck rest on the end wall, push some ball bearing grease in the ball return bores and start loading the cleaned balls in one race at a time. Mine had 31 balls in each race. Note!, the 2 last balls in each race are to be placed in their corresponding places in the second end wall with a good blob of ball bearing grease.
NB, Do not forget to push the inner seal into the first end wall's pockets before you reassemble the second end wall.
Install the end seals and brush all visible balls and all seal's lips with ball bearing grease.
Do not forget to unscrew the oil metering bodies from the elbows and check if they are clean and let oil through.
As for lubrication, an Auto-Lube system is highly recommended.
Reinstall the completed trucks (push them gently and firmly) on their original, cleaned and lightly oiled rails, in their original directions.
And please read the other thread I mentioned earlier about not working with several trucks at a time, not mixing trucks from other rails, not mixing balls between trucks, not mixing balls between races etc...

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Viking,
Thanks for another reply. I did look at your other post. I was a little confussed about the parts you were talking about. So I just disassembled one and quickly found the parts you were talking about. I was not able to keep the balls from each race seperate, but did not mix them with another truck. Anyway, I am not sure what white spirits are so I just used laquer thinner that I had around. I used the same method that you described in the previous post and all went really well. Each race appears to have 50 balls in it (supposed to anyway). Unfortunately, when I disassembled the truck only 195 balls came out of it. I guess that's Ebay for you. So I split the balls as evenly as possible (49/49/49/48) and reassembled everything dry. I didn't have any grease laying around and read other places of people using them dry without a problem. Note: I am not saying I will be using them dry. I clean the rail with some thinner and put the truck back on. At first I was not impressed and found that the seals were sticking. I took them off and WOW did that make a difference!!!
I realize that the seals are very important so I put them back on and the trucks were sticky. I grabbed a can of WD-40 and sprayed some on the rail. The truck now slides very smooth and will slide with the rail elevated about 45 degrees or so. Before they wouldn't even budge with the rail held vertical.
I have not heard of anyway using WD-40 as a lubricant. Is this a bad idea??? The plan for these bearings is to use them for the x axis of a medium sized cnc router. The router will be used very lightly compared to production machines. Probably somewhere in the 2-10 hours a week seems about right.
Another question: On each rail, is it better to have two trucks with all of the balls or three trucks missing five balls each??? Can I sacrifice one truck per rail to fill the other two trucks with balls???
Thanks again for the info and sorry for the long post,
w102acd

w102acd ,
The "white spirit" I mentioned is also known as Kerosene. Do not use laquer thinner as it contains toulene which attacks rubber.
This is how I disassembled my trucks so I could remove the balls from one race at a time:
Do not remove any of the end walls yet!
PLace the truck with the inside upwards. Tilt it slightly towards you and remove only the

that is towards you.
Hold the truck over a container and push the balls in that upper race sideways so they fall out of their race in the opposite end. Any balls still in the return bore can be removed by
blowing compressed air into one of the end wall's ball entrances.
When all balls are removed from this race, do the same with the other side's upper race.
Do still not remove any of the end walls until all balls are removed from at least 3 races!!
In order to be able to remove the balls in only one of the lower races, I made a simple sheetmetal retainer, so I could block of one of the races. See piccture THK, HSR 35-4.jpg. Install it where one of the side seals used to be and then remove the bottom ball holder. See THK, HSR 35-5.jpg when istalled. Remove the balls from the open ball race. Remove the temporary retainer. Now you can disassamble the end walls and the remaining balls from the last race.
Of course, you should now have the balls from the 4 races clearly separated in marked containers so you know where they go back after cleaning. See picture THK, HSR 35-6.jpg
And you SHOULD, like I said earlier, pre-grease them during re-assembly with a good ball bearing grease to protect them until the machine's own lubrication system or your greasing shedule are effective.
Lubrication:
WD40 is only good for lubrication of door locks, and temporary moisture protection. It has no place inside precision heavy duty components like linear guides.
The linear ways are certainly VIP's on any CNC and should NOT be used without lubrication. Either use a central auto-lube system or periodically grease the trucks through nipples placed on each truck. You may find that periodically removing dust covers in order to get access to grease each truck will be a real PITA.
For Auto-Lube systems THK recommends Mobil Vactra2 or Shell Tonna 68 oils. The Auto-Lube settings may be different depending on which type of metering valves you use, but my system is set like this: Pressure valve=3,5 bars, lubrication frequency=once every 10 min. (this is for production), lubrication duration=30 sec. each time. As for grease, you have to visit THK' website for information on grease types and greasing frequencies.
Seals:
If they are dodgy, CHANGE THEM!! You will regret not having changed them when you find that chips and dust have ruined your fine THK trucks, or in best case you have to do the clean-up work all over again.
About removing trucks from a rail and only use 2 of 3:
I have a heavy 950 x 420 mm cast iron table that runs on 4
THK HSR 35 trucks. My industrial VMC accepts work pieces up to 500 kgs. Each trucks centre is 240mm inwards from each end of the table. The X-axis has 300 mm between the rails. Are your trucks preloaded? Judging from the higher ball count in each race, your HSR 20's may have smaller balls than the 1/4 inch balls, in my HSR 35's, so I think they are specified for lower loads.
It is depending of your load situation of course, but I think that I would have kept all 3 on each rail just where they are.
If you want to remove one truck from each rail and only use 2, you should carefully mark them (rail and direction). Check carefully the ball diameter from the "ball donor"! It should be ideally within 1/2 micron of the receiveing truck's ball diameters. Use a "micron" micrometer to compare the balls with. See picture THK, HSR 35-7.jpg

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Viking,
Thanks for another reply. This seems like a bit of overkill for the rails and trucks I am starting with. Some balls seem to be missing from every truck and the grease zerks were not on the same side of all of the trucks. So this tells me that the trucks have been removed and the direction has not been maintained.
I have disassembled all three of the trucks on the first rail and have them all sliding very well. I did not concern myself with keeping the balls in each race seperate. The seals seem to be a little gummy from the grease and probably need replaced. I looked on the THK website and store, but didn't find anything useful. Where can they be ordered from???
My trucks slide the same with and without load, so I think they are not preloaded. I think I am going to keep three trucks on each rail as you suggest. Just curious though, is it possible to put these trucks on another HSR20 rail??? Meaning if I find some rail can I put the two extra trucks on it.
This machine will be more of a hobby machine. So if I can't lift it, it won't go on the machine.
Thanks,
w102acd

All,
Does anyone know if a THK KR33 would work well for the Z axis???
Thanks,
w102acd

W102acd,
I agree, you will be OK with periodic greasing for the use you mention.
THK?s North American Headquarters are in Shaumburg, IL. Phone: 847-310-1111.
They have another 7 offices in the US of which 2 are in California. They also have one office in Canada.
The oil metering bodies on my trucks are placed on the end wall that is faced towards the other truck on the same rail. The other end wall has a screw-in plug and you can swap positions as needed.
The precision ground side surface of each truck is faced towards the other rail (towards the centreline of the table).
Preloaded trucks are a little tighter between the upper and lower races and thus they apply a bit of ?pinch? on the rail?s wings. When you put a heavy weight on top of the table, it will relax pressure from the lower races and the truck gets more ?loose?. This is counteracted by preloaded trucks. Non-preloaded trucks have zero-play or are even loose to start with and so they become even more loose under heavy load. Although more expensive, for heavy duty machining preloaded trucks are the way to go. I am glad I have them and will take very good care of them.
In short, the above suggests that ideally they shouldn?t really fall off the rails too easy.
About moving 2 trucks to other rails:
I have seen ball diameter differences up to 2-3 microns in trucks from different rails, so either you could end up with too much ?preload? or too much slack. I would rather try to get complete rail/truck sets.
Look up the part No. at the top end of your rails and post it here. Then I can check in my THK catalog what type of rails/trucks you have got.

All,
Does anyone know if a THK KR33 would work well for the Z axis???
Thanks,
w102acd

Not a bad idea for light duty CNC's!!
The KR series are LM Guide Actuators ( one "reversed" LM guide with an internal ball nut that is driven by a included ball screw. However, I think that the model KR-B would be much more rigid as it has two nut block units.
10 mm lead is quite fast too. Call them and get their A+B catalog set. It can answer all your questions about LM guides and Ball Screws.

Viking,
Based on the size, the trucks are HSR20LR.
I will have to call my local Motion Industries tomorrow morning for the end seals.
My KR33 only has one truck on it. So I guess it is a KR33-A. I may start with it and build my own z axis later. It was too hard to resist an axis already built.
I have one more truck to clean and replace the end seals.
I was looking at bearings for the y-axis. Any opinion on NSK or IKO brand bearings???
Thanks again for the replies,
w102acd

Viking,
Based on the size, the trucks are HSR20LR.
w102acd

They have the same cross sectional dimensions as the compact HSRxxR series, but are longer (in your case 16 mm longer) and thus the load rating is greater. Quite a bit actually! Good for you.Take good care of them.
The greater length also explains the higher ball count in your trucks.

Just got a message about the end seals. They are $7 (USD) each. If I replace them all I will have $84 into them. This is about half of what I paid for them. I always thought I would have the trucks as close together as possible; therefore, the open rail between the trucks would be nearly non-existant. Would it be alright if I just replace the ones on the outside??? This will reduced the number of new seals to 4.
Thanks,
Andy

Andy,
Is that for 1 end seal only? What about the side seals and the inner seal? Are you not replacing those. The inner seal seems to be an "option" as it was not present originally in my trucks. I paid $ 32 per complete set x 10 sets. If I had not bought 10 sets, the price would have been $ 50-55 per set.
Anyway, don't be cheap now. You only want to go through this once, and then forget about it for another 8-10 years, right?
If you got the rails and trucks cheap, that is not an excuse. On the contrary - see it as your luck, now you can afford the seals as well!!
The only reasons to place the trucks close to eachother should be physical limitations. If you can, you should separate them as much as possible to get maximum guide length. This gives you a more stable and rigid machine.
Post some pictures of your machine so we can see the design and proportions. If not ready yet, explain the design and major dimensions.
Cheers,
Peter

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