CNC Mill- Replacing Y axis Linear Bearings
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  1. #1
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    Default CNC Mill- Replacing Y axis Linear Bearings

    I have a little mill (Brother) that when I move the table to either extreme right or left the table tilts a little in that direction when the weight gets over to the side. Checked using a Starrett 199 level in the center of the table. The y axis on this machine has had a rough life. It was packed with chips when I got it. I have had to replace the Servo motor and thrust bearing. Ball screw seems ok and very little backlash. I was thinking to install the new linear bearings I could do it one side at a time.

    Move the table along the Y axis so I can remove all the screws holding the rail down on say the left side, loosen the screws on the trucks, and jack the table up just barely so the trucks come free of the bottom of the table. Then slide the rail assembly out. Clean everything, slide the new rail assembly in, put screws in loose, lower the table, move back and for along the Y axis to get it all running true and tighten. Then do the other side the same way.

    Anybody done this who can weigh in on my plan?

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    You're on the right track. That's how I've done it. Used machinist's jacks. You may want to loosen the Y motor mount that the thrust bearings are in. no big issue. The cleaning is what takes time.

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    When you were testing with your level did you also try to measure movement (clearance) between the Y rails and blocks?

    I recently had to replace the Y ballnut grease line on my 30 taper Mori. Based on the small space and essentially no room to work, I think it would be tough to do a good job replacing the rails and blocks with the table just jacked up a bit. Hopefully there is more room on your Brother.

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    Have played similar games on equipment in the past, key thing that really helps, Bondhus stubby allen keys! It can be a slow and painful job, equally clean it as much as you can before you remove anything.

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    Vancbiker: I did not take any other measurement than this, well, I did find that my table is bowed up in the middle but that is another story. I think I can do it. As i said when I got the machine the machine is was pretty packed with crap under there so in the course of cleaning stuff out I took the trucks off to put new end seals on them because the seals were trashed. Also had the ball screw out to clean all that out. Only thing I have not done is remove the track hold-down screws. Just as BrotherFrank said I used a machinist jack screw to hold it up. I may buy another so I have two supporting it.

    Adama: Yea, when I took the trucks out the first time I spent a lot of time figuring out how to work in there. I wound up buying several extra 5 and 6mm Bondhus allen wrenches and cutting stubs off. That combined with a 1/4" air rachet and 5,6mm sockets to make drivers it went pretty quick. I didn't figure all this out until I was almost done the first time though.

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    Quote Originally Posted by Pete Deal View Post
    Vancbiker: I did not take any other measurement than this,
    Was just curious about what all you had done to verify a worn linear way system being the cause.

    Once while trying to figure out an orbit burning accuracy issue on a sinker EDM I finally checked the Z axis block to rail clearance and found that just the pressure of the flushing would create ~.001" movement between the lower blocks and rails. Replaced the blocks and rails and problem solved. Turned out the machine had suffered a few tank fires where the Halon system activated to put out the fire. One of the byproducts of Halon when putting out a fire is a corrosive gas and had "etched" the rails.

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    First thing is make sure you can access all screws holding down the rails moving the Y axis to the travel limits, make sure the center one is not always covered. When I did this the biggest cheek clencher was loosening the little screws that push the rails to the side so you may want to start squirting some penetrating juice on them ahead of time, I had to warm things up with a propane torch as a last resort to get a few screws to loosen. For machinist jacks I used two 1/2" nuts and a stud from my clamping kit. This was for a bridge mill, fixed table, and it was plenty. Go slow, clean, clean, clean, and torque it down correctly. Rail alignment is tight against the stops and block alignment may require shims, not such an issue for your Y axis. Anothe BIG issue is only pumping the correct amount of grease into the blocks. If you overdo it you can/will blow the plastic ball returns off. Find out the grease capacity of the blocks and how much grease your gun puts out with each pump.

    The clamp down holes in the rails have burrs from grinding the tops so every time you pass the block over them without the caps installed you will trim off a little bit of the rubber seal lips, this is something I noticed on mine.

    I remember Tony saying it only took a few hours to replace both Y axis rails and blocks on one of their Brothers.

    I am willing to bet your Y axis rails and blocks are only the tip of the iceburg, you may not want to get started down this path as a newer cnc machine is way better/cheaper than trying to rebuild an old one. Your X axis had the same hard life/ brain fart, and is probably in not much better shape.

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    All real good points- thanks all for the comments.

    Vancbiker- I looked at the rails when I cleaned it all out and posted here that one of the odd things was that the rails did not have plastic caps in the holes for the hold down screw so the trucks were all full of crap. The prev. owner was a die caster so the crap was pretty soft. I took the trucks apart, had all the balls out, big mess. But everything looked smooth including the rails. The X axis may be not a whole lot better but since it does not have the over-the-side weight shift it seems to me it won't hurt me too bad. The finishes I am getting don't seem bad. So the table lifting I think has to be from the Y axis wear.

    DavidScott- You may be right that I am dumping money down a hole but I hope not. I am still a long way from the cost of a new machine though so my intent is to fix some stuff up and hope it will do me for a few years.

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    ^ Rails of the correct class and pre-load are cheap, kinda hard to see how you could not spend more on moving the machine out and the new one in on the cost of replacing all the rails on the machine (the rails bought from a decent bearing supplier over here would be sub £1K for the x and y, from a chinese source even genuine hiwin you could do all three axis for that 1k). If you find tony's old thread you will see i commented on it re the life span of the rails, for the distance he reckoned his machine travelled they sure did die early! Look into the extra sealing options on the hiwin trucks, makes a big big diffrence, if you can get the trucks with the seals that wipe the top of the rail effectifly leave the holled area unwiped but keep the tracked area sealed up - dont need the plugs, because IMHO the plugs are not the best. Far better option is the long shim approach some of the other rail makers use, yeah there fiddly, but they sure wipe well and keep the crap out of the trucks.

    The greaseing comments valid, on smaller trucks, pays to just grease little and often. That said if you have contamination issues, thats were oil as both lube and in effect flush is way better.

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    Pete. Throw the new rails (correct ones from Yamazen/Brother) in and get on with machining. Those new rails could outlast the rest of the machine. Your original rails had several strikes against them. The machine came from a die caster (no offense to shops doing things right). Generally 24 hour service with little to no maintenance. They probably used synthetic coolant which washed out any lubrication that was there and allowed rust (poor concentration). If it was die cast aluminum, it has high silicon so it is actually very hard in spots acting like lapping compound in there. They probably never greased it. I am making a lot of assumptions but most likely accurate from my experience. Keep it clean and greased and they will last you 30 years as long as you aren't machining stuff like graphite etc. I have only seen a few brother machines that needed rail replacements out of close to a thousand, some 30 plus years old. Ball screw work more common, usually from the same reasons.
    Last edited by BROTHERFRANK; 02-28-2018 at 10:36 AM.

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    Quote Originally Posted by adama View Post
    ^ Rails of the correct class and pre-load are cheap, kinda hard to see how you could not spend more on moving the machine out and the new one in on the cost of replacing all the rails on the machine (the rails bought from a decent bearing supplier over here would be sub £1K for the x and y, from a chinese source even genuine hiwin you could do all three axis for that 1k). If you find tony's old thread you will see i commented on it re the life span of the rails, for the distance he reckoned his machine travelled they sure did die early! Look into the extra sealing options on the hiwin trucks, makes a big big diffrence, if you can get the trucks with the seals that wipe the top of the rail effectifly leave the holled area unwiped but keep the tracked area sealed up - dont need the plugs, because IMHO the plugs are not the best. Far better option is the long shim approach some of the other rail makers use, yeah there fiddly, but they sure wipe well and keep the crap out of the trucks.

    The greaseing comments valid, on smaller trucks, pays to just grease little and often. That said if you have contamination issues, thats were oil as both lube and in effect flush is way better.
    They may cost a little more over here, and you will spend several days figuring out exactly what you need, and there is a lot to figure out. WATCH OUT FOR HIWIN!!!!!! The distance from the bottom of the block to the bottom of the rail is 1mm less than any other manufacturer I looked at. On my machine I had .5mm clearance between my old blocks and the machines casting. I had to grind 1mm off the castings to get the Hiwin rails and blocks to fit. Hiwin was by far the best price and no complaints about the quality of their product, just their packaging, which was a total joke.

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    ^ Can't belive you pay more from them, unless its from a local bearing place robbing you, in which case china or tiwan directs your best option. For a 25 sized std length block either flanged style or the block style there typicaly around £50 each here. its really not that hard to match what you want, there only a hand full of common blocks and the rails are easily measured and compared to your rails. Can't help you on the 1mm less thing, but i know theres a lot of varieties and no standards between the diffrent OEM's with linear rails unlike with say std circular bearings.

    Yeah hiwin packaging could do with shall we say a little padding!

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    I jumped in with both feet- ordered the rails, new spindle, upgraded memory board from Yamazen. Hopefully to get another 5+ years out of this machine. I will continue to drool over the new ones in the mean time.

    Adama: The rails on it are NSK. I spent a lot of time looking at the book, looking at the rails, preload options, etc. If I had a good local bearing supplier I might be more inclined to try this. Our local bearing companies have all been bought by a big company, Motion industries, and the old guys who knew about anything have retired.

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    They are not that expensive from Yamazen. They aren't that bad to change, few hours We've done 1 set on an S2C machine, it had about 10 million cycles on it at the time. The beauty of these Brother machines is they are really are designed with the KISS principle. They are very easy to repair.

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    Quote Originally Posted by Tonytn36 View Post
    The beauty of these Brother machines is they are really are designed with the KISS principle. They are very easy to repair.
    That's why my next Fadal is going to be a linear rail machine, rather than the box way machine I have now, which is going to need Turcite soon.

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    Quote Originally Posted by triumph406 View Post
    That's why my next Fadal is going to be a linear rail machine, rather than the box way machine I have now, which is going to need Turcite soon.
    Why not a Brother? We just installed one at a 'fadal shop' in Corona and they knocked 60% off the cycle time of the first job moved over to the Brother with the identical feeds and speeds.

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    Ok new spindle in and balanced, and new slides are in. Very straight forward process. Spindle change out is like a 2 hour process even not having done it before. I think the second one would be an hour+. Slides are more involved mostly because taking all the way covers off. Even that is pretty easy. About 6-8 hours for the slides. One mistake I made was after reinstalling the way covers last time I looked up into the back into the Y axis with coolant running and coolant was dripping all over the place inside. I took the covers off and put RTV between the covers and the table. That stuff stuck like crazy so getting them unstuck this time was difficult. I think I will use some foam tape this time. The trick to changing these slides out is having a 2-3 5mm allen wrenches with the ball end. I cut the ball end off one of these and put it in a 5mm socket and used an air ratchet to run the inner ones in and out.

    The other thing is that for whatever reason with this vintage machine Brother did not put caps on the linear bearing screw holes. I added them when I got the machine during clean up. The new rails did not include the caps so I need to order some and put them on before I button things up. I could not find a way to get ones that I had put on the old rails out without destroying the old ones.

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    The way to remove the old caps is with compressed air. Blow on either the tiny center hole if you have one or at the edges. I hope you used a torque wrench to tighten the rail and block mounting bolts! I use a silicon gel lubricant to seal my way covers to the machine. It is for pool filter housing o-rings, similar to o-ring grease but cheaper, and I already had it laying around.

    Did you get the rails and blocks from Brother? I can not understand how they could possibly not provide the caps, they are F%$KING critical to keeping the chips out of the blocks. THK does'nt provide them either and charges 70 cents each for them, Hiwin included them at no extra charge.

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    I got the whole thing from Yamazen. I agree that the caps ought to be there but the thing sure did last without them. These caps did not have a center hole that I could see. They are $1 ea from Motion so what the heck.

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    Just out of curiosity, did the new rails and blocks fix your problem?


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