Mori Hori bad linear rails
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  1. #1
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    Default Mori Hori bad linear rails

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    A little loose,eh?
    So what's the best course of action?
    Junk the machine?
    Swap in new rails and trucks?
    Repair ( reball?) Trucks?

    So much great info here!
    TIA

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    If you are sure there's nothing else that could drive the carriage to tilt, then I'd do a very careful inspection of the linear track. If it seems to be in good shape (measures uniform in parallelism along the length, straight with an external reference), then I'd look at reballing or new trucks. Reballing would be easiest, but would still require real care to not degrade the performance of the lathe.

    If it's not too hard to do, I'd try decoupling the ballscrew and manually driving the carriage back and forth, as well as trying to "rock" it to test for looseness at the trucks. Also, you may want to tune the Z servo, not sure but it sounded like there was buzzing as if it's hunting.

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    Thanks Milland.
    Buzzing might have been some lite whittling on some Ti..or the Y axis whinning (another story lol)
    600mm Hori MILL, not lathe. Sorry, my bad.
    Not sure how anyone would take the trucks off the rail while they're still bolted to base, as toolchanger or control cabinet are at the ends.

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    Hah - made the assumption it was a lathe, my bad. How old is the machine, been run hard? Any issues with oiling to the linear rails?

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    not clear how much movement you have on those rails but you may find the balls to be of a standard size. i would replace the balls and you don't need to remove the rails from the block to do that but it may be a pain in the ass to remove the end seal and feed the balls in one by one. for the balls retained in the end seals you can use grease to hold them in place. You don't have to replace all of the balls either. if they are .125" balls (probably worn down to .124 given your video) replacing 2 of the tracks with say .126" balls may be mechanically equivalent with replacing all of them with .1255"

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    I'm really glad it doesn't seem to be the spindle!
    The .0005 indicator is moving about .003 while running .500 endmill. Shows up very pronounced in floor finish whenever there's a load on X.
    Taking anything close to a decent cut the wobbly sound takes over (right before the cutter blows), so I wouldn't be surprised if a couple trucks have no balls.

    How many days would a professional mehanic charge to reball?
    Thanks guys

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    Quote Originally Posted by mkd View Post
    I'm really glad it doesn't seem to be the spindle!
    The .0005 indicator is moving about .003 while running .500 endmill. Shows up very pronounced in floor finish whenever there's a load on X.
    Taking anything close to a decent cut the wobbly sound takes over (right before the cutter blows), so I wouldn't be surprised if a couple trucks have no balls.

    How many days would a professional mehanic charge to reball?
    Thanks guys
    How many trucks on X? If four (two left, two right) then it's pretty unlikely there's no balls in any of them, table would be floppy up and down. If six or more, then maybe an end cap broke or some other leak occurred. If you want, take your indicator and with the table bare, place it over each truck, whack the table with a soft dead blow hammer, and note if the indicator really jumps over one or two spots.

    On reballing, I dunno. It depends hugely on access, cleaning time, and whether the table must be pulled or not. And you do want to double-check the lube system too, any repair without doing this is risky.

    As to post #5 and just reballing two bearing paths, I respectfully disagree, if there's significant wear in the truck bearings they're likely OOR in the balls too, not uniformly smaller. So you really do want to get new balls in all tracks after cleaning thoroughly.

    Speaking of, some of the cost you'll get is the possibility of buying a number of balls in step ranges, so the repair person can try various combinations to come to the right fit for each truck. Real pain, but I don't know a better way to get preload right, assuming no drastic or uneven wear (which may require full rail and truck replacement).

    Watch for table height variations if it's removed and reinstalled, and check for shims at each truck pad. If you are careful and don't mind trimming the table surface, you can recut the table top to bring it back to flatness relative to the spindle. Be sure the machine is squared first, with each foot pad having the right load on it. Might be a good time to anchor the mill to the floor if it's not already.

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    If you reball the trucks you would likely have to alternate the size of balls, 1 ball the correct size, next ball slightly smaller maybe .0005-.001 smaller if I had to guess. Reablling isn't going to help much if the rails are trashed

    Look at the cost of new rails and trucks, may not be that expensive if Mori used COTS rails and trucks. Hiwin rails would be ok, genuine Hiwins that is, not the ebay knock offs

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    mkd - are there many rebuilders in your neck of the woods?
    It would be a huge ballache saving if someone would visit and do it on site. May cost a couple of nights in a hotel + flights but if they could get the machine 90% like new, would be a cost effective solution?
    I don't know this company, but San Diego isn't too far away.... LINEAR GUIDE REPAIR - Ross CNC - Ball Screw and Spindle Repair

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    Thanks for the link BARB :wink:

    Talked to one outfit yesterday that claimed to have never heard of reballing trucks. Another outfit hasn't returned my email about it even though they were the ones who gave the spindle a clean bill of health.

    Also thanks for the hiwin mention.

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    I have reballed trucks. It's a pretty time consuming job. The ball returns and seals are normally shot so you need to track those parts down. Then you try to figure out what balls you need and order them.

    The machine I did had spacer balls that were .001" under the load balls. That is what makes it take so fucking long.

    You also have to mill up some fake pieces of rail so you can load and assemble the trucks then slide them on the real rail.

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    Thanks for your experience, Garwood.
    I was afraid of that, as the ends of the rails are blocked by either the tool changer or control cabinet. Having no experience in this area I was holding out hope that new balls could be stuffed in while mostly in place.
    Sounds like jacking the A frame off the rails and swapping new ones is the best solution.

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    Quote Originally Posted by mkd View Post
    Sounds like jacking the A frame off the rails and swapping new ones is the best solution.
    New trucks and rails? If so, you may want to special order them for higher preload and accuracy than what you get off the shelf.


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