584,829 active members*
5,059 visitors online*
Register for free
Login
Results 1 to 4 of 4
  1. #1
    Join Date
    Jun 2013
    Posts
    52

    Ballnut balls fled

    It just keeps coming out wrong for me...

    If you're bored here's some background:
    So yesterday night I started disassembling the crosstable of my new BF20L (G0704 like) in order to replace the leadscrews with ballscrews.
    I had to quit at some point because I couldn't remove the side plates from the table, because I didn't know I had to remove the little pin between the leadscrew and wheel.
    So when I found out today I continued to disassemble it all with no major problems.
    So I'm going to happily put the Y axis ballscrew in and I realize the ballnut has a grease nipple and the way it came mounted on the ballscrew (although I had to remove it first) won't let the ballscrew shaft fit onto the holding hole opposite the wheel end, because the grease nipple touches against the wall.
    Attachment 282968
    The brass nipple was on the right side of the ballnut and the shaft wouldn't fit in that hole where it's fitted upper side of the picture.
    There was just not enough room, so I thought that was strange, but I would just remove the ballnut and turn it around. All right, I knew that could mean problems, because ever since I started looking at CNCs I've heard when ballnut balls come off you're screwed. But I noticed they packaged a small white plastic tube along with the Y ballscrew that could fit one end and I figured out it would help prevent the balls from escaping when doing this kind of operations.
    Attachment 282950
    And it worked out pretty good. Yeah... uhm I know that picture and my previous comment don't stick well together and looks hilarious with all the little balls laying around there LOL but bear with me, they came out at a later stage.

    Now there was a different problem, although the ballscrew shaft would fit nicely, now I was unable to sink the ballnut low enough to move the Y axis part that slides along the base, over the ballnut, because of that protruding step that runs along the left side under the nipple, as you can see in the first picture above.
    After much fiddling, I could lower it just enough to do it. However, I had to detach the ballscrew and hold the nut carefully grabbing both ends of the white tube. Now I had another problem, I couldn't push the ballnut upwards to fit into the Y part housing. The way I had lowered it, I could only bring it back up if I turned it somehow. So I kept trying for a good while until it just happened what was meant to happen. It fell off my hands and I had the creeps.

    I couldn't hear any bouncing noise so I still had hope that the balls hadn't come off. The white tube was off but I couldn't see any balls under the mill base. I picked up the ballnut and took a look inside, and I could see most balls stuck spiraling around the inner side, except two of them that were near an edge. I didn't want to give it much thought so I just tried to put the white tube in carefully. I was just hoping they would all fit into place and that's all. Was I wrong... The white tube pushed all the balls you see in the second picture out. I thought I'd just try to put the ballscrew carefully, and somehow I'd be able to insert ball by ball as I turned it... Again, very wrong...
    Attachment 282958
    As per the picture, the ballnut would now only move towards the right, and guess what, you can't take it out the ballscrew through that end. I tried to move towards the left but I decided to quit as I was putting too much force, clamping the ballscrew and all, and I don't want it more broken.

    And here comes the funny stuff:
    Attachment 282970
    The piece on the right came bolted onto the ballnut, on the left. HAD I THOUGHT and removed that piece from the ballnut FIRST, I could have easily fitted it into the Y part housing and I wouldn't have run into this (serious, I think) problem.
    Attachment 282964
    So the ballnut is missing some balls and I can't slide it out the ballscrew. I removed all the little hex screws to try and open the side plastic covers. I tried to pry with a small flat screwdriver but there's no room. Please, tell me I can fix this myself, because in no way am I going to spend another 300 euros in a new ballscrew. Mind my economy and country.

    Thanks

    Last but not least, the messy state of the disassembled crosstable
    Attachment 282966
    Yes I need to make (read not buy) me a support stand when I have the time.

  2. #2
    Join Date
    Jun 2013
    Posts
    52

    Re: Ballnut balls fled

    Fixed. (Kind of)

    Today I watched some videos on assembling ballnuts and I got a rough idea of what to do.
    I first tried to pry on a wiper and it wouldn't budge. I saw in a video it should unscrew over the ballscrew. Unfortunately since I didn't see any marks to unscrew it I thought it was a different type and that I just had to pry on it. I was able to take it out like this but I almost broke it. Fortunately the hole I made was not through.
    Attachment 283422
    It couldn't be so hard, so for the other one I tried to unscrew it and it came out easily. The thing is they're built to be very close to the ballnut and ballscrew threads, so dirt doesn't go in, or so I think. So even though the wiper doesn't screw onto the nut, it does onto the ballscrew for this purpose.

    Once I got the wipers out of the way I saw a ball standing out of the thread and I thought "Aha! That's the troublemaker". I took it out and tried to move the ballnut towards the free end. No go.
    I could see some balls deep inside and tried to reach them with the screwdriver and move them to see if I could make the ballnut move. Nothing...
    I moved the ballscrew on my hands looking and thinking. I then realized the protrusion on the capped side was not part of the ballscrew and was screwed on it.
    Attachment 283424

    So I thought that I could unscrew it out of the way and slide the ballnut towards that end to get it out and try to fix it. So I attached a grip on it and then I thought the ballnut itself would be a good counter support. I thought that I'd try that, because if I couldn't unscrew the cap and the ballnut would finally slide to the opposite end, that'd mean the jam wasn't too serious, and if the cap unscrewed, well then I'd finally bring out the ballnut through that end.
    Attachment 283426
    So I proceeded exerting some force until I heard a crack and I was "ok, I broke it, let's hope it can be fixed", and I was finally able to bring it out. The cap didn't move, btw.
    I got some shards of balls, probably from two or more
    Attachment 283428
    I tried to screw the ballnut back and it slid smoothly. When holding the ballscrew vertically, gravity alone would make the ballnut spin downwards. I thought I was lucky nothing big seemed broken.
    I then proceed to put back all the balls in the ballnut, but I was just able to put one or two... I had to look and think again.
    I noticed 4 of those recirculating track thingies... So I thought maybe the balls belong to those in the middle.
    I hesitated between the "it's good enough as it is now" and the "what the heck, let's try to fix it completely, it can't get any worse".
    And so I removed the tube that holds the balls in place and tapped the ballnut on the table until most balls fell. I then removed any other stuck visible balls from the ballnut and counted them all. 69 (heh), plus I'd say 2 from the shards, and 1 that just got lost. 72, among 4 recirculating thingies: 18 per thingy.
    Attachment 283402
    I had to make a lot of guesswork until I got the right way to fit the balls properly. I wish I'd have had help.
    This is how I proceeded:
    For each of the recirculating tracks, I'd set them downwards, I'd insert the ball holding tube from the back up to the recirculating track piece. I'd then drop a ball into such piece, using a screwdriver and with the help of grease. When the recirculating tracks are full, balls start to flow aside through the thread. I just moved the balls out of the way from the recirculating track, carefully with the screwdriver and following the thread. I'd then continue to drop more balls near or in the recirculating piece.
    I first completed both inner ones, as they were more difficult. I'd do one through the closer end, then move the tube all the way through and do the next one through the other end, closer to that one. I then did the outer ones in the same fashion.
    When I finished putting the 18 balls into the first one, I noticed there was plenty of room for more balls, so I put an extra ball. I thought of making it 20, but it would be way too tight, so I left it at 19.
    Therefore I ended up with 3 tracks of 19 balls each, and 1 of 12. An outer one. I thought it would be better if I balanced the balls on both outer ones, but since I was planing to buy some new balls and replenish it ASAP, it didn't make much sense as it'd mean extra work.
    It took quite a while and I thought I wouldn't be able to achieve it as I'm not specially skillful, but in the end it turned out not to be that hard. I set the last track balls in under 5min.
    Of course I tried it on the ballscrew and it worked just as well as before. I tried pulling back and forth and I couldn't notice any backlash. I suppose there must be some, but as a newbie I just didn't notice it.
    I then put the wipers back. This proved to be harder than expected. You need to position them correctly and not make the little screws too tight, or the ballnut won't move.
    Finally.
    Attachment 283416
    I was eager to try it on the mill so I installed it and I was delighted with the precision. I know I'll have to remove it again to put the balls I'll buy, but I couldn't help it.
    Attachment 283418

    I did notice some little notches in the ballnut threads and in the ballscrew. Well, just one notch at each. But it doesn't seem to affect the functioning much.

    I'll now have to find out what balls this ballnut uses, as I don't have a micrometer. If anyone is willing to help and save me from hours of internet browsing, please do. It's a Hiwin ballnut for Optimum. I think it's a 1605 and it's for an Optimum BF20L.

    Thanks

  3. #3
    Join Date
    Jun 2012
    Posts
    182

    Re: Ballnut balls fled

    The inexpensive Chinese micrometers are as accurate as the more expensive ones. Just order one from Aliexpress. It's really the only way you can get the correct size. Some ballnut manufacturers (and users) use different size balls in the nuts in order to remove backlash.

  4. #4
    Join Date
    Jun 2013
    Posts
    52

    Re: Ballnut balls fled

    Hey elfrench, thanks. Yes, I already found and bought a cheap micrometer. They are around 2.38mm in diameter. I bought a 100 of them as they were extremely cheap, for future replacements. I also bought some lithium grease and it's all good now As for the different sizes I think I saw a video of a guy replacing with bigger ones to reduce backlash, that's interesting stuff, but I just hope I won't need to go there.

Similar Threads

  1. Ballnut - Odd number of balls? WTF?
    By Wallybanger in forum Linear and Rotary Motion
    Replies: 7
    Last Post: 10-12-2014, 08:20 PM
  2. I have all these little balls.
    By Georgie in forum Linear and Rotary Motion
    Replies: 1
    Last Post: 09-01-2009, 09:50 PM
  3. Oversized balls in ballnut
    By Bluedog in forum Benchtop Machines
    Replies: 2
    Last Post: 05-15-2009, 04:04 PM
  4. What size is CNC fusion thomson ballnut balls?
    By alexccmeister in forum Linear and Rotary Motion
    Replies: 7
    Last Post: 08-30-2008, 11:20 AM
  5. Preloaded ballnut vs stock ballnut.
    By spaceballs_3000 in forum Benchtop Machines
    Replies: 12
    Last Post: 04-24-2008, 07:35 AM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •