ballnut - balls back in via the side cover and using less balls than original

[dsc]

I got myself a ballnut and of course had to cock up ending with the balls all over the floor (ha!). I've tried re-fitting the ballnut with everything that came out of it (minus 2 balls I think which got lost somewhere), but I'm struggling getting everything back inside the ballnut without a ball or two somehow getting in the unused lines and getting stuck in effect. I'm fitting everything through the side cover, like this:

http://i1120.photobucket.com/albums/l496/dsc_MT/random/ballnut.png

[ignore the balls on that photo, it shows balls where they shouldn't be]

I've marked where the balls are pushed in, I do one ball at a time, stick it in with non-magnetic tweezers and move on to the next channel, so three balls, slight rotation of the ballnut to make a bit more space for new balls, fit another 3 and so on until I can see balls coming out on the other side. There's three circuits in the ballnut and I try to fill them equally.

I can fit all the balls apart from 3 and everything rotates smoothly. If I try and fit the last three, the balls barely fit in the channels (ie. the balls fill the channel around the ballnut, so start coming out on the other side), so when I put the side cover on, something must be ending up pushed into the wrong channel and then rubs / rattles inside as I move the ballnut.

The main question is, am I ok with 5 or so balls missing, or is it going to cause issues? another idea to get around this is put everything apart from the 3, then use some grease on the back of the cover where the return grooves are and stick the 3 there, before putting the cover on.

Regards,
dsc.

[Jonathan]

The main question is, am I ok with 5 or so balls missing, or is it going to cause issues? another idea to get around this is put everything apart from the 3, then use some grease on the back of the cover where the return grooves are and stick the 3 there, before putting the cover on.


Having balls missing will effectively reduce the load rating of the nut, which in turn will shorten its life. So if this ballscrew is for your average diy CNC router that's probably not an issue, as if you calculate the lifetime with the relatively small forces on a router, they'll last for many years. Many years minus a bit is still a long time.

However, you should be able to get them all in. The grease idea sounds good. You could put as many as you can in, unscrew the nut on to a tube, stick a large magnet to the side of it (so the balls don't fall out), then poke the rest of them in. That's the way you'd do it if there was no access through the return channel, as it's generally more difficult than the former. The following pictures show this process:

1061310614106151061610617

[Ralph]

Put the return track cover back on.
Put a light film of grease inside the nut.
Stick all the balls into the nut in the correct places.
Make a roll of shim just under the core diameter of the nut and balls and then slide the nut onto it making sure the balls stay in place.
Offer this up to the screw and wind the nut back onto the screw shaft making sure the nut is the right way round.
If necessary, wash the grease out with paraffin and apply the correct lube.
Sit back, drink beer.

[dsc]

Thanks for the tips gents. I've tried the magnet method, but the magnet wasn't powerful enough and so I ended with half the balls out again. This means I will go down the grease route and stick all the balls in manually.

Regards,
dsc.

[dsc]

Ok got the ballnut greased, divided all the balls into three groups with even amount in each and put them in the three circuits, making sure everything is nice and tidy. Carefully used a piece of ali tubing which came with the ballnut, to secure the balls in place ie. slid the ballnut over the tube making sure not to knock any balls out. Pressed the tube against the ballscrew and 'screwed' the ballnut on. It ran fine but I could hear some rattling in the ball nut like before (as if there's a ball stuck in an unused circuit), so I took the ballnut off by unscrewing into the tubing and removed the tubing carefully to inspect. Found nothing, all where it should be, so again I made sure all the balls are pressed against the races, put the tubing back in, screwed the ballnut onto the ballscrew and same thing, rattling and the ballnut stops on its own when you spin it.

Any ideas what it can be? I'm almost sure the balls are where they should be and I've seen this before when I had all balls in the ballnut. If I leave 3 or so out, it runs smooth.

Regards,
dsc.

[dsc]

This is getting annoying now, I've re-done the ballnut yet again, for the n-th time I think, still it gets stuck. It seems like there's balls getting stuck in the return plate, just crammed in and not wanting to circulate. Here's two photos showing the balls all sitting nicely in the three circuits:

1072810727

and a video showing the nut stopping every few turns, you can also hear rattling and rubbing as something is getting blocked inside.

https://vimeo.com/79348257

I'm one step away from chucking this out the window...

Regards,
dsc.

[Ralph]

Sometimes, the balls are set out in groups. If you can pop it apart again, measure the balls. It may be some are slightly undersize and act as fillers.
If you can measure a difference, divide them up and insert them with the larger balls evenly spaced through the tracks.

[JAZZCNC]

Sounds like you have missing balls to me.?

[dsc]

I've popped it apart 50 times or so already, so one more won't make a difference. I'll see if it's all the same or whether the diameter is different on some of them.

I have 85 balls in the nut, the max capacity is 92-97, so I've lost 7 or more somewhere, although according to Gary (Zapp) they never load the nuts full to the brim. I've definitely lost a few somewhere as I've dropped the retention tubing at one point and the balls came flying out.

I've realised the return plate can go on in two different ways, so I've rotated it 180deg and it made things better, only to get stuck under load. I've assembled the Z-axis, popped the ballnut on the ballnut support and tried moving it, it crunches ever few turns and something definitely gets blocked. If I lay the Z-axis horizontal, nothing gets stuck as the ballnut is not loaded. I took a hit and ordered another ballnut, so hopefully that will end this nightmare.

Regards,
dsc.

[dsc]

Turns out RM manged to deliver the new ball nut today, tried it a second ago, it's worse than the previous one. Seriously WTF? the new one refuses to screw onto the ballscrew to start with, I've used some grease to make sure it goes on smoothly, but it crunches, blocks, jams and fails to rotate with ease. This is along the whole ballscrew which is 150mm, I've tried screwing it on with the mounting base pointing upwards and downwards, doesn't make a difference. I'm lost as to what it is, especially since this new ballnut has less balls than the one I'm using, I've got 85 int he old one and 81 in this one (27 per circuit).

Argh...

Regards,
dsc.