How to get the balls back in a ballnut?

[Shinobiwan]

A new nut from Chai is only £16 including air mail. A lot cheaper than I thought it would be. Might just order a new one but will have a quick bash at getting them back in before that.

[Robin Hewitt]

If you make a ball insertion tool it's easy

OTOH, making the tool is a right PITA.

[Jonathan]

If you make a ball insertion tool it's easy

Could've told me that an hour ago, :



Actually it wasn't so bad with the big magnet, but if you don't have a suitable magnet then your way is a lot cheaper. It's a double start nut, so having 6 return tubes made it more difficult for the magnet to retain the balls, however they were sufficiently well held for me to be able to pour oil through the nut to clean it before putting back on the screw.

Earlier today I was removing the other nut from this ballscrew, holding it vertically and meanwhile the other nut decided to start spinning due to gravity and drop on the floor, so then I spent a while scrabbling around with the magnet finding the 51 balls. You can work out the number of balls per track, or at least get a reasonable idea, by simply measuring the pitch diameter and using that to find the circumference (accounting for the fact it's helical) and dividing by the measured diameter of one ball, i.e. ((pi*16.803)^2+10^2)^0.5/3.167=17 for this nut.

Shinowbian: I've got a spare RM1605 nut, so if you need one sooner than Chai can deliver then we can do a swap so long as you have all the balls.

[Shinobiwan]

Managed to get them back in last night. Spent about an hour fumbling around with the first circuit of bearings then hit upon a trick and the remaining two circuits were done in about 10 minutes.

Only problem now is the ball nut feels a tad notchy at irregular intervals when turning. Its not binding tight just a moment of slight resistance then it free's up. At first I thought I'd gone and got a ball somewhere it shouldn't be so stripped it down again and took a more methodical approach. Cleaned everything again, separated the 48 bearings into 3 piles of 16 and carefully loaded them back in.

Still the same notchiness... hmm. This was a Strike CNC supplied ballnut/ballscrew and I can't say for sure if it wasn't like that before I spilled the bearings. Maybe I've knackered it up with playing around but I like to think Strike CNC, struck again!

EDIT: Seems to run smooth if you load the ballnut. Strange. Any thoughts?

[Clive S]

I have just come across this Linearmotionbearings C7 Ballnut Flipping and Repacking - YouTube as it shows in the vid how to re fill ball nuts etc. Clive

[John S]

That's assuming you have the same diameter at both ends of the screw.
If he'd just used a tube, no flanges and a couple of winds of tape round one end it then possible to use the same loading tube to switch to the same end. Just swap the 'safety' tape over.

[Ricardoco]

Haha! Oh yes!

Yep I'd been warned well in advance by Jazz that unscrewing the ballnut off was a big no no unless your a sadist.

So like yourself wilfy I wasn't curious enough to just wind the nut off and look inside. No, instead my accident was more spectacular. This was on the Z, I had no bed to limit Z travel and no floating end ballscrew mount to stop the nut either... cue me playing with motor tuning - a nippy 8m/min with slow slow acceleration. Wound it up to a good speed and then watched in horror as it slowed down like a snail all whilst smashing the Z 'up' button on the keyboard to no avail! Moments later, the Z axis front plate is off the machine and its raining ball bearings! lol Good times.

Humans... we are constantly finding new and inventive ways to f$%k up!

Ps. Thanks guys. I'll have a shot at this I think. Worse that can happen is I fail and go order a new nut.

Ive read this three times and each time it gets funnier, I can only imagine the expression of desperation and shock on your face as you watch your Z front plate part company with the back plate, and the disbelief as the balls cascaded all over the place.... PERFECT!!

Rick