Dont know which size ball to use to preload ballnut

[maxboostbusa]

Ok I have my Roton Ballnuts in now and removed all the balls from one. They are for .631x.200 Ballscrews. The nut contained 67 balls and I was figuring on 1 or 2 sizes of balls if they used spacer balls. Here is what I measured with my micrometer.

Quanity mm size inch size
12 3.09mm .121653"
23 3.10mm .122047"
18 3.11mm .122440"
5 3.12mm .122834"
7 3.13mm .123228"
2 3.14mm .123622"

Now in giving that the total difference between the largest and smallest balls are .001969" which would be the best sizes to look for to remove as much backlash as possible from a rolled ballscrew? Thanks in advance.

[maxboostbusa]

Does anybody think that .125 diameter balls would work? Or should I get some .1240 and .1245 and try them or all of the above?

[Pres]

Neither!
Consider getting a 2nd ball nut and "preloading" them that way.

Having balls that are snug on BOTH sides of the groove is a lot more problematical than having them run on just one side of the groove.
Less drag too. - And easily adjustable for wear.

fwiw,
Pres

[maxboostbusa]

I had originally thought about doing that but short of re-engineering the cross slide I would loose to much travel or have the ballscrew very open to chips and coolant. If I cant get the backlash to a reasonable level by preloading the nuts then I will go the more elaborate route. Thanks.

[skmetal7]

I plan on preloading my ballscrews too. I just got mine and they seem to have about 0.004" backlash in them, I haven't measured the ball sizes yet but has anyone preloaded nook ballscrews before? and what size did you end up with that removed backlash?

[LeeWay]

These are about the same sizes I measured in one of my NSK ground ball screws. I only measured two sizes in it though. 3.09mm and 3.14mm. I was looking to try and locate new balls should I ever need them. Mine appear to have no backlash that is discernible. I would think that you could still use the smaller balls as spacers and just get the new larger sizes. In mine, I think 1/8" balls would be too large. Too much pressure is not desirable. Probably worse for wear than too little pressure or preload. I think it would be best to find a source balls that are exactly 3.14mm. Then use the 3.09's and 3.10's as spacers. Your would then be preloaded exactly like mine are.
I checked Mcmaster, Ebay and a few other ball bearing sources with no luck though. They all seem to have 1/8" balls though. Let me know if you or anyone has any luck locating these precision odd balls. I would be interested in getting some to keep on hand.

[maxboostbusa]

Tool Supply on Ebay and http://www.precisionballs.com are 2 places I know have odd size balls.