here's somebody on ebay selling the 5/8 diameter 5tpi ballscrews like you can get from mcmaster carr only hes selling them with oversized balls in the ballnut.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=0&item=3877296062&rd=1&ssPageName=WDVW
He claims that they have zero backlash because of this. They probably do have zero backlash but what I though was interesting is he gave the diameter of the larger bearings that he uses. Provided hes not lying he may have just given away the secret to make those ballnut/ballscrew combination an easy fix for making zero backlash. the information he provided is ....

"This brand new Thomson ballscrew assy is preloaded to zero backlash with oversized balls that are calibrated to .0001". The custom balls make contact on all four points of the gothic arch.

Ball circle diameter: .631

Pitch: .2 (5tpi)

If you need a shorter length or require end maching, please contact us for a quote. To quote for end machining, you need to send a drawing by scanning it or sending it as a JPEG.

For more CNC products see homeshopcnc.com

CA residents pay sales tax.

Check out my other items for more CNC components. "

So what do you all think? Is it as easy as buying the oversized balls instead of trying to preload them with a spring? Where would you get those diameter balls?

shouldnt have been so hasty that # is the diameter of the ball nut not the bearings. Those would be big bearings! oh well. wish I knew what size of bearings he was using It would make things a lot simpler

Easier to preload then trying to find the right sized balls....*smile*

The fellow is selling rolled screws, which is why his price is where it is. His max. length is 70 inches if I remember correctly. He's had people email him asking if it's normal for the screw/nut they bought to make "crunching" sounds. Makes me wonder about the "oversized ball" approach.

Makes me wonder if you could improve the quality of such a
screw/nut combination by using some very fine lapping compond
and exersise the nut over the entire length under motor power
for some 30 minutes.
Then take everything apart clean, scrap the balls used and reload
new ones.
I think it would be likly to cause uneven wear on the balls because
if they bind momentaryly it will create a flat spot on that ball.
I would expect the effect on the screw and nuthousing to be very positive.
Well just some thought.
In general I would consider such a arangement to be much more sensitive
to contamination of dirt with the effect of more liklyhood to binding.
Most of the people I know of that have used oversize balls sucessfully have
still a small amount of backlash left in there.

I've heard when using oversize balls that you need to alternate tham with standard size balls so there is some room for them to actually roll. Otherwise, they'll just slide around.