[teyu]

S&A industrial water chillers have passed ISO9001,CE and RoHS approval, It is green product.

[joeavaerage]

Hi,
there are ballscrews.....and there are ballscrews.

There are two basic types, rolled and ground.

Rolled ballscrews , are as the name suggests, manufactured by rolling the thread onto a blank shaft. This is a fast and cheap method
of manufacture and these screws abound on Ebay etc. They are commonly C7 grade, that is to say they are accurate to 50um in 300 mm
and have a cyclic variation of about 30um. All-in-all rolled C7 screws are good value for money but fall short of the label 'precision', the cyclic variation
particularly. The good news is that a C7 screw, say 20mm diameter and 1m long, with bearing blocks can be had for $200-$250. They have 'oversized'
balls which result in zero backlash. The cyclic variation causes a fluctuating preload and life expectancy of a C7 rolled ballscrew is not high.

The second type of ballscrew is ground, where the thread is ground into a blank shaft. This requires very expensive grinders and is time consuming.
The entry level ground ballscrew grade is C5, 18um per 300mm and max 8um cyclic. They are preloaded, some with outsize balls, some with double nuts,
and because of the much reduced cyclic variation and consequent lack of fluctuation in preload, last well. Better grades are C3, approx 8um per 300mm, C1
and even C0's. The later two are for semiconductor equipment and CMM's, ordinary people need not apply!

The downside of all the 'ground goodness' is cost, a ground C5 ballscrew of 20mm diameter and 1m long say with two angular contact bearing blocks
will cost approx $2000! Yes that's correct about ten times what a rolled C7 screw would cost. Quite frankly I don't know what C3's, C1's and C0's cost.
It was all I could afford to get three second hand 32mm C5 double nut THK ballscrews with bearing blocks for $1000.

Overall I support the notion that good ballscrews beat ACME screws for accuracy, efficiency, backlash and life expectancy, but all of that comes
with ground ballscrews which are eye-wateringly expensive. Rolled ballscrews enjoy the same benefits but to a much much lesser degree
but are about 1/5th to 1/10th the price of ground C5's.

Depending on your accuracy expectations rolled C7 screws are great, they have proven to be a boon to low cost CNC machine makers and hobbyists
alike.

If you want genuine accuracy, consistent preload and life expectancy the ground C5's or better are required....despite the cost.

Craig

[joeavaerage]

Hi,
just as a matter of interest I have bought second hand ballscrews, linear rails and cars from:

https://www.ebay.com/str/industrialpartsshop

It may be that by careful searching and selection you can get C5's (or better) for the same or less than new rolled C7's. I did.
This outfit has been my go-to source for this sort of stuff and very very good they have proven themselves to be.

Craig

[joeavaerage]

Hi,
in fact I just had a fresh look at their site and saw these:

https://www.ebay.com/itm/THK-USED-Do...sAAOSwPWRZSm4G

which are the exact....and I mean exact same ones that I bought for my new mill.

Craig