Ball screws

[the4thseal]

I am looking for ball screws for a retrofit and other projects. I was wondering what the experiences have been with the various venders. Your imput would be greatly appreciated. I can not tell from which company to buy from. Also, do i have to buy ground screws to get good repeatability?What have your experiences been with what you are running?
TC

[NC Cams]

HIWIN sells a number of bolt in retrofit kits in both rolled and ground thread configurations.

I have them in my Bridgeport and they are phenomenal.

You will find that there are only so many "suspects" when it comes to procuring this device.

[widgitmaster]

the4thseal

Try McMaster Carr, they have a wide variety of ground screws, very fast shipping, and best of all an unconditional return system! Just mail it back to them and your payment is refunded without a re-stocking fee!

They have all types of screws, ground, rolled, 1,2,4 start, ball nuts etc...

Eric

[the4thseal]

McMaster Carr is on the expensive side. Is that the case for these things? Expensive equals good and inexpensive equals bad?

[widgitmaster]

Originally Posted by the4thseal Also, do i have to buy ground screws to get good repeatability?

Ground screws are NEVER cheap!

[the4thseal]

I know that grond are never cheap i was wondering if they are worth the money. Just how bad are rolled screws in comparison. In the real world. I know what the posted tolerances are but what are the experiences of everyone.

[NC Cams]

The error and repeatability factors of rolled versus ground screws depend on who's specs are used to roll the threads.

What HIWIN (or whomever) holds for rolled threads may or may not equate to what someone else does. You'll have to read the specs to derive the answer to that questions.

In our case, we work in tenths all the time. Rolled thread accuracies are categorically unacceptable. Your needs may vary.

If I recall properly there are even two levels of ground thread accuracies. Again, check it out (www.hiwin.com is the HIWIN site if memory serves correctly)

Are ground threads worth it? YES and no - it all depends on what YOUR needs are.

BTW, if you have lame drive sortware, poorly tuned drives and substandard ball screw support bearings and/or resonating motors, the best ground screws in existance won't make up for component deficiencies elsewheres.

[fpworks]

A standard exists for the accuracy/repeatability of ballscrews. I can't remember which organization defines it, but ballscrew accuracy/repeatabilty is "classified" from Class 0 to Class 10, lower number being better. It is sometimes difficult to find some of the even number class screws, and class 1 and class 0 screws are usually made to order.

If I remember correctly, Class 0 through Class 5 are ground screws, above that are usually rolled screws. There is a transition in the Class 5-7 range where they could be ground or rolled, depending on whatever method the manufacturer needs to meet the class standard.

Commercial CNC mills usually use class 3 or better ballscrews. Beware of "zero backlash" ballscrews with a high class number. In these poor quality ballscrews, the backlash has to be "taken up" with a compensation device (like an elastomer), so the ballscrew/ballnut assembly will have poor axial rigidity.

www.misumiusa.com has some good technical references for different ballscrew classes and their accuracy and repeatability.