Re: What makes a machine CNC ready?

Steve Blackmore and Marchant Dice may have gotten their units in a
bit of a muddle. Ball screw tolerances in millionths of a meter per
300mm according to my reference http://www.korta-
sa.com/catalogo/02gama.htm are:

DIN,ISO - IT1=6 IT3=12 IT5=23 IT7=52
JIS - C0=3.5 C1= 5 C3=8 C5=18 C7=50

This would make a DIN/ISO grade 7 approximately 0.002 inches/12
inches which of course is not as tight as a grade 3 which is
approximately 0.0005 inches/12 inches.

I think the error stems from the fact that the Marchant Dice website
uses the term "um", which appears to be thousandths of a meter per
300 mm when defining ball screws but millionths of a meter when
defining nuts. The ball screw page quotes the correct inch tolerance
but, assuming "um" to mean millionths, then they seem to have
incorrectly shifted the decimal place 3 places to the left when
quoting the metric equivalent.

Regards
Phil

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Steve Blackmore <steve@...>
wrote:

> There are GOOD rolled screws out there and they are not that

expensive.

>
> 0.001 per foot is not that precise, it's grade 3. That's 25.4um per
> foot, the screws I use are 0.052um per foot (grade 7;) and are

the ones priced here.

>