Re: What makes a machine CNC ready?

So, using that information you are providing.....

Let's assume (Nasty word isn't it), that we will traverse 20" every
minute in a production machine. Production machines run 21 hours a
day and we will say it's run 5 days a week for a year...

5 (days) x 52 (weeks) = 260 days
260 (days) x 21 (hours) = 5460 hours
5460 (hours) x 60 (minutes = 327,600 minutes a year
20 (inches) x 327,600 (minutes) = 6,552,000 minutes in traverse per
year.

So, according to the two numbers you provided...

if the ball screw's are rated at 2.1 million inches, then a machine
needs to have it's ball screw fixed or replaced every 4 months

Or

If the ball screw's rated at 1 million inches, then a machine needs
to have it's ball screw fixed or replaced every 2 months

I think there is a lot of machines out there running with ball
screws LONG BEYOND their service life according to your numbers.
Heck, some of them wouldn't even make it past the duration of the
IMTS tool show according to those numbers. I suspect that
the "Sevice life" is perhaps "Time to look at it" as opposed
to "Time to fix or replace it".

Knowing first hand from practical experience in machine shops and
working for machine tool builders, I know for certain that lead
screws wear and fail much more quickly than ball screws. So, if
those numbers were even close to being accurate, you would probably
have to replace a lead screw every other day! I know that certainly
isn't the case so something sure is fishy about those numbers you
are quoting.


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Fred Smith" <imserv@...>
wrote:

>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "lcdpublishing"
> <lcdpublishing@> wrote:
> >
> > That's a pretty bold statement.....
>
> >
> > Why would that ball screw fail in 5 years? I have never seen

any

> > references published that state the life span of a ball screw is

5

> > years, 10 years, or 20 minutes.
>
> Ball screws have a rated service life. I expressed it as cup half
> empty, instead of cup half full. ;-)
>
> Some Thompson ball screws have a 2.1 million inch rated service

life

>
> I estimated this as 3 hr/wk at 50 ipm = 9000 inches per week
>
> 5 years at 50 wks per year and 9000 inches per week = 2.25 million
> inches.
>
> Several other US manufacturers rate their ball screw service life

at

> 1,000,000 inches. If you read the literature published by the
> manufacturers, you can see the detail of how they predict service
> life.
>
> Fred Smith - IMService
> http://www.cadcamcadcam.com/hobby
>