B/S vs. acme was Re: What makes a machine CNC ready?

Relative to a conventional lead screw - no. Everything wears, but
ball screws wear at a rate similar to that of ball bearings. They
can last for MANY years without showing any signs of wear. Look at
all the used CNC machine tools out there, many of them have been
running 24/5 for as many as 30 years. Often, the backlash is still
less than a couple thousandths if even that. However, if they cut a
lot of cast iron, chances are pretty good they will have worn a bit
more - nature of the beast.



--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Andy Wander" <awander@...>
wrote:

>
> So ballscrews don't wear?
>
> PS Chris I think you are a pretty high-quality poster, if my

opinion

> counts for anything.
>
> ________________________________________
> Andy Wander
>
> -----Original Message-----
> From: CAD_CAM_EDM_DRO@yahoogroups.com
> [mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of lcdpublishing
> Sent: Thursday, June 29, 2006 7:05 AM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: [CAD_CAM_EDM_DRO] B/S vs. acme was Re: What makes a

machine CNC

> ready?
>
> The problem I see with acme screws is wear - you simply cannot

stop

> the wear. Sure, you can hide it - with anti-backlash nuts, but

you

> can't stop it. Anyone that has run an older bridgeport knows

about

> this. The middle area of the screw is worn more than the ends -

shows

> up as backlash. So, further complicating the issue with acme

screws

> and wear, is it is un-even wear.
>
> Some antibacklash nuts will automagically adjust for this, some
> won't. Some use springs to spread two nuts. This will certainly

hide

> the backlash, but it won't fix it - it's sort of like back lash

comp

> in the CNC control - hides it, but doesnt fix it. Back to the

spring

> loaded A/B nuts, while they do hide it under light loads, if the
> cutting forces exceed the spring tension on the nut, backlash

comes

> back into the picture again, only this time it is a problem
> under "special conditions" making it for a real nightmare to

figure

> out.
>
> I really don't think either type of screw system is immune to

chips

> and lack of lubrication like others have stated, that is just
> nonesense. Both need proper lubrication, both should be kept

clean

> from debris. Just because big chips won't get "inside" the nuts,
> small particles can and will, and those are the ones that cause

the

> damage.
>
> So, if you are okay with "hiding problems", Acme lead screws are

fine

> as long as you know they will wear and that A/B nuts will do a

pretty

> good job of hiding the wear and resulting backlash, they won't fix

the

> wear.
>
> Chris (Certainly not a "High Quality" poster)
>
>
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