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

Would it be considered as practical to fit bellows front a back on a
ball screw in order to improve protection. Has anybody done it.

Regards
Phil

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Tony Jeffree <tony@...>
wrote:

>
> At 03:14 29/06/2006, you wrote:
> >How is any thread or mechanism immune from contaminants without

some sort

> >of shielding/wiper system? Manual machines with acme's and

handcranks

> >stiffen up occasionaly when debris is pulled into the Acme nut.

It remains

> >that way until running it back and forth clears it. Same as

debris in a

> >standard hex nut, it locks up. I've even had mic's tighten up in

dusty

> >environments. All the ballscrews on my machines have wipers on

them. Just

> >a UHMW plate that locks into slots in the ballnut. Also,

bored/threaded to

> >fit the ballscrew.
> >
> > Just curious what the "Advantages" are to an Acme screw.
>
> I think you just described them pretty well. No thread is immune;

some cope

> better than others. You need far less contamination to mess up the
> operation of a ballscrew than a Vee or Acme screw. As you say, you

*can*

> clear an Acme nut that is clogged with debris simply by running it

back and

> forth (maybe with the assistance of a bit of light oil/kerosene

etc. on the

> screw); if you contaminate a ballscrew the fix is generally more

involved,

> requiring stripping down the nut and re-assembling it afterwards.

Yes,

> wipers on a ballnut can help, but they are not a complete fix -

fine swarf

> gets past the wipers. A friend of mine converted a mill using

ballscrews

> fitted with the manufacturer's standard wipers on the nuts; he

uses the

> mill mostly for clockmaking stuff - machining leaded engraving

brass. The

> swarf that this generates gets everywhere and finds its way past

the wipers

> very easily; he periodically has to strip the machine down and

clean the

> leadscrews/nuts to keep them operating smoothly. I suspect that

with Acme

> screws he wouldn't have to bother.
>
> On my own Taig mill, (Vee thread, not Acme, but same general

principle),

> the Z leadscrew is exposed at the bottom and regularly gets

covered in

> swarf from whatever I am machining at the time; however, the

wiping action

> of the nut means that I have never had to disassemble/clean it. I

very much

> doubt I could say the same if it was a ballscrew.
>
> Regards,
> Tony
>