Re: [CAD_CAM_EDM_DRO] Re: rolled ball screws

Hi Les:
I found your comments on this subject very interesting.
I just dealt with a Hiwin dealer, regarding preloaded ballnuts in rolled
screws, and was told...NO WAY, CAN'T BE DONE!!!
The reason given, was that the inconsistencies in the rolled screw would
make the screw run so rough that most of the benefit of ballscrews would be
lost.
I was told they'd run hot, that they'd bounce all over the place, and that
they'd alternately run loose or tight depending on where I happened to be on
the screw.
I was also given to understand that the service life was going to be
pitifully short.

My motivation for getting into this subject in the first place is that I've
got a little sinker EDM that uses a Moog valve on a hydraulic cylinder to
drive the ram.
The hydraulic pump is incredibly noisy, and the ram lock on the machine is
starting to drift, so I am having increasing problems holding tolerance on
sideways burns with the orbiter.
I intend to replace the hydraulic ram with a stepper driven ballscrew.
I needed a short ballscrew with a rotating nut, because I don't have the
space in the machine frame to run a conventional rotating screw, and this is
where the discussion regarding rotating ballnuts and rolled ballscrews and
precision began.

Do you think I may have been bullshitted in order to upsell me a ground
screw?
Any comments from you and other list members will be eagerly awaited.
Thanks in advance

Cheers

Marcus

----- Original Message -----
From: "Les Watts" <leswatts@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Wednesday, January 08, 2003 6:43 AM
Subject: Re: [CAD_CAM_EDM_DRO] Re: rolled ball screws


> The HIWIN ballscrews I mentioned are rolled and supplied
> from the factory with oversize ball preload at about 5%
> max dynamic load. I did not put them in. The drag torque
> is about 100 in oz.
>
> As far as I know they are the only manufacturer offering
> this type of preload on a rolled screw. All the others had
> to use a soft spring to preload double nuts, and the stiffness
> was much too low for my application. Of course most
> have stiff preload ground screws, but they are very costly.
>
> I did visit the HIWIN US headquarters and saw them putting
> in balls for special order preload amounts. A guy there had
> a bunch of balls sorted into small bins for size in one micron
> increments. He put them in with tweezers. I wouldn't want
> to try it.
>
> Les
>
> Leslie Watts
> L M Watts Furniture
> Tiger, Georgia USA