Re: [CAD_CAM_EDM_DRO] Re: rolled ball screws

Hi Les:
If they've been giving you ground screws all this time by mistake, you
will have my undying envy forever.
I was just quoted a price for a 15" length of 25mm x 5mm pitch ballscrew
with preloaded nut (not rotating nut-which is actually what I wanted...but
nevermind).....wait for it...690 bucks US!!!
I don't even want to think what a 10 foot run might cost, especially in the
bigger diameters.
I'm bursting with curiosity about what I'm going to get quoted for the
rotating ballnut.
It's a special order item (not a good sign I believe), and so far, no dice
on price or delivery.

On another note, how are you making out with your custom furniture making
enterprise?
Do you have recent pix posted on your site.
I don't believe I've ever seen photos of your legendary killer gantry mill.
Cheers

Marcus

----- Original Message -----
From: "Les Watts" <leswatts@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Wednesday, January 08, 2003 11:33 AM
Subject: 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.
>
>
> Hello Marcus
>
> Hmmm well HIWIN does it (they say)and I have used them for several years.
> I was told by other manufacturers that it could not be done, at least by
> them.
>
> At the time I was specifying ball screws for a large corporation so we
> had application engineers come in from all the major manufacturers.
> Just about all recommended ground ballscrews for any cnc use.
> But I wanted to see a stiff preloaded rolled screw. I could software
> comp inaccuracies and I just didn't see any major technical problems
> with someone being able to make them. Neither did any of our staff.
> And I didn't buy the ridiculous price of ground screws. We did a lot
> of that kind of stuff (large scale thread grinding) and it is not that
hard.
>
> Then HIWIN told me about their "precision rolled" product. They were
> close by so they invited me to tour their facilities. That is where I saw
> them fitting oversize balls.
>
> I was very concerned in that I could not find a preload drag torque
> specification for that product line in their literature. They said they
> didn't have one published. I thought "uh oh". Not good. But then
> we just took one out and I hand rotated the nut and it felt super
> smooth. Later I hooked one to a dc motor and monitored current
> while driving the nut back and forth. The current (and therefore torque)
> varied no more than a few percent!
>
> So I use them. I think HIWIN has great products, but their sales
> and engineering staff here are kind kept in the dark. They don't
> have the literature and knowledge of their product lines. Often
> they don't even know what they have stocked other than it's there
> and the part #. So I am not surprised that a rep is confused.
>
> As far as whether this preload can be done _reliably_....
> I think it is just a matter of having the right effective spring
> constant in the nut housing so it can expand without imposing
> huge loads on the balls. Four point contact ball bearings are
> commonly sold by many manufacturers and used a lot.
> It is also a matter of keeping lead pitch consistent.
> The HIWIN screws I have measured are remarkably good
> as far as pitch accuracy.
>
> Here is one possibility- perhaps they have been mistakenly selling me
> GROUND screws all this time! Maybe I ought to run up there and
> get a truck load... ;^)
>
> Les
> Leslie Watts
> L M Watts Furniture