Re: Ball Scres from McMAster

Dave,

You're victim of something I just posted--and have previously
mentioned MANY times here in CCEd and other DIY-CNC groups.

Most ballscrews are made for moving things that are heavy, NOT for
moving things precisely.

Therefore, the high mechanical efficiency is MUCH more important
than the finish or other positional errors which may/will be found
on "cheap" ballscrews.

The tradeoff in using a cheap screw is what you've written about.
Since McMaster is not selling these based on their use in CNC
machine type applications(they'll sell you different screws for
that), you cannot always expect to get a CNC-grade screw from them,.
and may have to accept one good enough for postioning a large
satellite dish, or opening a supermarket door, etc.

Like a box of chocolates, you never know what you're gonna get when
ordering a cheap 5/8-5 BS from mcmaster. some get lucky. many do not.
most don't know the difference between ballscrews made for CNC
versus those designed for their load carrying, friction-minimising
performance.

Hope this helps,

Ballendo

P.S. Often you will get better positioning ACCURACY from an acme
screw than from a ballscrew. (When you have a budget that is equally
applied to this choice. IOW, a mid-grade acme is better than a low-
grade ballscrew.)

P.P.S. Part of the reason I've often mentioned using oversized balls
for preloading these--as opposed to double nut arrangements--is that
you can improve the surface finish at the same time as you minimise
the backlash.



--- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
<dave_mucha@...> wrote:

>
> Hi all,
>
> I just got a couple ball screws from McMaster and the finish seems
> rough in comparison to most other screws.
>
> I have some ball screws that are shiny and bright, whereas these

are

> dark and rough.
>
> The rolled screws I have from another project look much better in
> comparison.
>
> http://www.mcmaster.com/asp/enter.asp?partnum=5966K55
>
> Is there something I'm not aware of about ball screws ?
>
> If I didn't know better, I would bet that these were blanks before
> being ground.
>
> Comments ?
>
> BTW, what would one expect to pay to have the ends turned to 12mm
> about 3 inches long on one end and 1/2" long on the other ?
>
> If it does not cost too much $$, I'd have them sent out instead of
> pushing my 9" lathe to cut this stuff.
>
>
> Dave
>