Re: Which end to fix...

Surprisingly, tapered roller bearings can be quite cheap, especially
if they are used in automotive applications (Small wheel bearings);
and best of all, you can adjust the play to suit your liking.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Henrik Olsson" <henrik-
olsson@...> wrote:

>
>
> Les, Jon,
>
> Thank you for your replies, just what I was hoping to hear!
>
> The ballscrews are 32mm dia, 5mm pitch, there's a 2:1

beltreduction and

> depending on what servodrive I end up with I can get between 4-8Nm
> continous from the motors which, if my math is right, will give 10-

20kN

> of thrust that the bearings will have to support (less losses).

Not that

> I think I'll need it but that's what I've got so that is why I was
> considering tapered rollerbearings.
>
> Maby I'll rebuild it in the future but for now I'll keep it as it
> is...one problem out of the way, now on to the Y-axis...
>
> Thanks guys!
> /Henrik Olsson.
>
>
> >Henrik Olsson wrote:
> >> High guys,
> >>
> >>
> >>
> >> Got a manual machine converted to CNC by one of its former

owners. It's not

> >> in operatable condition but I'm slowly getting there. My

question is

> >> regarding the ballscrew supports.
> >>
> >>
> >>
> >> As it is now the X-axis screw is axially fixed at the NON

driven side with

> >> two ordinary thrust ball bearings on opposite side of a

shoulder in a block.

> >> The driven side is supposed to be floating axially and

supported radially by

> >> a needle roller and either a standard deep groove ball bearing

or a roller

> >> bearing to take the load from the belt tension - at least that

is what I've

> >> been able to figure out so far.
> >>
> >>
> >>
> >> Qustions:
> >>
> >> 1) On just about every drawing I've ever seen of mounted

ballscrews the

> >> driven side is fixed and the non driven side is floating

(usually). So what

> >> are the drawbacks of having the non driven side fixed as

they've done on

> >> this machine? Can I leave it as it is or should I rebuild it so

that the

> >> driven side is fixed (if possible)?
> >>
> >I don't see any reason to change this. It really makes no
> >difference which end is fixed. The two bearings at the driven
> >end should support the screw against the belt load.
> >>
> >>
> >> 2) What about the thrust bearings? I'll probably add a deep

groove ball

> >> bearing to the fixed side to gain radial support since the

thrust bearings

> >> are meant for that but except of that, can I keep it like it is

or should I

> >> go for angular contact or tapered roller bearings as "it's

supposed to be"

> >> (means I have to fabricate new bearing blocks)? Buying special

ballscrew

> >> support bearings is not an option at the moment so if I'm

changing it'll

> >> have to do with standard 72xx series A/C's or tapered roller

bearings.

> >Tapered roller bearings seem like extreme overkill. Angular
> >contact bearings would be an improvement, but unless you luck
> >into some at surplus prices, I doubt it would be worth the

expense.

> >
> >Jon
>