Re: [CAD_CAM_EDM_DRO] Which end to fix...

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