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

The configuration you seem to have now will probably work ok. Keep in mind
that the majority of the radial load will be on the driven end due to belt
tension, etc. It is not as much of a problem if the screw is direct driven
through a coupler between the motor and the screw. However, with a belt you
have the actual tension of the belt plus the tension created when the belt is
driving the screw. In the case of a direct driven screw, it is often
reversed, with the thrust bearings on the driven end and the radial bearing on the
other end. The configuration you now have should work fine as long as the
bearings are in good condition and of the proper quality and tolerance.

Randy A.


In a message dated 1/8/2008 2:21:39 P.M. Eastern Standard Time,
henrik-olsson@... writes:

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)?



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.



Looking forward to your advice!



Regards



/Henrik Olsson.





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