Hi to all
Can some recommend bearing mounting method for ballscrew and end journals in CNC machines?
When i must use both end Fix?
When one end support and one end support?
when one end fix and one end free?
In cnc machines what should i us? FIX or Support ?
Hi, in practically all machinery using long drive shafts it is common design to fix one end at the drive point with two angular contact bearings back to back and allow the other end to "float" axially, that is it is rigidly attached in a housing attached to the machine body with a radial ball race that is allowed to float end wise in the housing to allow for thermal creep in the shafting.
Using a relatively flexible framework it would be imperitive to have the end bearing in the end floating mode to allow for movement in the framework.
In all cases of long shafting drives the free unsupported end mode must be avoided at all costs.
You can (but not always) find free end unsupported mounting modes in crosslide feed screws on lathes that do not rotate at high speeds.
Milling machine X axis lead screws are always supported at both ends, but only one end is fixed, the other end should float axially.
Long story short.....
It is not good design to rigidly fix axially both ends of a shaft that rotates.
Long shafting must be supported at both ends.
The drive end of a long shaft is always the fixed bearing support.
Thrust take up on long drive shafts can sometimes be at either end, but on one end only.
BTW, the first Photobucket pic with both ends having rigid axially mounted twin back to back angular contact bearings is practically impossible to achieve.
The second photo is the most generally used design.
The third photo has no thrust capability and will rapidly develop end movement axially.
The last photo is the design that should be avoided at all costs or shaft whip and destructive vibration will occur, but is not a problem for slow moving short length shafts.