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

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