Re: [CAD_CAM_EDM_DRO] Re: Max feedrate of ball screws?

dgmachinist wrote:

>--- In CAD_CAM_EDM_DRO@y..., "Robert Campbell" <bob@c...> wrote:
>
>
>>Seth,
>>
>>The current trend is to go to a rotating nut. The ball screw is
>>
>>
>then fixed
>
>
>>at both ends. Some machine go up to about 3,000 inches per minute.
>>
>>Bob Campbell
>>
>>
>
>
> Bob,
>
> How in the good lord's name do I make a rotating nut? It's a
>moving gantry..... Any ideas? Why is it different when the nut
>rotates? Vibration?
>
>

Long, thin shafts tend to 'whip' at high speeds. This can be dangerous,
or just ruin the screw.

The nut is mounted between a pair of tapered roller bearings or angular
contact bearings to
constrain it axially to the carriage/gantry. It is mounted so that it
rotates exactly on
its axis. A motor drives it generally through a toothed belt. This is
how the Bridgeport
BOSS series of mills did their X axis, and they only had a 40" screw
about 1.25" dia.

And, yes, it IS a complex mechanical part.

Jon


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