[CAD_CAM_EDM_DRO] Re: ball screw conversion

This is interesting information I had not heard before. Though I
never look at the crank collars and use a DRO instead, it can already
be tough to get the crank to stop on a thou with the acme screws.
Maybe ball screws are not the great improvement I imagine.


At 4:50 PM +0000 12-3-09, tjwal wrote:

>Bryan
>Ball screws do not work well with hand cranks. Due to their low
>friction and low tpi they are not self-holding and any force on the
>table will cause them to rotate. Unless you lock the table you
>would not be able to let go of the handles when milling. There are
>probably work arounds for this but you are still stuck with the low
>tpi.
>
>With a 10 tpi leadscrew a complete turn is 0.1" and with a 100
>division collar you can adjust to 0.001". With a 5tpi or less
>ballscrew it would would very difficult to get 0.001 manually.
>
>
>ACME leadscrews with higher friction and higher tpi are self holding.
>
>JohnW