Re: Knee for z-axis control?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "pondindustrial"
<pondindustrial@y...> wrote:

> Hi all,
>
> I will be retrofitting my Bridgeport mill soon and know that some
> have used the knee for z-axis control. Does anyone here have any
> experience with this method? If so, what should I take into
> consideration if I decide to go this route? The mill has a 9" X

48"

> bed.
>
> Is a counterweight to offset some of the lifting load preferable?
> Did you use the original acme screw/nut, or retro with a ballscrew?
> What would be a reasonably sufficient drive in terms of motor

torque

> and gear reduction?
> What are the pros & cons of using the knee opposed to the quill?
>
>
> Thanks, Eric

To my knowledge there are no commercial CNC knee mills (B'port clone
types) with the Z on the knee. Ever wonder why? You would think
that at least a few builders of CNC machines might use this method
if it had some merit.

In spite of the apparent success of some conversions mentioned here,
to me it seems like total nonsense to have that much mass jumping up
and down at traverse rates we normally expect of a CNC mill.

Just my $.02,

Doug