Re: [CAD_CAM_EDM_DRO] Re: Knee for z-axis control?

I'm just on the outside looking in but we had a BP
clone ( I think it was called X-Cell) in my familys
shop when I was a young. It had a tape reading machine
connected to very larg steppers. (I think it was a
'70s machine) It had the Z motor on the knee.


--- R Rogers <rogersmach@...> wrote:

>
>
> doug98105 <DougR@...> wrote:
> --- In CAD_CAM_EDM_DRO@yahoogroups.com,
> "pondindustrial"
>
> 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
>
> Mazak and others traverse the whole powerhead on
> dovetail ways for Z with .0005 reliable
> repeatability globally within the envelope. They
> have no quill at all. Okuma and Howa refridgerate
> the quill so it will remain the right size and
> tight (fighting the deflection of an extended quill)
> . I wonder why they use such unorthodox methods?
> Maybe someone should call and tell them its
> nonsense....
>
> Ron
>
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