Re: [CAD_CAM_EDM_DRO] Re: Z axis

mjf462001 wrote:

> --- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> > mjf462001 wrote:
> >
> > > Hugh,
> > >
> > > Thank you for the link. I am still not sure weather
> > > I should drive the quill or the knee. When I get around to making
> up
> > > my mind I will at least have some pics to reference to.
> >
> > If you use the machine to drill holes, or if you have some slack
> > in the vertical ways for the knee, like mine, then I think you
> should
> > go with the quill. My knee sags out, toward the operator, when you
> > lower it. I can't tighten the gib because there is a worn spot on
> the
> > ways.
> >
> > Jon
>
> John
> I saw a pic of Dan's setup. The way he drives the knee, I would say
> it looks pretty rigid!
>
> Without having to do the math I wonder how much torque a guy needs
> so he wouldn't have to gear down (slow down) the z axis drive.
> The mill is new and without any wear.

I'm not saying it isn't rigid, just that you are moving a LOT of iron to
poke
a 10 gram drill bit into a workpiece. On a Bridgeport Series-I size
machine,
you are talking about moving about 1000 Lbs of iron up and down every
time. It certainly will work, but it may cause much more rapid wear on the
knee slide. You should note this is the most highly stressed way on the
machine, as the weight is completely off to one side of the slide. Worse,
it puts the load on the dovetail, rather than on the flat!

I think it is unreasonable to try to CNC the knee without a ballscrew
retrofit. And, after a ballscrew, you'd need a safety brake to prevent
the table from dropping when you go to E-stop, or lose power. A
reliable counterbalance, either weights and pulleys or gas springs,
would help out, but then you'd definitely need a ballscrew, or the
backlash would show up, without the knee weight.

Jon