RE: [CAD_CAM_EDM_DRO] CNCing the knee axis...

On Wed, 2003-09-24 at 09:44, Dan Mauch wrote:

> I have my enco 8X36 mill with a 600 oz in servo motor driving a 3/1
> ratio timing pulley which in turn runs the knee acme leadscrew. With
> this arrangement the weight of the knee keeps the slop out of the Z
> axis.

The question is, does the knee jib keep the table perpendicular with the
spindle ? I haven't tested ours yet...

> Using a 3/8" end mill I can bore a 1.000 hole usually within
> .0005. (I have zero backlash ballscrews on the XY axis)
> While it is true that I cannot cut as heavily using the knee as I could
> by locking the knee and using the quill, I can still take respectable
> cuts.

Why is that ? One should be able to run a tight gib on the knee. It
has lots of surface area.

> The reason that adding a servo to the knee, is that in my opinion,
> it is much easier that building all the stuff for the quill.

The thing I don't like about the quill is the limited travel. *If* you
get 5", and you need to bore 3" deep, you only have 2" for clamp
clearance. It gets worse once you consider longest tool/shortest tool
clearances too.

> I did not
> use any air springs on my knee but I am happy with the speed that I get
> on the Z axis. I could probably double the speed if it the knee was
> counter balanced.

Which motor did you use ?

> I guess it depends on how much work you want. Putting a ballscrew and a
> servo on the quill would be the best solution but in my case putting the
> servo on the kneee was the best compromise.

If the slop in the knee slide can be eliminated, I don't see anything
wrong with powering the knee. BTW: I pull the cover off the way and
there is a gib adjustment on our mill.

>
>
> -----Original Message-----
> From: Kim Lux [mailto:lux@...]
> Sent: Wednesday, September 24, 2003 7:40 AM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: Re: [CAD_CAM_EDM_DRO] CNCing the knee axis...
>
>
>
> Does this mean that CNCing the knee is not a good thing to do ? Should
> I just CNC the quill and leave the knee alone ?
>
> Kim
>
>
>
>
> On Wed, 2003-09-24 at 08:19, Weyland wrote:
> > Hey Kim~!
> >
> > On Wednesday 24 September 2003 09:17 am, Kim Lux spake:
> >
> > > I've got two concerns with controlling the knee:
> > >
> > > a) does the knee remain square to the machine when not locked ? Ie
> > > is the knee designed to be an axis feed, ie moved up and down
> > > without being locked ? (my friend tells me no...)
> >
> > Your friend is absolutely correct.
> > A knee *will* move without it being locked.
> > You can verify this by setting up an indicator on the
> > table, against the quill, and locking and unlocking the knee.
> > On some machines, you will see it move as much as .010".
> > On my Bridget, it moves just under .001".
> > (and I probably need to adjust the gib...)
> >
> > > Our mill does not have a gib
> > > adjustment on the knee.
> >
> > Are you sure?
> > Just about every one I've ever seen has a gib...
> >
> > Check under the way wiper.
> >
> > Best,
> >
> > Weyland
> >
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--
Kim Lux <lux@...>