Re: RF45s and clones: DON'T.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Kim Lux <lux@d...> wrote:
> Comments below:
>
> On Mon, 2003-10-20 at 11:13, Jerry Kimberlin wrote:
> > Kim Lux wrote:
> >
> > >We are pulling more than 50 pounds, probably 100 or 150 pounds.
BTW:
> > >there is an issue with our G0519 too: the gib bolts are threaded
into
> > >the gib corners, thus they work loose.
> > >
> > Interesting. I have had no trouble with this. You just relax
the one
> > on the bottom of the gib and tighten up the top one until the gib
is
> > tightened properly, then tighten the bottom screw. Go back and
forth an
> > eighth of a turn (or less) this way until you get the
correct "feel."
>
> We can't really tighten ours properly because the thread is wrecked
from
> intersecting the corner of the gib. They've promised us a new
slide,
> but we haven't seen it <yet>.
>
> > >However, even with the gib
> > >totally locked we still see flex.
> > >
> > Yes, so do I. The flex is probably not in the joint between
column and
> > head, but in the column and base.
>
> I think it is in the attachment of the head to the column.
>
> > >Are your measurements with the gib locked or loose ?
> > >
> > It makes no difference on mine. The flex seems to be about the
same
>
> OK.
>
> > >We pulled the stock Z axis lead screw out and replaced it with a
ball
> > >screw/preloaded nut assembly. The servo motor sits atop of the
Z axis
> > >column. We counter weighted the axis by running two cables to
the top
> > >of the column and then down to 200ish pounds of weight. The
head is
> > >pretty light to move, save the drag of the gib.
> > >
> > Thanks very much for that information. You had to make a new
holder for
> > the ballscrew and one for the ballnut too.
>
> Yep.
>
> > Was that very difficult?
>
> Relative to what ? Nothing was square on the mill, so that was the
> hardest part. It works really well, head flex aside.
>
> > The acme leadscrew is not up the center of the column and a ball
screw
> > would have to be relocated about 3/4" or so to center it in the
top
> > column hole.
>
> We did exactly that. We mounted a plate across the top of the
column
> with zero backlash bearings in it.
>
> > Which servo motor are you using and is it geared down?
>
> Amatek 40VDC 600 oz in peak, direct drive. Remember it is counter
> weighted. We've got Z axis speeds of 100 IPM.
>
> > Are you using a 1" ballscrew or what size?
>
> 3/4" and it is plenty strong. That is a short screw, about 22"
long.
> We are using a 1" on the BP clone Z axis. I'd use a 1" ballscrew
on the
> Z axis of a 40" lathe too.
>
> > >This I did not know. We bought the mill complete, assembled and
ready
> > >to run (manually), from Grizzly. I *assumed* that the parts were
> > >machined properly and ready to use.
> > >
> > All the gibs are rough as a corn cob.
>
> My machinist told us that was like that on purpose, so that the ways
> will hold lube and not wear out prematurely. He was impressed with
> this.
>
> > If you just sand them wet on a
> > surface plate, you will knock off enough of the roughness to make
them a
> > lot better and then they will run a lot smoother on the X and Y
so that
> > there are no tight spots. I had to do this. I'm sure the Z axis
will
> > benefit too.
>
> I don't have the time/inclination to do this.
>
> > A lot of these machines are full of cosmolene which may or may
not have
> > casting sand entrained in it. You have to get all that goop out.
>
> We pulled every part of the mill apart when we CNC'd it.
>
> > The joint between the column and the base on mine had paint in
it. I
> > had to use a scraper to get that out, and to make sure the column
was
> > plumb before re-bolting it.
>
> Maybe that is why ours is flexing. We didn't take that apart.
>
>
> > If you have loose base bolts, or something
> > spongy in there like paint, that has to be removed. When I got
my mill,
> > I just assumed that I had to totally dismantle it and
remanufacture
> > parts of it as every machine I've ever bought from the far east
has been
> > this way.
>
> Our lathe and BP clone (Enco) were both fine. Several years of use
and
> no problems. Never had anything apart on them. I'd never buy
anything
> but a BP clone again. Not only are they smaller ie less robust,
but the
> machining on them isn't as good.
>
> > You might find absolutely nothing wrong, but you may find
> > something else. That is why these things are generally assumed
to be a
> > kit of parts.
> >
> > >I don't know what to think of that advice. When I buy a machine
tool, I
> > >don't expect to take it apart and refinish things,
Chineese/clone or
> > >not.
> > >
> > I agree. Quality will improve in time, but it hasn't as yet.
>
> > >Given that we still have flex when the gib is locked, I think it
is a
> > >machine design issue. Given the overhang and weight of the
head, that
> > >gib should be 14" long, not 8". And the column should be bigger
> > >
> > Again, I agree. My other mill has none of these problems.
>
> I wish someone made a reasonably priced bed mill with a 15 x 40
table
> and ballscrews. Gromax has nice bedmills, but they are expensive.
I'd
> liek a CAT40 spindle and a 3+ HP 3 phase motor.
>
>
> > JerryK
> >
> >
> >
> >
> >
> > Addresses:
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> --
> Kim Lux <lux@d...>