Re: [CAD_CAM_EDM_DRO] RF45s and clones: DON'T.

On Mon, 2003-10-20 at 10:00, Jerry Kimberlin wrote:

> Kim Lux wrote:
>
> >I actually think that makes it worse. The short gib and the long overhang is just
> >a very poor design.
> >
> I read your posts and have no quarrel with anything you say. But I
> think there must be something wrong with your G0519 if it moves that
> much. I have one and I get flex, but it is only 0.003" for a 50lb pull
> on the head..

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. However, even with the gib
totally locked we still see flex. Grizzly is supposed to send us a new
Z axis slide, but (I think) they've found all the slides have this
problem.

Are your measurements with the gib locked or loose ? ie can you move
the head up and down via the crank ? Our gibs are loose (ie not locked)
when we are taking this measurement and machining.

> There may be more if you pull on the quill instead of the
> head, but that is normally locked during cutting.

We lock the quill during cutting.

> I would be interested
> to know how you accomplished the CNC on the Z-axis?

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.

In operation, the Z axis ballscrew holds the head in position while
milling. The ballscrew setup we use is very solid.

> Since these mills are a parts kit and not ready to run, you have to
> remove all the gibs and grind them flat on a surfact plate.

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.

> If you
> haven't done that, you won't get the head gibs tight enough to eliminate
> as much of the movement as possible, nor smooth enough for the head to
> rise and fall easily.

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.

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.

Kim

> JerryK
>
>
>
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--
Kim Lux <lux@...>