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

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