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

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."

>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.

>Are your measurements with the gib locked or loose ?
>

It makes no difference on mine. The flex seems to be about the same

>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. Was that very difficult?
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. Which servo motor are you using and is it geared down?
Are you using a 1" ballscrew or what size?

>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. 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.

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.

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. 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. 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.

JerryK