RF45s and clones: DON'T.

We've CNC'd an RF45 clone (Grizzly G0519) and are quite disappointed
with it. The CNCing works fine. The problem is the rigidity of the
head when milling with significant cuts. The head on these mills hangs
on the Z axis way with a short (8") gib. The head is fairly heavy, ie
150 pounds. That whole weight is levered off of the short gib. The
result is significant head flex when machining parts.

We've put a dial indicator between the head and the table. We can
induce 10 or 20 though of movement between the two by pulling on the
head. By contrast, we cannot induce any movement on a Bridgeport clone,
which is obviously a turret mill. This measurement was done with the
knee unlocked. A mini Bridgeport clone might be twice the price of an
RF45/clone, but it is 3x the machine an RF45 is.

We will be keeping our RF45 clone. We'll use it for light duty
machining operations. We are in the process of CNCing our Bridgeport
clone, by motorizing the knee. I've got the Z axis drive done.

BTW: if you CNC your RF45, I highly recommend using 3/4" ballscrews for
the X and Y axes.

Kim

On Sat, 2003-10-18 at 22:38, Thomas E. Jones wrote:
> Hello:
>
> I'm CNC'ing my RF-45, and starting with the ball screws.
>
> It seems most are using the 0.631 ball-diameter (0.615) size
> screws from McMaster Carr or Reid Tool. These nuts are under
> $25.00 each, and the screws are cheap. The next size
> (3/4 inch or so) is more than twice the cost.
>
> Is this really big enough? My ACME screws that came with
> it are about 7/8 (or 1", I'm not certain.) I've heard the
> controversy saying that these thin screws are only good
> for very short shafts (like lathe z-axis) but not only are
> larger more expensive, but they don't fit in the allowed
> space well.
>
> Does anyone with "experience" have comments. I know, in a
> perfect world, I'd aim for 1" ball screws.
>
> Also, is there any good online source for single-quantity
> ballscrews and nuts other than the two above sources? I
> like web sites that actually have prices, and will sell
> without a minimum quantity.
>
> - tj.
>
>
>
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