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

On Mon Oct 20 07:31:01 2003 Kim Lux wrote:

>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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