Re: [CAD_CAM_EDM_DRO] Doesnt ANYONE have this drawn up??? was: John's CNC plans???

Kim Lux wrote:

>I highly disagree with using existing parts.
>
>First of all, the bearings used on the ends of ACME screws generally
>aren't the sort that would be used on a zero backlash ballscrew setup.
>The runout, etc. on them is not suitable. In my opinion they need to be
>replaced with a more suitable bearing, like a 7302, a precision angular
>contact bearing.
>
>Once you realize the need to replace those bearings, the existing
>bearing holders are useless. Making new bearing mounts also allows the
>motor to mounted for direct drive.
>
>
>

The XF-12 bearings in a REAL Bridgeport screw mounting bracket
(Y axis, and the left X axis) are a matched set of spacer-preloaded
bearings, and I have tested them, and found them to be BETTER at
axially constraining the leadscrew than the angular-contact bearing pair
in my high-precision CNC axis drives. (Due to the size of the ballscrews
I used, I couldn't use the original bearings.) But, there was NOTHING
wrong with them, and they would be fine for a ballscrew installation.
Now, I can't vouch for the bearings in a Rong-Fu or some low-budget
bridgeport clone from China. Undoubtedly, they are not of the same
quality.

>Some other thoughts:
>
>a) convert as large a machine as you can. The speed with which things
>can be done on a CNC machine are only limited by the cutting power, so
>bigger = faster.
>
>

I wholeheartedly agree with this, but not only for the power reason.
A larger machine is almost certainly stiffer, and therefore can be more
accurate. Also, the larger machine can accept jobs that the smaller machine
has to do in several setups, thereby compromising accuracy.

>b) don't overlook coolant and chip handling. Coolant is an absolute
>necessity on these machines because the cutting rates are easily
>adjusted via feed override to be high. Chips will accumulate faster
>than you can imagine when running multiple parts and high cutting
>speeds.
>
>

Yup, this is also true. And, I always want to point out that keeping the
workpiece cool can improve accuracy, and prevent the dreaded
"ball up" of aluminum on endmills.

Jon