Hello All,

First post here and would like to thank all the posters here and on CNC zone for providing a lot of food for thought.

In a mad moment, after 30 years of nibbling things out on a little Southbend with a machining vise (there was a brief interlude with a Cincinnati #2 Midget mill before a shop downsizing) , i acquired a 602 which was originally set up for 575V 3ph. My shop power is 240V 1ph.

The intended use would mainly be to support individual projects with component runs unlikely to exceed a dozen pieces or variations on a theme. Materials would be about 50% plastic (mainly acrylic), 25% aluminum and the remainder stainless, alloys along the lines of 4340 and of course mild steel.

I have about a six week window to concentrate on 3-axis functionality and would like to add 4th (indexing and continuous) over the next year or so. Given the available time frame, budget (about $5kCDN) and a need to finally get competent in C programing, i am considering going with Dynomotion Kflop +/- Mach3 and DMM "ac" servo motors.

I am still struggling a bit between BLDC and ac servos. Does it just come down to 2 vs 3 active poles of excitement and smoothness of excitation wave?

The variable speed has been removed (hi/lo gearbox retained) and the mill came with an uninstalled 5hp 3540rpm 264V(delta) spindle motor. It would seem that best approach for the spindle would be a VFD and encoder for motion feedback. If i understand correctly, the 602's were originally equipped with 1.5hp spindle motors with an option for 2hp. However, my impression from scouring the forums is that there will be torque loss at lower speed so may want to go with 3hp. The 5hp motor seems a little excessive, and there may be a good home for it in a YAM 22"Swing x 33"c-c lump of iron and ball screws that somehow found its way onto the trailer and into the shop recently.

There is, of course, a wide price range for 2 or 3hp motors with some claim of "inverter duty" capability and i am having trouble gauging what would be a practical level of motor to choose for a mill that will see intermittent use. Would it be crazy(ier) to consider a 2 or 3hp ac servo for the spindle instead of VFD and inductive motor?

Z (quill) is 6" travel with a 0.75"d, 0.200" lead ball screw on a 1:1 worm.
X is 48" max and Y 18" max with 1.25" x 0.200" lead screws and 2:1 pulleys.

Initial playing around with Kollmorgen Motioneering Engine seems to suggest peak torques of around 7-9 Nm but i am pretty shaky on what the thrust and continuous forces should be (went with a 1000 and 200N). Rapids on the order of 150-200ipm and feeds of 20ipm seem plenty to me at this time but that is just a guess. The swag approach of how hard would you lean on a hand wheel (about 10lbs @ 3" via Mariss - Servo or Stepper for CNC? - Page 2) would suggest a peak torque requirements of around 2-3 Nm.

The difference between the two sizing approaches seems to be 750-1000 W vs 400W motors. There seems to be a distinct jump in price and power supply requirements (over 100VDC or typically 3ph for ac servo drive for >400W systems) between these two in the low cost new NA market (will save ebay and alibaba for the YAM adventure). 400W motors could powered through Dynomotion SnapAmp and controlled directly by the Kflop vs going with DMM Dyn3 amps. Setting performance requirements aside, the price difference between the two approaches for 3 axis is not huge. Going with the Dyn3's would simply the power supply installation (simple 220V 1ph vs added DC supplies) but would give up the apparent intrinsic value of integrating all of the control in the Kflop.

Would anyone care to comment as to whether, for a mill of this "size" (about 3000lbs), use (intermittent very short runs but will have to tackle some tougher alloys), mass in motion (9"x48" table and weight of planned 4th axis) and age (old ball screws, presume steel on cast slides), would going with 400W motors with rated/peak torques of around 1.3Nm (180ozin) / 2.5Nm (355ozin) be a reasonable approach or would it likely end in plodding, stalled tears?

Is there enough experience out there with upgrading these types of mills to make a reasonable call or should i disconnect the ball screws and measure the table motion forces, accurately measure the tables and calculate masses as well as learn a little more about feed forces and identify more specific performance goals?

Sorry for the long convoluted post, if i am missing the boat and need to delve deeper or into other topics please point me in the right direction.

Thank you very much,