Greetings,

I am an intern tasked with building a CNC mill that has the following characteristics:

- Small machining volume (approximately 3"x3"x3")
- Need to machine aluminum at medium feed rates (about 50 IPM)
- Small material removal rate (<1 in^3 /min)
- A precision/repeatability of 0.001 is essential
- Industrial, must be able to repeat a simple chamfer operation and milling operation quickly for up to 18 hours/day
- Must be able to perform a chamfer operation on two faces, and a milling operation on one face, preferably simultaneously
- I have access to industrial mills (and qualified machinists) to machine any required components
- Budget: Up to $5,000

Design Summary:

I am attempting to modify a standard gantry-type CNC mill, but instead of mounting a spindle on the gantry, mounting my workpiece. The gantry system will then be able to drive the workpiece in 3 axis into three stationary spindles. I envision that I will have three stationary spindles, that will be running continuously at about 15,000 RPM for 8 hours at a time. Mach3 will be only be used to control the stepper motors. Due to my very small required travel lengths, I expect to be able to make my system acceptably stiff and precise using quality components and custom-milled aluminum structural members. I started an earlier thread with the false assumption that I needed feed rates of up to 300 IPM. I now realize that this is totally unrealistic, and unnecessary. After a bit of research, I've put together a Bill of Materials that represents the best of my knowledge at this point. I am looking for feedback, and a check that this project is headed in the right direction.

I will loosely be basing my design on this Instructables post, with the exception that my build will have much smaller travels.


Bill of Materials:

Category Description Qty. Price Total Website
Spindle 800 W Water Cooled CNC Spindle 220V 3 279.00 837.00 http://ugracnc.com/WATER-COOLED-SPINDLES/GMT-Water-Cooled-CNC-Spindle-0.75-kW-220V-R.html
Spindle Power Supply 2.2 kW VFD 1 249.00 249.00 https://buildyourcnc.com/item/spindl...-vfd-nospindle
Ball Screw Ballscrew, 200mm travel, 5mm lead, C7 Quality 3 118.35 355.05 automation products Control Resources: 16mm rolled screw, 5mm lead, 350mm overall, 200mm travel, 16mm diameter, 5mm lead, RM1605-0350-0200-FS
Ball Screw Fixed and Floating Endmounts 3 92.00 276.00 automation products Control Resources: Ballscrews & Accessories, Ballscrew end supports
Ball Screw Motor Coupling 3 16.00 48.00 http://www.controlresourcesinc.com/store/products.asp?cat=1396
Ball Screw 16mm Bracket 3 38.00 114.00 http://www.controlresourcesinc.com/store/products.asp?cat=1381
Ball Screw Motor Mounting Bracket 3 12.00 36.00 http://www.controlresourcesinc.com/s...s.asp?cat=1396
Linear Rail HIWIN Extra Wide, High Moment 2 53.78 107.56 http://www.controlresourcesinc.com/store/products.asp?cat=1388
Linear Rail HIWIN Miniture, 9mm Rail 4 34.59 138.36 http://www.controlresourcesinc.com/store/products.asp?cat=1069
Guideway Carriage WEH27CAZ0, Extra Wide Bearing Block 2 115.37 230.74 http://www.controlresourcesinc.com/store/products.asp?cat=1388
Guideway Carriage MGN09CZ0H, 9mm Bearing Block 8 30.00 240.00 http://www.controlresourcesinc.com/store/products.asp?cat=1069
Motors 320 oz-in, Low Inductance Steppers 1 539.00 539.00 http://www.cncrouterparts.com/3-axis...-kit-p-74.html
Sofware Mach3 1 175.00 175.00 http://www.machsupport.com/shop/mach3/
Water Cooling Water Pump 3 35.00 105.00 http://ugracnc.com/CNC-SPINDLES/Water-Pump-12V-79GPH-For-Water-Cooling-System.html
Water Cooling Heat Exchanger 3 37.50 112.50 http://ugracnc.com/CNC-SPINDLES/Heat-Exchanger-For-Water-Cooling-System.html
Water Cooling Vinyl Tube 15 0.75 11.25
Water Cooling Misc. Water Cooling Hardware 1 5.00 5.00
Misc E-stop button 1 14.95 14.95 https://buildyourcnc.com/item/electronicsAndMotors-electronic-component-e-stop-button-switch-safety
Misc 6 Limit Switches 1 30.00 30.00 https://buildyourcnc.com/Item/electronicsAndMotors-electronic-component-limit-switch-safety
Misc Electritian to Connect VFD's 1 200.00 200.00
Misc Cable Carriers 3 20.00 60.00
Misc Alumimun Plate 1 200.00 200.00
Misc Misc Hardware 1 50.00 50.00
Misc Shipping 1 50.00 50.00
Grand Total: $4,184.41


My Assumptions:


  • With my budget, a set of quality stepper motors would be more appropriate than a set low-end set of servos. These steppers will be able to accelerate a 5 pound gantry will ease.
  • HIWIN rails, grade C7 rolled ball screws, and a beefy aluminum structure would be adequate to reduce backlash/slop to less than 0.001”
  • An 800W Ugra CNC water cooled spindle will be able to run continuously for 8 hours, and be able to perform light milling and chamfering operations
  • A single 2.2 kW VFD will be able to run 3 800W spindles simultaneously at about 60% power for 8 hours at a time



Questions:

  • Am I crazy?
  • What should I be most concerned about?
  • Is my budget realistic? Am I missing anything?
    Will the final results produce smooth toolpaths, or sloppy, visible steps?


THANKS!