Concrete CNC Router

I started designing a CNC router. The bed and beam are supposed to be cast from UHPC (Ultra High Performance Concrete). This is a very dry concrete mix with aggregates that increase its mechanical strength and a plasticiser that makes it viscose enough to be usable for casting again. The end product can achieve mechanical properties comparable to aluminium and has very good vibration dampening properties.

If you’re interested in some of the basic things to consider when designing with concrete, check out this great series on the topic by the “Practical Engineering” channel on youtube.

The design uses 20 mm linear rails all 600 mm long. Ball screws on X and Y are 16 mm SFU and 12 mm SFU on Z. All bearing blocks are standard BK/BF style. Motor flanges are NEMA23. Drawn are JMC iHSV57 servos. The design would also allow to use steppers geared down with pulleys.

Design Notes

The main idea behind the bowl shape is to create a partially enclosed volume that allows to use flood coolant without creating a mess. It also raises the y-rails to an optimal height.

All bearing surfaces are metal pads that are glued into the finished casting and anchored with pins. This allows to achieve high position and alignment accuracy without the need for a large mill. If a mill would be available, milling the bearing surfaces after the glue-up would be ideal.

The port holes in the side are mounts for an optional 4th axis to enable mill turning. They also allow to attach dust extraction when milling wood and double as an all purpose bulkhead.

Two threaded rods put the beam under compression along the x-axis to increase its strength.

Molds

Open Source Brushless Servo

The odrive is a open source high performance brushless servo platform based on RC BLDC motors. Great Stuff!

Key Specs

  • Two motor channels.
  • 24V, designed for more than 100A peak current.
    • 48V version just released.
  • DC-DC converter, for brake resistor or energy storage.
  • Encoder feedback for arbitrarily precise movements.
  • Supports power regeneration.
  • Optional use of a high power density battery means you can achieve >1kW peak power output with only a modest power supply.
  • Open source: HardwareSoftware

Interfaces

  • USB Serial port — PC, BeagleBone, RaspberryPi, etc.
  • CAN — CANOpen and CiA 402 is a possibility.
  • UART — Arduino, mBed, etc.
  • PWM — RC Recievers, Arduino, etc.
  • Step/direction — Existing motion controllers
  • Some general purpose digital and analogue pins

Protocols

  • Many types of command modes
    • Goto (position control with trajectory planning)
    • Position commands
    • Velocity command
    • Torque command