CNC Milling Machine

This is a good description of CNC: http://en.wikipedia.org/wiki/Cnc

Milling machines have the ability to cut three-dimensional shapes from blocks of solid raw material.
When you attach a computer to an ordinary milling machine you get a Computer Numerically Controlled milling machine.
CNC milling machines are common tools used in the CAD/CAM process for prototyping, mold making, or Manufacturing.

This milling machine was designed and built for the purpose of keeping my hardware/software skills sharp.

Maximum Volume:	12in x 12in x 5in (Depth is limited by cutting bit length)
Minimum Resolution:	0.00015 inches (Depends on cutting bit size and flex)
Maximum Speed:	9.6 seconds/inch (Depends on material being cut)
Limit Sensors:	X,Y,Z Upper and Lower (With auto shutoff)
Platform:	GUI runs on both Linux and Windows
Protocol:	Standard 9-pin RS-232 serial port
Number of Axis:	3 - X,Y,Z (Some mills have more)

The body/platform of the mill is made with wood, screws, and glue.
The platform of the mill is driven by three high current high torque stepper motors. (One motor for each axis; x,y,z)

The low-level hardware driver is written in assembler, and run by an embedded micro-controller.
The high-level serial driver, point file interpreter, and business logic are written in C++ .

The Graphical User Interface was written using GTK and C++ .
The sample 3D range image was generated using a plug-in I wrote for Panorama.

1. Use your favorite CAD software to create a object, scene, or image.
2. Export/transform the object, scene, or image into a POINTS file. (Format of my own design)
3. Power up the CNC milling machine using the "ON" button.
4. Start the Main CNC Control window (shown below).
5. Click the "Adjust" button to adjust and zero the mill as needed.
6. Go back to the Main CNC Control window.
7. Select your POINTS file using the PointFilePath entry box.
8. Adjust the StepRate for the type and thickness of material.
9. Click the Start button and watch the machine work.

The Main Control window for the CNC system.

The window you get when you press Adjust on the Main Control window.

The mill cutting the word SUPER into a block of wood.

Close up view of the word SUPER cut into a block of wood.



The mill cutting a sample 3D range image into a block of foam.

The original scene used to generate the sample 3D range image.

The sample 3D range image.

Inverted verson of the sample 3D range image.

I have condensed all of the designs I've seen into these categories...

Rotating motion to linear motion:
  Belt (Timing belts; Found in most desktop printers)
    + Good for short distances.
    + Easy to find in old printers.
    - Hard to find long belts.
    - Can stretch over time or with excess force.
  Screw (Found in most hobby CNC machines)
    + Good for medium distances.
    + Easy to visualize.
    + Easy to find in hardware stores.
    - Hard to find long screws.
    - Adds inertia to spinning parts.
    - Alignment with the nut is critical.
  Rack
    + Good for long distances.
    + Can easily make longer by adding more lengths.
    - Hard to find in local parts stores.
    - Alignment with the gear is critical.

Reducing friction and guiding the position:
  Slide (No Bearings; One material slides on another.)
    + Easy to find low-cost parts.
    - Larger motors to overcome friction.
  Inside Track (Bearings ride on inside of shaped channel.)
    + Great for custom and small designs.
    - Difficult to find or build matching tracks and "shuttles".
  Outside Track (Bearings ride on outside of round or square tube.)
    + Easy to find low-cost parts.
    - Requires more than one tube/track for stability.
    * Square tubes are generally more stable than round tubes.
    * Round tubes generally require less bearings.

Servo vs. Stepper Motors:
  Stepper
    + Low cost H-bridge type driver.
    - Higher cost for higher torque.
    * Typically no feedback sensors required.
    * Typically no real-time controller required.
  Servo
    + Faster response times.
    + Lower cost for higher torque.
    - Requires feedback sensor.
    - Requires real-time controller.



I would build a small sized machine with:
  Screws or Belts.
  Stepper motors.
  Slides.

I would build a medium sized machine with:
  Screws or Racks.
  Servo or Stepper motors.
  Outside Tracks (Square).

I would build a large sized machine with:
  Racks.
  Servo motors.
  Outside Tracks (Square).

Note: Wider and more contact points == More stable/accurate movement.
Note: Less mass/weight == Less required motor torque.
Note: Less friction == Less required motor torque.
Note: Try to move the cutter not the work.

Search www.google.com for "CNC milling machines"