A first venture into the world of DIY CNC.

Part 1 Basic Gantry Design

This project aims to build a CNC machine with nothing more than what is found in a common hardware, timber and electronic store.  The main aim of this design is to explore the possibilities of building a machine where each plane is set by only 1 surface. This would allow the  machine to be built without needing special alignment tools while minimizing backlash.

The guide rails are made from steel rectangular tubing. Each rail is acted on from both sides by skateboard bearings. Two bearings locate the position of next axis, while a spring loaded bearing on the other side of the guide ensures that the machine is pressed up against the guide surface.

The most common gantry configuration

common gantry type

A map of the machine parts

zaxis The Z Axis
yaxis The Y Axis
xaxis The X Axis
leadscrew Lead screw
guide image Rectangular guide
Circular guide

OpenD CNC Mark1

mark1 cnc

Unlike most gantry type CNC machines, this unit has a wide rather than high gantry so a to keep the twisting forces as close to the rails as possible. This should reduce the amount of play the machine experiences.

The guides

OpendCNC mark1 uses rectangular tubes and (608) skateboard bearings as opposed to circular tubes and linear bearings. Also, 3 rectangular tubes are used in each plane. for the X and Y axis, this means the vertical load is experienced only on the 4 guides highlighted below.

vertical load

On the X and Y, the sideways forces are handled by one guide per axis (the light gray ones). Two X axis lead screws are used as a single lead screw would potentially place tremendous twisting forces on the x axis guide (light gray).

close up

Here is a close up of the Y and Z axes. The MDF sections (in red/brown) are placed so that the forces experienced are always along the sides rather than the thickness of the board. This increases the designs stiffness.

The Z axis carries the guides with it, as this allows the bottom bearings, mounted on the Y section, to be as close to the work face as possible, once again increasing stiffness.

CAD software

The CAD software used to model the machine is Blender and a good tutorial on how to use it as a CAD package is available from rab3d.

Forward to part 2...

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