Troubleshooting

CNC jobs can be difficult to set up correctly and some errors may not be identified by the technician. To ensure the best outcome for your job, please refer to this Tips & Errors.

2-Axis Tips & Errors

Ensure Lines/Curves are Planar

Check that your geometry is at the top plane of the stock and that no points are below by examining the left, right and front view ports. Refer above to correct example of selected geometry in yellow. Use command SETPT > Z Axis

Join/Close Lines and Delete Duplicates

Duplicate lines may cause confusion to the Fab Lab and must be deleted. The command SELDUP will remove most duplicates but you must also conduct a manual check. Overlapping lines may be simplified by the command MAKE2D. Join together lines using command JOIN. Lines that are used to specify different operations must not be joined.

Close geometry that is to be Profiled, Pocketed or a Containment Region.

Allow at Least 30mm Between Objects

Unlike the lasers, nesting of objects is best done by allowing for a profile of each individual object of at least 30mm.

Please do not attempt to share edges for small objects.

The Fab Lab will advise you during your consultation as to the best nesting practice for your geometry.

Don't Group Objects

The best way to control your geometry is by the use of the layers provided or the creation of additional layers using the proforma. The grouping of objects is not suggested as the Fab Lab may be required to alter the nesting of your geometry.

Limitations

Bits are cylindrical in shape and work by high speed rotation. In plan, a bit is best represented by a circle.

Unlike a laser, which has a beam width of less than 0.5 mm, a CNC bit is usually 6.35mm or larger. If you conceptualise a circle moving in plan you will have a good idea as to the routers limitations.

This means that sharp internal corners are impossible to achieve without post processing or other machining methods.

3-Axis Tips & Errors

Clean Geometry

Clean single polysurface site model

Where possible, keep geometry represented by the most basic shape possible. Highly complex, intersecting or flawed geometry is often unable to be ‘read’ by the toolpathing software.

Use Boolean Union

Use the command BOOLEANUNION to connect your geometry together

Before Boolean Union

After Boolean Union

Minimize Intersection Geometry

Some intersecting solids are acceptable, but the more you have the longer the toolpathing time and cost.

Boolean Difference

Boolean Difference is a quick way to subtract from a geometry and maintain the negative. This is usually used when creating the footing for 3D Printed buildings for a CNC'd base model.

3 Axis CNC Limitations

3 Axis surface milling effect on styrodur surface

The CNC Router operates in 3 Axis which means that it can simultaneously move in the X, Y and Z axis.

3 Axis movement is best understood as a projection from the top view port; geometry unable to be ‘seen’ from this view will not be able to be milled.

General CNC Knowledge

Rounded Corners

Concave corners, or corners less than 90 degrees, will not be able to be milled to a sharp point due to the diameter of the router bit.

Rounded Corners - Joints

dogbone example on finger joint

When milling finger joints it is common to use another process to clear away the material left in the concave corners. Allowing the parts to fit precisely together. ‘Mickey Mouse’ and ‘Dogbone’ cornering are two methods that clear this material away.

For more indepth information look at Dogboning Sharp Corners.

No Hidden Pockets

Geometry or spaces below a surface will not be able to be read or routed.

No Undercutting

Areas that lie beneath an overhang will not be able to be routed normally. It is possible to flip the material over and mill the bottom side. This usually requires the use of a jig and should only be undertaken after consultation with Fab Lab staff.

Bit Length

The tool housing may clash when attempting to mill deeper than the bit length. The Fab Lab is able to identify these clashes with simulation software prior to routing. In some cases this may result in the inability to complete a job.