CNC Information and Projects

This first wooden table was based on the flying gantry system. It was an experiment with CNC, so it was built as inexpensively as possible with shop scraps.

The machine was made primarily of sheathing plywood.
The rails were black iron gas pipe, and the bearings were 608 skate bearings.
The leadscrews were threaded rods, and the leadnuts were rod couplers.

The machine used 420 oz.in. servos that were driven by Gecko 320s. These were recycled into a larger metal machine.

This type of machine has many limitations, which are listed at the bottom of this page.

Bearings bolted to angles were used for the Z axis.

The bearings were attached to the Z plate, and the rails were fixed to the carriage.

This system was difficult to align and tension.

It became clear that for the shorter Z axis, it is better for the rails to move, and for the bearings to be fixed.

Stiff rails would add rigidity to the moving components, and the bearings could be tightly tensioned.

A leadnut was a rod coupler, which was cut almost all of the way through. Tines were welded onto each side of the cut.
A bolt was threaded into one of the tines; it free-wheeled in the other.
Tightening the bolt bent the rod coupler, and removed the play between the threads.

It was clunky, but it seemed to work. However, this turned out to be a complete waste of time.
A rod coupler by itself can give backlash in the 0.003 inch range, and any adjusting of the system in the picture just added drag.

This plastic sign was made with a 0.03 inch bit chucked in a Dremel.
The quality of the cuts was better than expected considering the quality of the table.

However, heavier work was of low quality since everything could flex.

The second image shows two problems.
One is the wavy lines permitted by the machine's flex.
The other is a software problem that sometimes occurred with different DXF files. The extra lines were visible in some programs and not others. The joys of cobbling software.

Building this machine showed that this popular design is inherently flawed for a number of reasons.

• Unsupported rails are flexible and permit chatter.
• The tall gantry ends allow the gantry to rock on the rails.
• The ends of the gantry prevent wide stock from being milled.
• The center leadscrew does not support the ends of the gantry, so the gantry racks under low cutting forces.
• The under table leadscrew is in the way of bed supports, so the machine cannot carry heavy stock.
• The space under the machine is lost to other uses including fourth axis components and storage.