CNC Information and Projects

This first wooden table was based on the flying gantry system with an under-bed leadscrew.
This 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.

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. This is similar to commercially made bronze split leadnuts.
Tightening the bolt bent the rod coupler, and removed the play between the threads.

This turned out to be a 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.