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4th Axis CNC Fixtures

April 29, 2021 1 min read

4th Axis CNC Fixtures

A three axis CNC has become a pretty affordable tool for even a hobbiests.  However, the step up to a 4th axis can be daunting and expensive.  Luckily, with the use of a 3D printer, one can get most of the capabilities of a 4th axis on simple three axis router table. 

In this project, Common Fibers needed to machine precise holes, slots, and squares around the diameter of a carbon fiber tube. With the use of some simple 3D printed fixtures, we were able to achieve a high tolerance product within two days.  

The basis of the design is simple:

  1. Create mounting blocks that secure to the CNC table and fixture the tube in place in the X and Y directions.  
  2. Design a block with rotational fixture points at all angles that need to be cut.  
  3. Make some brackets to hold the tube and fixtures in place, locking in the Z axis. 

In this case, we needed to be able to machine the tube every 45 degrees, so we designed an octagon fixture block.  This block was bolted around the tube and placed into the mounting blocks.  Each operation was then run as a simple three axis setup and then rotated 45 degrees before the next was run.  The results are repeatable and don't require an expensive fourth axis or as complex of G-coding. 

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