CNC Test Program Prepares For Fixtures

My test program exposed an electrical noise issue and helped us track it down to the spindle motor. This was an unplanned but very welcome bonus result on top of its original purpose. It was my first foray into Autodesk Fusion 360 CAM module after following tutorials. I wanted a simple program with few operations, small enough for me to fully understand the G-code output from Fusion 360 post-processor for Grbl. We had scrap pieces of MDF on hand for practice cuts so it wasn’t important for the test program to do anything useful. But as I was contemplating work holding for scrap MDF, I realized my first program could be useful after all.

The work surface we installed earlier was also laminated MDF, cut from the same retired treadmill board as the test scraps. Its smooth (well, scratched up, but still relatively flat) top surface is not conducive to any kind of work holding. The original plan was to cut holes by hand with a cordless drill and fasten work pieces using bolts from above fastened by nuts from below the sheet.

Then we had a better idea – use threaded inserts. Counterpart to the heat-set inserts I’ve been using in my 3D printed plastic(*) projects like Sawppy, there are inserts available for wood.  They have a self-tapping coarse thread appropriate for wood on the outside, and a durable machine thread on the inside. Given that our XY table used mostly 1/4″-20 thread, we will continue the trend by using these inserts from McMaster-Carr.

All we needed to put these in was to drill a hole of the specified diameter, and this is a task I can have the machine do for its own work table. I first started with a single hole, walking through each line in the generated G-code to understand what’s going on. The results were fine for the insert itself, but the exterior thread damaged surrounding laminate surface during installation.

Inserts with cracked laminate

This lead to extension of the test program, adding a second cutting operation. The first one cut a hole all the way through the surface for the insert, and a second shallower cut to clear surrounding laminate to avoid damage by exterior tread. Once the metal insert was installed with help of an alignment tool, we have a clean fastening point to bolt work pieces to our machine work surface.


(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.

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