Circle Diamond Square

There is a test you can run to check the accuracy of your CNC mill. It’s called the “Circle Diamond Square” test. It’s real name is “NAS 979; Composite cutting test”

Essentially you mill a circle, in a diamond, in a square. The real test also has some other features such as a 5° ramp and possibly a few more. It’s hard to find the real test on the internet.

I made up a circle diamond square test for my mill and ran it today.

I also made a mount for a drill press vise that I had. I bolted it to a piece of 3/4″ MDF and then used the holes in the table to bolt it down.

If you’ve been following along, you might also notice that I added another 3/4″ riser under the ends of the machine to get more height under the spindle. I might go another 3/4″ still.


Here is a close up of the finished part.

Circle Diamond Square
Circle Diamond Square

It sure looks nice. Then I measured it.

This is a drawing of what the dimensions are supposed to be.


Here are the actual measured dimensions.

Actual part.
Actual part.

It’s kind of messy, but essentially it appears that I have a backlash problem somewhere. The big square is good, the diamond is okay in one direction, and large in the other, and the circle is an egg. I’m not sure exactly what the issue is, nor how to fix it.

It’s pretty good for a DIY CNC machine, but I’d like to get it a little better. I’m going to see about making sure all the wheels are adjusted the same and the belts are nice and tight. There is some inherent backlash in the belts and pulleys, but I don’t think it’s that large.

I’m having trouble locating the real test information so that I can interpret my results, but I’ll keep searching.

Oh, and the more I use CamBam, the more I like it. It just works the way I expect it to.

Running total costs.

All Shapeoko CNC Mill Posts.

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