Super Gerbil CNC Controller Accuracy Testing

A simple acrylic disc for machining accuracy check

We machined this simple acrylic disc to give us confidence that Super Gerbil was working accurately.

It’s time to test the Super Gerbil CNC controller accuracy, so we designed some simple shapes in Fusion 360 and machined from some clear 4.4mm acrylic. First up, a disc with a design diameter of 25.00 mm in Fusion 360:

Measuring the sample circle
Dimensions of Sample Circle

After the machining was complete, we broke out the measurement gear, including a nice old micrometer from my grandfather and my go-to daily verniers.

Scale shows 0.985" - 25.019mm
Grandfather’s micrometer coming in handy for measuring our test disc
Checking the disc accuracy
0.0985 inches translates to 25.019mm
Disc size was 25.00mm by design
As an alternative to the micrometer, we also measured with verniers, got the same answer

Both measuring devices came up with 25.02mm diameter, so that’s 20 micron error against our design diameter of 25.00mm.

Next step was to design a matching pocket for the disc. I used a diameter of 25.08mm, based on my experience on the right increment for a sliding fit. I was pleasently surprised – the disc easily slides in, and is in fact at the point of slipping out. I put this down to the smooth and uniform machining effectively reducing the fit, as described on https://en.wikipedia.org/wiki/Engineering_fit.

Of course I have to acknowledge that these good results are a result of many systems working together well: Fusion 360, the UGS G-Code Sender, the Super Gerbil, and of course the excellent mechanical design of the Nomad 883 and a new endmill. The point of the test was to show the Super Gerbil controller didn’t let the other components down.

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