Testing the Limits: Surface Finish Analysis of Pocket NC Machines

We often get asked what surface finish the Pocket NC machines can achieve. And while we have known, and seen, that the machine can produce a near-mirror surface finish, we have never taken the time to put an official number to it. 

With the addition of a few new team members, we finally had the ability to put some time into finding this value, so that is what I set out to do.

Scale showing surface roughness of 0.4 to 12.5 um Ra for horizontal milling, vertical milling and turning.  Images are machined metal with roughness marks.

Surface Roughness Scale

I figured doing these tests in metal would be the most applicable and give me the clearest results, so I snagged a piece of brass we had laying around and got it loaded in the machine.

1” brass stock held in the ER40 Collet Fixture

The Datron tooling we carry has proven to create a nice surface finish on other projects, so I used a 4mm single flute endmill for this test as well.

Tool used for testing Datron Part 0068434Y.

To keep the testing simple and quick, I threw together a quick model of a cube. This allowed me to create two different types of toolpaths - one where I was cutting with the end of the tool and one where I was cutting with the side of the tool. And with the four sides, I was able to try two different speed and feed recipes each time.

Screenshot of toolpaths for machining a square side on to a cylinder.

Toolpaths for cutting with the end of the tool

Similar toolpaths for the top of the part.

Toolpaths for cutting with the side of the tool

Since we have seen nice results in the past, I started by using my go-to speed and feed recipe on both cutting orientations.

Photo of the toolpaths shown in previous screenshots.  The materials being cut on the desktop CNC is brass.

Cutting with the end of the tool

The results were really nice looking for both orientations so I brought our surface finish scale to the part and started comparing the newly cut surfaces to the various swatches on the scale.

closer image of the resulting surface finish

First set of results

Image of the surface roughness scale to compare to the brass.

Using the roughness scale to determine Ra value

After repeating this process a few more times with slight tweaks to the speed and feed recipe, I took the best looking surfaces back to the surface finish scale and compared.

Second round of cutting with new speeds and feeds

In the end, the best surface finish I achieved with this combination of tool, setup and material was about 0.6 micron Ra, while cutting with both the end of the tool and the side of the tool.

completed test cut on brass next to 0.4um Ra on the scale

Best looking cut compared to the roughness scale

This was a simple test but it gave us some great results that we are excited to share with existing and future users. I hope you enjoyed coming along for the ride! 

Until next time, Happy Machining!

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Pocket NC 101: 5-Axis CNC Machining in the Classroom

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Incorporating the Pocket NC into your shop to keep the big machines making $$$