Posted by SainSmart on November 16, 2022

Written by Anastasia. You can find me on the Facebook group SainSmart Genmitsu CNC Users Group All comments, suggestions and corrections are welcome.

This is a guide on how to make the star version of my Festive Harmony ornament on the 3020-Pro Max (27% OFF, Only $439! Black Friday Dust Shoe & Chromatic Milling Bits Bundle Sale). It is a dodecahedron with Christmas-themed sides, which are held together by a wireframe spherical icosahedron.

It was originally designed for 3D printing (and can be found here: https://www.thingiverse.com/thing:5152271), but ever since I got the 3020 Pro Max, I knew I had to make a CNC version, so here it is! To make your own using the designs provided, you will need:

- 4 mm plywood sheets

I used 250 mm x 200 mm sheets, as they allow making multiple instances of the dodecahedron side and the connector while still being securely held on all four sides by the clamps that came with the machine.

- A 3.175 mm downcut bit

I used the 8mm bit from the Sain Smart SD06A bit collection. A downcut bit ensures a clean cut on the top surface, but typically leaves some strands on the bottom one; however, these can easily be trimmed with a diamond needle file.

- Sandpaper and diamond needle files for cleaning up the carved pieces

- Varnish / oil / paint depending on your preferred finishing method

I used Fusion 360 for toolpath and Gcode generation. All tool paths are 2D contours with the following parameters :

- Spindle speed: 10000 rpm

- Ramp spindle speed: 8000 rpm

- Cutting feed rate: 1000 mm/min

- Ramp feed rate: 500 mm/min

- Plunge feed rate: 300 mm/min

I used a ramping path with a 2 deg ramping angle and a maximum ramp stepdown of 1 mm. If your software does not support ramps, you could cut the profiles at multiple depths, using a maximum depth of 1 mm.

Before carving the actual components, we will need to decide how to carve the internal corners and find the machine tolerance.

Since bits are round, the internal corners will not be sharp; to alleviate this, we could redo the contour with a smaller diameter bit, or have the bit path extend outside the contour (dogbone). Note that depending on how the path is extended, the dogbone might be visible when the parts are assembled.

I did not have any small diameter bits, so I went with the dogbone option. I installed the Dogbone add-in for Fusion 360 and added minimal dogbones on all internal corners. You can download it here:

https://github.com/DVE2000/Dogbone

After choosing an internal corner machining strategy, we will need to apply it to the test-fit_star.dxf and test-fit_connector.dxf designs and carve them using varying offsets to determine the optimal tolerance. I recommend insetting the contour by 0.1 mm at first. If you plan to paint your ornament afterward, you might need to take this into account as well - I used a 0.05 inset that resulted in a very tight fit. In Fusion 360 the relevant option is ‘stock to leave - radial’.

Now we are ready to make our ornament!

We will need 12 stars and 30 connectors. Fit as many component instances as you can in your plywood sheet, add tabs, and let your robot work its magic. I was able to fit 4 stars per sheet and 14 connectors per sheet.

When the pieces are ready, carefully remove the tabs. Tabs around 1.5 mm high can be broken off by hand, but it might be better to use a small hand saw to reduce the chance of splintering. The strands at the bottom surface and tab residues are easily removed with diamond needle files.

There are various options for finishing the parts. You could simply use oil or varnish, particularly if you made the stars and connectors out of different kinds of plywood; or you could paint them. I went with the second option and used a glittery paint mixture for an extra festive look. I mixed a glass paint containing a suspension of glitter particles with epoxy paints in solid colors and applied two coatings.