Learning to mill: Random chinese dragon bas relief

Hi folks,
coming from 3D printing, I had a lot to learn for CNC milling! So I picked some piece of leftover wood from my cellar (douglas fir actually) and decided to create a bas relief from it. Understanding that Luban can do this “out of the box” from a grayscale encoded height-map image I thought this would be an easy project - turns out it’s not :slight_smile: Hope my short description here helps others!

I picked this dragon more or less randomly from the Google picture search. Grayscale encoding means: The whiter, the higher. If you put this into Luban, you can generate a relief toolpath. However, as soon as you change settings, at least for me the program either crashed or just said “Cannot generate toolpath”. Also, multiple passes were just not possible.

So I switched to Fusion 360 and guess I condemned my self to hell by the amout of bad curses it uttered while trying to figure things out on myself. Fusion 360 is the exact opposite for me to what I would call “intuitive GUI software”. I don’t mean the desgining of things - it’s clear that learning is involved here. I mean simple things like: Mouse scroll wheel works exactly opposite as compared to every other application on the globe! Clicking on an Object sometimes locks operations for no obvious reasons. In order to edit a mesh you first need to activate a feature in some deeply buried option dialogs… OMG! Still, with the help of these resources I finally get things ready:

  • Videos by Lars Christensen - extremely helpful!
  • Tutorial on getting a grayscale image as relief into Fusion 360
  • Tutorial on creating a bas relief in Fusion 360 with Snapmaker 2 - you need to replace the part where this guy loads an STL relief by the tutorial before.

Still, none of the above does multi pass. But it is not that difficult. I did the following:

  • First, do adaptive clearing like in the tutorial with the largest flat end mill at hand (I only had the Snapmaker bits, i.e. a 3.175 mm 2 flute flat end mill was the largest)
  • Then right-click on the result in the operation tree and choose “Create derived operation” and pick another adaptive clearing. The result is a new operation that has basically the same parameters than the one before. Now pick a ball end mill. I only had the Snapmaker 3.175 mm ball end mill, and this already gave awsome results, only that smaller details could not be carved since the mill was that big. If you have, pick a small one. Maybe you’re already done then. Important: In this (and any potentially following tool paths) in the Geometry tab select Rest machining and choose “From previous operations”. This makes sure you are only milling in remaining material and not in thin air.
  • I had a 1.5 mm single flute flat end mill, also Snapmaker brand. With this I did a scallop, and two parallel passes in X and in Y. This worked out the details, but left many artifacts. I guess with a ball end mill it would have looked much nicer! I stopped here - It was for learning, not for carving the perfect dragon. If I wanted that, I first would need to shop for more bits.
  • From each toolpath generate the CNC file via post process (like in the tutorial)
  • Send it to Snapmaker one after the other and change tools inbetween. Make sure to note down your X and Y work origin! Snapmaker forgets it on power down! Z origin needs to be re-set for each tool anyhow. If you look closely you’ll find that the touchscreen allows you to set Z origin individually - you need to swipe for that. All tutorials suggest to set the work origin in the center of the workpiece - I would not do in the future. The center of the workpiece will most likely get milled away, so better choose a part that stays for relibale Z origin setting for each tool.

And here is what it looks like…

…after the first roughing pass with the flat end mill

…after the second pass with the ball end mill - I like that one already very much:

… after the 1.5 mm flat end scallop and one parallel pass, already much more detail - if you zoom in you can see artifacts/imperfections from the flat end mill:

…and the point where I stopped since I had no better bits available. I find this already remarkable and it shows where you can get if you have the right tools!

Some take-aways:

  • Have the right bits
  • Set the work origin not to a place that gets milled away
  • note down your work origin to have it after a power cycle
  • Don’t use a ball end mill for the roughing pass - it’s the wrong tool for it and I could see how much load it put on the Snapmaker toolhead! It was visibly lifting on tree rings, and douglas fir is not even hard wood!
  • Fusion 360 and me will never fall in love I suppose… I think I’ll try out other software at some point… Still, I can see how powerful Fusion 360 is! It’s UI is just so… strange! And cloud, cloud, cloud… don’t like it…
  • Snapmaker is a cool thing!
  • For serious wood work the stronger spindle announced will be very welcome!
  • Dust goes everywhere!

Has been fun!

Hauke

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Very nice, excellent work. I’ll be watching the videos and using your tips, thanks!

Good info. Thanks. I’m looking forward to doing some CNC on my machine.

Great article - thanks. I only have the Snapmaker original and have struggled to do any decent cnc. You have inspired me to give it another try. Funnily enough one of my first efforts was a dragon too. I agree with your observations particularly about the beast that is Fusion 360 - amazing program but a real beast. I hope it is easy to purchase add cutters to the library to be able to improve detail. Unfortunately my email to Snapmaker support re problems and issues with cnc has had no reply - yes, I am sure they are busy but even an automated reply saying “Please be patient, we will get back to you soon” would be appreciated.

Thank you so much for this. I’ve been scratching my head trying to understand the process for cnc having never done anything like that before, and fusion 360 is a nightmare! Just having a basic work flow to learn from is brilliant.