Carving a Thinker - 1st attempt

I admit, that this was a moon shot. But I could not resist putting my new rotary module to a really demanding test. So I decided to take a nice piece of wood from a linden tree felled in our community a few years ago and to carve it into an abstract wooden statue of a thinker (original stl file acquired from Thingiverse)


The first task, obviously, was to get something smooth out of the raw basswood, i.e. to remove the bark.

The diameter of the branch was roughly 4.5 cm, I cut anapproximately cylindrical piece from it, some 17 cm long and placed it in the rotary module. As carving bit I used one that has a rather broad end of 8mm width, see the lower part of the next picture


Of course, setting the carving origin is rather tedious: One has to set the boundaries for the carving bit outside the perimeter of the irregular shape. Starting the process then requires patience, until after several rounds of carving plain air the bit bites wood.

The intermediate result was, so say the least, disappointing. While the wood of the linden tree is perfect for wood carving (soft, fine structure) - the bark is not. Right under the bark is a layer of very tough and stringy bast, which biologically serves to conduct fluids back and forth. Even a brand new milling bit was unable to cut through this stuff in a decent manner, rather it catches some of the strings and tears them off. Which reminded me that protective gloves and trousers for serious wood work with a chainsaw work exactly in this way: They contain fibers which are caught in the saw chain and block it rapidly.

Unfortunately, I do not have a video from this near failure. Footnote: My SnapMaker is connected to a Linux Machine, which is also connected to a WebCam placed inside the SnapMaker enclosure. The Linux Server runs OctoPrint (very nice frontend for controlling the printer), and OctoPrint has an internal features that allows to create time lapse videos - but so far only for 3D prints. For CNC carving and Laser cutting, Octoprint is still useless - but one may access the stream of the WebCam. TODO: Write a shell script that creates a time lapse video for CNC and Laser jobs on the SnapMaker

Fortunately, my wife came to the rescue. She took the damaged linden tree branch and put it into her lathe, taking away the bark and the bast layer within a few minutes. I ended up with a roughly cylindrical piece of basswood, 16 cm long and 38 mm wide. See below for an idea on how this looked. Note the shallow groove at the bottom: We will come back to this later in the post, for the moment we can forget about this, it was not present after the lathe process.

The next step then was to place this basswood cylinder into the rotary module, to set the origin properly etc. as prescribed.

Turning to Luban: The Blender model shown in the topmost picture of this post loads easily into Luban.

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I deliberately placed the lower end of the depth map a few millimeters away from the bottom, to leave some distance between the carving bit and the tailstock. Which of course would give me a kind of flat disc at the head of the statue, to be removed manually. Also, the 3-dimensional preview works nicely (I turned the picture upside down for better comparison)

Footnote: Luban could use a button to change the orientation of the display to “upside down”.

For the creation of the work path I had to set the final milling bit. I chose one similar to the one shown in the bit picture above: triangular shape, 0.5 mm flat tip, 15° angle. Path creation works ok - but to my surprise the “simulation” offered by Luban looks much less convincing


Also, the predicted carving time was 45 hours…

Well, I suggested to myself that the strange figure offered as simulation was an artifact, and that the machine could survive 45 hours of continuous operation. So I gave it a “GO” - at some time in the afternoon. The first 6 hours of carving went really good. Lots of carving dust had accumulated, so twice during this time I paused the process and took a vacuum cleaner to remove the dust. Watching the thing in the WebCam stream was a big plus: The first contours of the statue appeared - and were properly spared by the milling bit. Interestingly, the progress appeared to be much faster than predicted by Luban.

Around 23:00 I went to bed, at this time the progress bar on the display told me something of 26% completion - after 7 hours of milling.

Four hours later I gave in to a human necessity and took a detour to the basement to check the progress.
The completion was shown to be 57% (after 11 hours), but – oops:



I could watch that the milling bit went deeply into the wood, was redrawn, and the inserted into the wood in some different place - without cutting horizontally. The wood was simply no longer rotating when the bit was down (but the headstock was…).

What had happened?

Well, at some time in the previous 4 hours there was too much friction somewhere, and the clamps of the headstock turned slightly loose. The resistance created by the milling bit sunken in the wood was apparently bigger than the resistance created by the not-completely-tight headstock clamps. This led to the shallow groove at the unmilled end seen in one of the above pictures - while instead of cutting the bit was simply drilling.

Footnote: It may be that this loosening of the clamps occurs, when the milling bit is deeply in the material and offers too much resistance to the turning wood. Could this be prevented by inverting the rotation direction of the whole rotary module?

OK, so for the moment I am collecting the lectures learned from this. I will not give up, as I learned from Apollo 13: “Failure is not an option”.

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