Luban 4th axis milling is cool! And dumb... And dangerous!

TL;DR: Neither Luban nor Snapmaker take the available bit length into account, so that you can run your toolhead (the collet to be more precise) into your workpiece. Also: The Linkage-Algorithm has bugs that let the bit run into wrong places of the workpiece.

Long story:

I received my Rotary Module on Friday, and have since then trying to mill this:

I know, I know, does not look like a beginner project… Still, I was curious if I could coax it from the machine, a friend of mine asking me to 3D-print this, and I thought: How surprised would he be to get it in wood. Or Epoxy tooling material.

So starting off with wood, I followed @Skreelink’s Multi-Pass Rotary Guide (Thanks again for that one!) and created a roughing pass for a 4mm flat end mill, and a finishing pass for the Snapmaker Groove V-bit that comes with the module. Both needed to be of type “Linkage” (XYZA), since there are parts that are not accessible to the milling bit in “Rotation” mode (XZA).

I am truely impressed that Snapmaker’s Luban offers a true XYZA (or more YXZB with SM2) toolpath generator! Kudos! I have by now looked into the feature sets of many CAM products that cost several 1000 bucks, and not many offer that. And I guess that’s far from trivial to code! So thanks for that to Snapmaker!

That said (and not wanting to diminish that): There are issues.

The first: No true multi pass milling. With the tricks shown in above mentioned guide you can achieve a roughing and a finishing pass, but with little control. Still, looking at where Luban already is, I’d assume that doing proper rest material machining should not be too complicated! Snapmaker, it would be great if that would come around the corner soon!

The second: The diameter of the milling bit is not correctly taken into account. I have many places where I could see that, but I guess it is best explained when I show my support structure - I decided to add a cylinder and a cap so that I could have the tailstock always attached. The cylinder going down to the head of the dwarf is 5 mm in diameter:

I specified the roughing pass with 2 mm allowance, so the cylinder after roughing should have 9 mm in diameter. What came out was an oval shaped thing of 7-8 mm diameter. The sword, which should have been 4mm plus the sword’s thickness, is 2.5 mm after roughing. Here’s how it actually looked after roughing:

Honestly, I doubted that I’d get the dwarf out in the end, but I started the finishing pass with the Groove V-bit. That showed:

The third issue: The bit ran into the workpiece! It happened in the mid of the 5 mm support cylinder, and by chance I was standing beside it and watching. The toolpath just rammed the bit into the support cylinder part of the workpiece, until it broke. Job failed… Seems that the anti-collision algorithms need improvement…

Here’s the sad result:

I can still stick the parts together and you can see where the V-bit gnawed into the wood:

Btw.: The 5 mm cylinder after the finishing (with 0 allowance) was done, resulted again in an oval shaped thing of 4-5 mm diameter.

OK, I thought: Wood/two pass milling is too advanced right now (doing all in one run in wood with the Groove V-bit would have taken 20 days(!) with default settings…), so lets use the Epoxy tooling material cylinder that comes with the module as teaser. This is relatively soft, and the Groove V-bit can cut right in to its full depth, so doing the dwarf in singe-pass, 0-allowance linkage toolpath, is estimated to take 5 hrs or so. But right the second cut showed:

Issue number four: The collet ran into the workpiece (I’m sooo glad I purchased the Stop-Button!). Luban never even asks for your bit length, but Snapmaker touchscreen does. Nevertheless, no safety measure stops the toolhead:

So, I’m still a dwarf short (pun intended :slight_smile: ), suppose I’ll revert to 3D printing for the time being. I’ll try later with a longer V-bit and the Epoxy material, but I first have to find a suitable bit. Since I’m off for a journey soon, this may take some time.

Aside from these bugs and shortcomings, I was pleased by the assistance the machine gives me: Origin assistant and bit assistant are well made and make a lot of sense! Good job here!

@Jade, @Riskey and the rest of the Snapmaker team: Again Kudos for having the “Linkage” toolpathes - please debug them, add the bit length into the calculation, improve collision avoidance, and make it multi-pass - then Luban will be an extremely valuable tool!!!

I am very much looking forward into my next adventures of 3D milling!


Hi all,
I sent in a support ticket on this case, and Snapmaker confirms that there are some imperfections in the current algorithm:

Currently, linkage machining does not consider the shape of the tool. Considering the shape of the tool is a very difficult task. Currently, it is recommended to use rotation and set a relatively large margin. If it is a flat-bottomed milling cutter, it should be larger than the tool radius

I am looking forward to the point where Snapmaker will improve their algorithm - it would be a real game changer if they’d offer their linkage with correct result! Even expensive commercial software is often not offering proper XYZA machining. Go, Snapmaker, Go! :slight_smile: And thanks to Support for looking into this.


OK I promised pictures - before I do a full writeup of my odyssey to get there (too late today), here at least a few pictures of what I would call a success (not perfect, far from what a resin printer could do with ease, but nice enough!) with an 0.2 mm nozzle and PVA as support interface material:

Print finished:

Meet Rendor Holoam, the Prince of the Silver Dwarfs:

The pictures, showing every shadow in harsh light, look worse than the original - it turned out really nice IMHO!

EDIT: Full writeup here: Tabletop miniature with 0.2 mm nozzle and PVA support (Dual Extruder)

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