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Kiri:Moto Quickstart

To turn a part in CAD to instructions for the CNC, you need a CAM software (in 3D printing terms, it's like a slicer for your CNC). Some CAD software comes with this built-in already, like Fusion 360 or FreeCAD. Onshape has one too, but it's paywalled for now. There's also standalone CAM software: the Shark HD4 came with a VCarve Pro license.

The one we've been using, though, is the browser-based Kiri:Moto.

Why Kiri:Moto?

Kiri:Moto is not very commonly used. It's fairly small and the official documentation is not the best. However, it's FOSS and runs in the browser! It's unblocked on the Chromebooks, which means you won't need to bring a separate computer just to program the CNC.

Getting Started

First, you'll want the workspace files. These contain a snapshot of all the settings in Kiri:Moto, including the CNC machine's parameters.

Base workspace

Above is a quick example of creating the gcode for a drivetrain plate.

Explanation:

  1. Switch to CNC mode (the default is FDM for 3D printing)
  2. Import the starter workspace to configure the machine and tools, if you haven't previously
  3. Import the model you want to cut
  4. Reorient the model
  5. Add tabs - the machine will avoid these, leaving something to keep everything together while cutting
  6. Configure drill operation, which marks the holes
  7. Configure trace follow operation, which cuts out the inner voids
  8. Verify everything looks correct with the slice, preview, and animate tabs (optional but recommended)
  9. Export gcode

More Stuff

Drilling holes and the "fake end" tool

As mentioned in the Bits section, endmills can't really drill holes the "normal" way. A solution you'll find online is to use a helical operation to gradually ramp down the hole. However, our holes are too small for helical to work well! M4 holes only around a millimeter wider than the endmill. The endmill makes very tiny circles when going down, and tiny circles are very, very slow...

To avoid having to wait almost 10 seconds for a single hole, we mark them instead by plunging with the endmill a short distance. This gives us a reference to drill out the hole afterwards with a proper drill bit and the drill press/hand drill.

We can accomplish this with the drill operation, but the "Select Matching Diameter" button won't autoselect a hole unless the bit has the same diameter as the hole. Hence, the "fake end" tool: this is identical to "end 1/8," but with a 4.3 mm diameter, the same as the model's holes. Adjust its diameter through Setup > Tools to match your model's holes. You could also select the holes manually with the normal "end 1/8" tool, but that gets annoying fast.

Z bottom

The global z bottom setting in the left sidebar sets how far below the part the machine will cut. It should be set a little below 0 to ensure the part gets fully cut out. The machine will sometimes cut slightly into the wasteboard with this set below 0, but it's better to cut too much than too little.

Tabs

Tabs aren't as important nowadays with superglue workholding. I've never tested cutting without them completely, but it wouldn't be impossible. Put them near thin areas to reduce vibration and fluttering!

Feed and plunge rate

Feed rate refers to how fast the router moves horizontally, and plunge rate vertically. There are recommendations and explanations you can find online for deciding feed and plunge rate, and the current settings should be roughly in those bounds. (I think the current settings are for ~20k RPM?) Note that there's both a global feed/plunge rate and a feed/plunge rate for individual tools.