Grbl development log RSS

Grbl is a free, open source embedded CNC controller for the AVR series of microcontrollers. The initial version is still under development. The source code and an overview of the current status can be found at the github repository. These are my development notes.

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Jun
18th
Fri
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Move on

Nothing to see here. Move on to the Grbl documentation pages, our follow development announcements on twitter or read our nascent lab blog.

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Feb
15th
Sun
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First complete job … completed

I finished a little Air-app to stream complete jobs to the Grbl and render the result. This is the first “full scale test” running some 7000 lines of sample G-code I scrounged from this thread on CncForum. The Air-app feeds g-code to the microcontroller one line at a time, while the microcontroller generates the steps and feeds them back to be simulated in the Air-app. Everything seems to be working perfectly - the only thing missing now is a test with real steppers on a real machine.

You can get the code for the Air-based test-harness at the github-repository

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Feb
14th
Sat
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A matter slicer for any CNC

Discovered the Cricut via Ladyada the other day. She points to this instructable where Instructables user opendous makes solder masks using the “lowly” scrapbooking machine. I don’t need yet another machine sitting around the house, but I see that Cricut sells affortable blades and blade housing ready for CNC action. I’m ordering a Cricut Deep Cut Blade Housing to add foil and paper cutting powers to my micRoHere’s a nice picture of it. 

Interesting detail: The Circut is powered by an atmega-chip, just like the Grbl.

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Feb
12th
Thu
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Oy, vey! After nine months of community-informed hacking and development Lumenlab shipped the first three of their micRo desktop CNC mills today. See the full story in this forum thread.

Oy, vey! After nine months of community-informed hacking and development Lumenlab shipped the first three of their micRo desktop CNC mills today. See the full story in this forum thread.

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Last major feature in place: Helical motion

After completing the support for helical motion, the project has reached the point where it is theoretically feature complete. It supports all common g-code that I have seen in the wild. It does lines, arcs, helical motion correctly at the designated feed rate.

Grbl now uses a simple buffer mechanism to decouple the production of stepper pulses from the computations of steps. A couple of very precise timers control the generation of stepper pulses, and as long as the step computation keeps up with the steppers on average, the pulses will be generated in a rock steady pace. Especially setting up for a new circular movement is a heavy task for a tiny microcontroller like the atmega168. Thanks to the step-buffer it will have up to a couple of microseconds to complete the task without the motor controller missing a step.

All this is slightly theoretical at this point as I’m only testing the timing with a scope, waiting for my first CNC to arrive from Lumenlab

The next stage is to verify the design. I have written a test-rig in Adobe Air/Flex that emulates the CNC and lets me see visually that the motions generated is correct. Now I need to check that all movements are optimally precise and that it is able to complete full, real world machining sequences.

  • I will write a suite of tests to verify that it generates the precise, intended movements
  • I am going to expand my test rig to be able to feed full CAM-generated motion sequences and render the resulting tool-paths in some kind of isometric view.
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Testing Grbl on an Arduino Mini at 16MHz

Testing Grbl on an Arduino Mini at 16MHz

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