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Archive for April 4th, 2013

Makergear M2 vs. LinuxCNC: Project Overview

M2 - cushwa Owl - half scale

M2 – cushwa Owl – half scale

During the course of my Makerbot Thing-O-Matic experience, I concluded:

  • Enthusiasm may get a product out, but engineering makes it work
  • Plywood and plastic do not produce a stable 3D printer
  • Measurements matter
  • 8-bit microcontrollers belong in the dustbin of history

With that in mind, I’ve long thought that LinuxCNC (formerly EMC2) would provide a much better basis for the control software required for a 3D printer than the current crop of Arduino-based microcontrollers. LinuxCNC provides:

  • Hard real time motion control with proven performance
  • A robust, well-defined hardware interface layer
  • Ladder-logic machine control
  • Isolated userspace programming
  • Access to a complete Linux distro’s wealth of programs / utilities
  • Access to an x86 PC’s wealth of hardware gadgetry

Rather than (try to) force-fit new functions in an Arduino microcontroller, I decided it would be interesting to retrofit a DIY 3D printer with a LinuxCNC controller, improve the basic hardware control and sensing, instrument the extruder, then take measurements that might shed some light on DIY 3D printing’s current shortcomings.

The overall plan looks like this:

  • Start with a Makergear M2
  • See what the stock hardware can do
  • Replace the RAMBo controller with LinuxCNC
  • See what the hardware can do with better drivers
  • Adapt the G-Code / M-Code processing to use more-or-less stock Marlin G-Code
  • Add useful controllers along the lines of the Joggy Thing
  • Improve the platform height / level sensing
  • Rebuild the extruder with temperature and force sensors
  • Start taking measurements!

My reasons for choosing the Makergear M2 as the basis for this project should be obvious:

  • All metal: no plywood, no acrylic (albeit a plastic filament drive)
  • Decent stepper motors (with one notable exception)
  • Reasonable hot end design
  • Good reputation

The first step of the overall plan included a meticulously documented M2 build that I figured would take a month or two, what with the usual snafus and gotchas that accompany building any complex mechanism. Quite by coincidence, a huge box arrived on my birthday (the Thing-O-Matic arrived on Christmas Eve, so perhaps this is a tradition), the day when I learned that Mad Phil had entered his final weeks of life.

As the Yiddish proverb puts it: If you wish to hear G*d laugh, tell him of your plans.

So I converted a box of parts into a functional M2 3D printer over the course of four intense days, alternating between our living room floor and a card table in Phil’s home office, showing him how things worked, getting his advice & suggestions, and swapping “Do you remember when?” stories. Another few days sufficed for software installation, configuration, and basic tuneup; I managed to show him some shiny plastic doodads just before he departed consensus reality; as nearly as I can tell, we both benefited from the distractions.

Which means I don’t have many pictures or much documentation of the in-process tweakage that produced a functional printer. The next week or so of posts should cover the key points in enough detail to be useful.

Not to spoil the plot or anything: a stock M2 works wonderfully well.

Owl - half size - left

Owl – half size – left

For example, a half-scale cushwa owl printed in PLA at 165 °C with no bed cooling and these Slic3r parameters:

  • 500 mm/s move
  • 300 mm/s infill
  • 200 mm/s solid infill
  • 100 mm/s internal perimeter
  • 50 mm/s bottom layer
  • 30 mm/s external perimeter
  • 1 mm retract @ 300 mm/s

The beak came out slightly droopy and each downward-pointing feather dangles a glittery drop. There’s room for improvement, but that’s pretty good a week after opening a box o’ parts…

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