Engraving HDPE with Shapeoko


Today I tried a more "artistic" engraving, but since I don't have any visual art talent I substituted programming for art.

 

My workflow's basically:

  • draw an SVG using svg.js in jsfiddle
  • export the drawn SVG using the SVG Crowbar Chrome bookmark
  • resize and customize the design using Inkscape.
  • open the design in MakerCAM
  • create CAM "follow path", calculate, export gcode
  • open GrblController, connect to CNC
  • position end mill justttt touching the top of the HDPE at the bottom left corner, set the position to "home"
  • turn on my dewalt 660 spindle
  • run the G-Code
  • sand, cut, wipe off the remaining burrs.

The designs are written using SVG.js and jsfiddle. I'm just using hacky perspective math.  Here's the two I cut:

Here'a another one I'm working on (called gravity):

The key thing, if you look at the code, is that I'm using polyline to make connected line segments. Originally I made separate lines for every segment, but then MakerCAM generates gcode where the spindle will raise up and down between every segment, and we want continuous cuts for each segment.  Otherwise it'll look bad with all the starts and stops.

I'm using a 2-color HDPE sheet from Inventables. It's 0.05" black on top of 1/4" white HDPE.  It comes in 8x12" sheets, so I used my trusty MasterCraft wet tile cutter saw (without being wet) as a small table saw to cut the sheets into 4 6"x4" sheets.

So, to summarize, what went well:

  • wet tile saw works great to cut sheets to desired size
  • I cut 0.01", 0.02", 0.03", 0.04", 0.05" lines as an original test to determine the best cut depth.
  • My workflow works, so I can iterate on designs and cut them within an hour.

What needs improvement:

  • I need a way to finish the designs and remove all the burrs without sanding the crap out of the HDPE.  The 3d plane cut shows how much I wore down the design trying to clean it up, no good.
  • My final designs are simpler than what I originally designed.  I'm using a 60 degree engraving bit, which isn't very narrow, so by the time I cut through the black layer I've got a pretty wide cut. So my designs need to be simplified.  A 10x10 grid is reasonable, a 20x20 grid is too detailed.  And I should consider either getting a steeper engraving bit, or consider trying to engrave painted wood instead of 0.05" HDPE to build these designs.
  • The bottom left of the second design is screwed up because, uh, I had my CNC, vacuum, space heater, light on the same power bar as my outside christmas lights on a timer.  The christmas lights clicked on, which overloaded the power bar, which shut off the CNC.  When I turned the CNC back on it went berserk and cut that random path.  Oops :)
  • My gcode always has very slow jog movements when repositioning the spindle for the next cut.

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