3 vehicle nearly-build from polarbrainfreeze

Continuing the discussion from Design Challenge #1:

Forum regular and Glowforge talk show cohost @polarbrainfreeze posted an SVG of three separate car designs in the Design Challenge forum. I’m working late tonight so I decided to let a print run while I was cranking away.

Sadly this one didn’t come out perfectly, for a few reasons that weren’t Ben’s fault, and really amount to “we haven’t told you how to design for Glowforge yet” (although I know @tony is working to get that to you). As a result, there were a number of problems, which included:

  • lines that were doubled up, so the laser cut the twice - like the doors on the camper van
  • lines with ambiguous intent, like the blue outlines around the flames
  • things that looked like one thing but were problably another thing, like blue “lines” that were actually very narrow filled rectangles (the bottom of the red window area on the camper)

Again, this is all on us, because we haven’t shared best practices for GF design, so please don’t take it as a criticism! I just wanted to share why this one didn’t work. I’ll see about giving it another go during laser thursday. :slight_smile:

And because even a first attempt can be interesting, here’s how it looked before and after. You can see the double-cuts in the darker areas, for example all around the van pieces.

Next time!


Very nice! (did he include acrylic windows?) Also can you tell us (if you know) what software @polarbrainfreeze may have used to create his design before saving as SVG?

It looks like what I think are the steps (I’m confused, it’s not labeled “steps:” :wink:) are: engrave, cut, cut. What is the reason for the separate cuts? Best I could figure is proximity to other cuts, but there are other close cuts.

Are we going to see anything assembled, or will that be laser Thursday material?

Indeed and thanks!

It might be useful to add a preflight script that will check for shapes that have a fill AND stroke (did you really mean to cut and engrave?), and for lines that are doubled (which is usually a bad thing).

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@polarbrainfreeze wanted some lines scored and some lines cut through. My guess is the first cut is a lower power vector cut to just score the material.


To those who are Laser Savvy. I’ve seen this around other discussions about “designing for a laser” and there have been pointers about “double lines” as @dan pointed out (areas where two boxes overlap and “share” a single line). Can anyone explain this a little bit more for those of us who have never had the pleasure of using a laser?

If I have a double line drawn that the laser has previously already cut through, why wouldn’t the second pass just sit in the same kerf and not actually touch the material?

I’m interested in all of these kinds of details and I’m VERY excited to get the “GF best practices” pointers from @Tony. I want to design things ahead of time, but I definitely don’t have the knowledge base to do it “right”.


Very cool! Sorry I made the file so complex. :slight_smile: As you said, I was not sure what colors/line widths/etc to use for the GF. Once I know that it will make it easier.


I’m using Fusion 360 for the design, then I used InkScape to color the lines and areas.


I took a good look at the cut file. It looks like some of the details I designed are too small. If you look at the grill for the truck, there should be little “struts” going up and down. But I think I made them too thin, and they will not survive the laser-cutting. Same thing with the “vents” at the back of the van, behind the windows.


Thank you @dan for doing the print and posting with such a helpful explanation. And thanks to @polarbrainfreeze for the design work. Yesterday I rediscovered an Instructable 10 Tips and Tricks for Laser Cutting and Engraving that I had forgotten about from last fall. For those who are new to the design and work flow of lasers (me!) it explains and illustrates what @dan is pointing out and we hope that @Tony can get to us soon. I hope geordie_h from ADX hackerspace in Portland doesn’t mind my synopsis:

  1. Preparing for cutting and engraving
    a. Masking
    b. Presets
    c. Test runs
  2. The power of layers in the design software
    a. Controlling order of cuts by layer
    b. Have multiple parts and designs in layers instead of multiple files
    c. Add some guides in a non-printing layer
  3. Wood grains and engraving
    a. Growth rings in grain make contrasting engravings
    b. Design and print for veneer thickness
  4. Overlapping lines in nested layouts
    a. Two butted or overlapped figures with shared edges will have a shared double cut or engraved line and may waste time and burn edges
    b. Join the bounding paths and eliminate one.
  5. Raster versus vector Engraving
    a. Know the difference in design (raster/bitmap image versus vector path/line)
    b. Understand how head travels (zips back and forth in progressive lines versus follows contour path) and process times
    c. Know power and speed settings
  6. Defocus for thicker vector lines
    a. Instead of rastering a thick line, defocus the laser and use a vector
    b. Issues with resolution and crispness of edges
    c. Longer burn time at corners
  7. Add a vector to a raster engraving to sharpen edges
    a. Outlining the image gives a different effect
  8. Hitting the target
    a. System for cutting small scraps
    b. Glowforge camera makes it easy
  9. Engraving multiple objects
    a. Layout grids
    b. Jigs and fixtures
  10. Using the red dot (head positioning and travel)
    a. What red dot? We got cameras!

And that right there is 75% of my motivation for getting a glowforge!


Double run in a line you cut away is not so bad. Mostly just wasted time. There is a chance you cause excess char on the surface because of settings things in your honeycomb on fire for a while.

The main problem with double lines is when you did NOT want to cut through the material, so now you have an engrave that is either extra deep (and doesn’t look like the other lines), or you have a cut where you wanted an engrave.


Double cut lines also tend to have a wider kerf, so if you are doing assembly the parts may not fit as well.


Very interesting, thank you to all involved. Dan, would you recommend a practice run on cardboard first, so that people can see if there’s any issues, before using expensive materials? Would that catch all the issues, or would there be things that still can’t be discovered until you run it with the final material?

if you have double-lines on a file that you are sending to a vinyl printer, the second pass will often cut through the backing, which can create problems.
So if you are making a design that you want to be cuttable by ALL the CNC-type processes, you would really want to avoid doubling up. I don’t know offhand what other issues would be present with a cnc plasma or rotary cutter (other than wasted time) but I’m sure that some exist.

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Great hopper fodder!

I somehow missed his notes on this!

The extra heat tends to cause an extra-wide kerf and a great deal of charring.

It depends on what you’re testing for. With catalog prints and proofgrade materials, you can expect it to work perfectly. If the design is one you’ve run before on proofgrade and you run it again, ditto. But if you’re working with a design that might need adjustment - because you’re iterating on it, or it comes from someone else, or something similar - then the test print is important to see if the design is what you really wanted.

This could have been caught in its entirety by watching the cut simulator (you could see the double lines being cut) but I wanted to kick it off quickly and was OK with learning by printing. :slight_smile:


Lots of good info here. Thanks @dan

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Cut simulator…brilliant!


How long does the cut simulator take? If it’s real-time like other laser drivers I’ve found I’d just rather run the job & see what happens. I know it impacts tube life and uses up material but watching a real-time simulator feels a lot like watching golf on TV.


It’s some large multiplier of realtime - 10x or something?