City Skyline

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I wanted to make something for my daughter's apartment in NYC. Since she likes big cities and was born in Chicago, I wanted to make something representing cities. In this case it's a back lit Chicago skyline. This project could be made using the laser cutter, CNC or a combination of both tools. The Shapeoko wasn't available yet, so the laser cutter was used. Yes, I know this is wordy....

Materials and Tools Used[edit | edit source]

  • 1/8 Birch Plywood (AC Moore)
  • 1 x 2" Pine Board (My garage or big box stores)
  • Flat black spray paint (Cheapest you can buy - Ollies)
  • LED strip (Various sources)
  • Sand Paper
  • Skyline Silhouette graphic
  • Inkscape (Available on Make717 computers)
  • Laser Cutter (Make717)

The first step is finding a suitable graphic to use for the skyline. Search google for skyline silhouette and you will find many examples. There are several considerations when looking for a suitable graphic for this project. First is the file type and resolution. Most of the file types you will find (JPG, PNG, BMP, etc) will need to be converted so they can be scaled and cut.

PNG and JPEG are the most prevalent formats you will find but you will have limited resolution to scale them up. BMP files should be ignored because they can't be scaled to any reasonable size. In my case, I was looking for something that could be up to 12" wide. TIFF files are good and have high resolutions, but the ideal format is SVG or Scaleable Vector Graphics. Rather than the graphic being represented as a bitmap, the SVG format represents it as vectors. This would be the similar to what 2D CAD programs do - their file formats are vector based.

<preaching> The final consideration is that the best files to use are ususally copyrighted works.  Someone created the design to sell and most of the better searches will take you to a commercial site.  While you can many times find a suitable "thumbnail" of a commercial graphic that can be converted and used, you need to think about your application.  What is the intended purpose?  If you're doing something commercially you definitely should be paying for the image.  A one off for personal use, that's up to you. </preaching>

One last comment about commercial works - sometimes it easier to buy something suitable then spend all the screen time converting and fixing the image to your needs. I used the cartoon chicago drawing from I find 123RF to be reasonably priced and they have on demand plans that fit my needs. I purchased the 40 credit plan for $39.

I downloaded the 2611 x 1607 pixels JPG version which was smaller than I needed but from experience I knew I could convert this to a vector with reasonable resolution. This also saved me one credit for future uses.

Inkscape[edit | edit source]

If you do anything with graphics, Inkscape needs to be in your toolbox. This open source program is my go to tool for 2D graphics. I've used it to rip and convert graphics, do simple CAD drawings, do sign layout for vinyl cutting, templates for scroll sawing, and drawing original artwork. This is not a tutorial on using Inkscape, just the steps I did to process the graphic.

  • Import the JPG into Inkscape (File->import) and select OK on the dialog. I almost never change the default values on this dialog.
  • Since the JPG is a bitmap we need to trace it and covert it to a path or vector. Select the image and open the Trace Bitmap tool (Path->Trace Bitmap...)
  • For this graphic, I converted it using the Brightness Cutoff scan with the default settings. Bit map tracing is as much art as it is science and every graphic is different. Many times you may need to try different settings or scan types to get a decent trace. All bit map tracing will result is some detail loss and the amount you are willing to accept depends on your application.

Bit Map Tracing

  • Once the graphic is traced you can delete the original imported image, leaving only the new vector drawing. At this point you have an "infinitely" scaleable image which I scaled to a 10.5" width - make sure you have the proportional lock on when scaling. Text or other graphics could also be added at this point or the graphic edited with the Inkscape tools.

Laser Cutting[edit | edit source]

While I could have made the skyline out of black opaque acrylic I went with wood because I'm cheap and it's more readily available. I also had some issues with the skyline design I chose and was glad I used wood because I had to repeat the cutting process a couple times. More on that later.

Inkscape is installed on the laser cutter computer so you can use your SVG file directly rather than saving it as a PDF. This is useful if you need to make changes based on what you see imported into RetinaEngrave.

  • In RetinaEngrave I changed the graphic outline color so I could cut all the windows and other details before cutting the outline. The details were so small that I used higher than recommend vector settings to make sure the small pieces fell out. Since I was painting it more burning on the wood didn't make a difference.
  • After cutting the first skyline, I realized a major detail was cut out of the skyline. The diamond shapes in the John Hancock building were not supported. One of these instances where the design isn't the best for laser cutting. I naively thought I could add some small connectors to hold the diamonds in place and not ruin the criss-cross affect. After two more tries and failures, I realized something different had to be done. I ended up using black thread and super glue (see photos below) to support the pieces from behind the board. The thread is small enough that it won't be noticeable.

Missing building sectionsThe fix!
Pieces removed when laser cutting and thread support attached using super glue

  • For the base I drew up the piece in Inkscape and used Vector Rastering to cut the slot in the wood. I would raster the base, check the depth using a small piece of wood and raster again to get a deeper grove. Each time I re-ran the raster I would bump up the z height to focus the laser a little deeper into the block. I cut about 1/2" into the block using this method. The Shapeoko would genearly be a better choice for this part.

Painting[edit | edit source]

Painting was pretty straight forward with three total coats. I should have pre-sanded the wood before painting as the the grain was pretty obvious even using flat black. I sanded the paint before the final coat to get a decent final finish. Since I needed to paint both sides I used a piece of thread to make a yoke allowing me to paint the front and back at the simultaneously.

Back Lighting[edit | edit source]

  == MORE TO COME ===