Using the Software and the tools at TechShop, one can carve a contour map of virtually anywhere in the world!
The task is to create a three dimensional contour map of a specific region, in this case part of Pittsburgh, PA, located near TechShop. The 3D contour data was brought in from Google Sketchup and was then converted into machine file paths using a program called 3D Carve. These machine file paths were used directly by the Shopbot software to carve a block of foam into the contour map.
Step 1: Grab Region in Google Sketchup
Google Sketchup has the ability to directly access Google map information including contour data. Launch Google Sketchup, and then use the “Add a Location” button. You can zoom and pan, and then “Select Region” as desired. Then you can crop to the specific area and once the location is selected, you can crop out the area you want using the blue pins, and then click the “Grab" button. You can then rotate your selected region as needed.
Step 2: Add "Show Terrain" Shortcut
As an oversight to Google Sketchup, there is no default button to show terrain. So the next step will be to add a keyboard shortcut to access this command. Go to Window\Preferences\Shortcuts and filter on the term “Show Terrain.” Select “File\Geo-Location\Show Terrain” and create the keyboard shortcut Ctrl+Shift+T. I know of no other way to access this command.
Step 3: Unlock and "Explode" Terrain
Then, using the keyboard shortcut you have created, Ctrl+Shift+T, show the terrain for the region selected. From View Menu, select “Camera-Parallel-Perspective.” Left-click on your region, and then right-click, and from the popup menu select “Unlock.” When the bounding box becomes blue you will know that your terrain is unlocked. Left-click on the terrain, and then right-click, and from the popup menu select “Explode.”
Step 4: Create Rectangle Smaller Than Area Selected
Select “Camera Views Bottom,” to see the bottom of the terrain. Then, draw a rectangle larger than the bottom of the region. Select the scale button, and then double click the rectangle to “Shrink Less Than Area.”
Step 5: Project Rectangle Through Model
Orbit your region as needed so that you can see the rectangle below. Use the command, “Project to Above Surface,” extending your projection well above your Terrain Contour. Using the Selection button, right-click on the rectangle and choose “Intersect Faces With Model.”
Step 6: Select Extra Edges and Faces and Delete Them
Select extra edges and faces, and delete them using the eraser tool.
Step 7: Scale the Region to the Output Dimension Needed
Use the “Tape Measure” tool to make note of the limiting dimension. In order to scale the entire model, use a calculator to find the scale ratio, and redimension the model within a few feet of the final dimensions that you want. Since the initial model was scaled to the dimension of the actual region that you selected, perhaps hundreds of miles square, this scaling needs to be a two step process, as limited by the number of digits of precision that you can type into Sketchup. In this case, the limiting dimension was scaled to two feet, half the width of a four-by-eight foot block of foam.
Step 8: Delete the Man
Sketchup provides a figure of a man to give an approximate physical dimension of your model. This figure needs to be deleted or it will be explored with your object data. After deleting the man, the final step is to export your 3D model, saving as an OBJ file.
Step 9: Bringing the OBJ Data Into Cut3D
The next task is to convert your OBJ file into toolpaths that can be read by the CNC router. The software that I used is called Cut3D by Ventric. Begin by opening your OBJ file. The software takes you through a step-by-step process beginning with Materials setup. Select the correct dimensions for your project.
Step 10: Selecting the Rough Cut Toolpath
To begin, select the tool you will cut with. Since this project is cut in foam, I have selected a large bit, a high rotation speed, and a high feed rate and plunge rate. You will need to run this job MUCH slower if you are cutting denser material. To further speed up the cutting of this job, I have selected 3D Raster along the X axis, which calculates to a rough cut time of 1 hour 8 minutes.
Step 11: Selecting the Finishing Toolpath
For this step I have selected a ball nose bit, again with a high cutting speed, feed rate, and plunge rate. Since I was cutting in foam, I was not too concerned with overheating the bit or moving the router too quickly. I think that these settings are about as fast as I could go, however, since I began to create some burr in the foam. The Cutout toolpath can be ignored because we are not cutting anything out in this project.
Step 12: Carve Preview Machine Finishing
What is interesting is that in the Finishing toolpath preview, the polygonal surface that makes up the Google Map contour map is visible. It would be interesting to get contour data from another source to possibly eliminate this faceting.
Step 13: Preparing the Foam to Cut
Shown here, behind another one of my projects, is a 4x8 foot sheet of 2 inch thick construction foam. This cost me about $35 at a construction supply store. I will look for less expensive sources for this foam in the future.
I first cut the foam down to size on the table saw. I then glued two pieces of foam together to create one piece four inches thick, and applied weight to the top piece until the glue set. After the glue set, the foam was ready for carving!
Step 14: Anchoring the Foam to Cut
The next task was anchoring the foam to the Shopbot table. I used both double sided sticky tape and blocks of wood to hold it securely.
Step 15: Cutting With the Shopbot
Operating the Shopbot software is highly specific to this particular machine at TechShop Pittsburgh. I could create a detailed tutorial for using this software, but it would only be useful for people who already own this $25,000 piece of hardware. It will suffice to say that there were many steps to output this map to the router.
Shown are images at the beginning, middle, and end of the cut process.
I hope you have enjoyed this tutorial!