Municipal Pattern




Introduction: Municipal Pattern

Design is integrated in our everyday urban environment, and while some is obvious in its aesthetic value, some objects we interact with on a daily basis possess strong design qualities as well. Municipal design is no different in the fact that whoever is creating utilitarian objects have to think about it's aesthetic integration into the world as in addition to its function. My work largely deals with appropriating many of these objects' design considering form, pattern, and material. This tutorial will give an example in adopting regular urban design for artistic purposes. This specific project will focus on the common tree grate found on many city sidewalks. The process incorporates drawing, digital fabrication software (Rhino) and equipment (CNC router), and wood working techniques.

Step 1: Picking Your Design

The first step in appropriating municipal design, is observing. If you walk around a downtown in many cities, you'll probably come across many utilitarian objects that you might not commonly pay attention to. A tree grate is a prime example of urban design that blends function with aesthetic properties. While the tree grate serves the purpose of irrigation and drainage, it also utilizes pattern work that is foundational to most architectural structures and environments. Many of these grates display a starburst like pattern cut into steel. Most urban centers intentionally combine beauty into its utilitarian backdrop as it adds value to the city's visual culture. I like tree grates for their intricate pattern work that varies in different models of the object. First you should observe and document a tree grate patterns that you appreciate. The objective of the project is to use the pattern you like and apply it to a more crafted material, in this case wood. Once you've chosen the design you like, you should use a tape measurer to measure the area of the tree grate's parameter as well as distances between cut ray lines in the metal.

Step 2: Drawing the Object

For this project I've decided to model my piece after a four panel tree grate with two distinct pattern types that create a continuity. The first step to creating the wood carved sculpture is to choose and use a CAD program on your computer. This drawing will later be input into the CNC router's software and cut with machine accuracy. I tend to use Rhino, a great 3D rendering program that allows you to draw three-dimensional objects at different view points. For this type of project, another vector drawing program will work such as Adobe Illustrator. We'll only need to draw the pattern from a 2 dimensional view, or from a bird's eye view. First assign your drawing program's units of measurement, in this case I use inches. Using Rhino's rectangle drawing function I can precisely draw a rectangle the same size as one of the tree grate's individual panels. As the two central panels have semi circles cut out of them, I'll want to next create that semi-circle in the drawing. First I find the midpoint of one of the lines of your drawn rectangle and from that point I create a circle using Rhino's circle tool. Make sure the circle matches the measured diameter of the actual tree grate centered semi-circle. Using the split tool on Rhino, you can isolate and delete one half of the circle you've created as well as the center line that divides your full circle. Highlight all of the lines of your remaining rectangle and the semicircle and make them one whole object using the join tool in Rhino. This will act as the parameter of the piece of wood you'll be carving your pattern out of on the CNC machine.

Step 3: Drawing Your Curved Marks

Now start drawing your lines that the CNC machine will be cutting out of the wood. You can do this by working with half of the panel. Since the object's design is symmetrical, you can draw half of the pattern and later symmetrically duplicate it on the other half of the panel. We'll start with the curved lines directly around your semicircle of the panel. Since the CNC machine will be carving material out of your wooden panel, you'll need to create a closed loop line. The ovular shape you'll be drawing should have curved ends as the CNC machine has difficulty cutting hard edges as it uses a spinning router bit. You can create these ovular shapes using the the circle tool again and splitting the circle up into spaces where each cut mark begins. Once you've drawn half of these curved marks, you can use the mirror option in Rhino to duplicate the marks you just drew on the second half of the panel.

Step 4: Creating the Straight Lined Pattern

Next, create additional circles from the midpoint of the semicircle that space out the starting points of the straight ray cuts. This will create layers of cuts that mimic the pattern of the tree grate. Again, you only need to draw on half of the panel. Additionally, create a parameter within the rectangle so that your straight lined elliptical shapes won't extend off of your panel when using the CNC machine to cut. You can use the mimc option to symmetrically duplicate the same pattern on the second half of the rectangular panel. Once you're satisfied with the pattern work on the lower half of your rectangle, mimic the pattern on the upper half of the rectangle. Delete any of the circles and lines you drew to create parameters for your pattern. Lastly, select the entire rectangular panel with the semicircle opening and use the mimc option to create your second panel.

Step 5: Finishing the Drawing

Now that you have the two central symmetrical panels, the last two rectangular panels will be easy to create as they require less pattern work and are free of the semicircle cut. First create another identical rectangle to the first panel you drew. Next, use the center of either semicircle you've already drawn and create additional circles as starting points for your for your straight lined elliptical marks. Additionally you'll need to create a parameter within your rectangle again so that the CNC router doesn't cut over the edge of your wood panel. Start drawing your straight lined ray marks on the lower half of the rectangle. Once you're satisfied with the pattern on the lower half of the rectangle, select your marks, and again use the mimc function to replicate the pattern on the upper half of the rectangle. Delete any extra lines or circles you use to create a parameter. Finally select that entire rectangular panel along with the interior pattern, and mimic that panel using the center of the semicircle on the first rectangular panel you drew. This will create a matching end panel for the left side of your your sculpture and thereby complete the entire tree grate shape and pattern. When all is said and done, select your entire object, making sure that you've moved the left corner of the image to the 0 point of the x and y axis on your Rhino program as the image will transfer to the same point on your CNC editing program once you've exported it. Select file and then select export selected. Name the file and save it as a dxf.

Step 6: Making Your Tool Path

Now it's time to use the CNC vector editing program. For this we will use the software V-Carve, which for the purposes of planar carving is completely adequate. Once you've opened V-Carve, select the option to open an existing file, in this case the dxf that you saved. The image should transfer to the V-Carve window and prompt you with some questions. It will ask you to verify the dimensions of the drawing as well as the thickness of the material you will be carving into. To give this piece a full 3-dimensional feeling, we'll be carving into 3/4" plywood, so assign a 0.75 thickness value. You'll also want to confirm that the router bit will be starting its cut on the top surface of the material you'll be cutting into. Also make sure in the "xy Datum" box you click the left bottom circle as this will correctly orient the image as to where the material you're cutting into will be. Make sure to confirm that the units of measurement are in inches. In order to cut the panels out efficiently, we'll be cutting each panel individually. Select the first central panel you drew and move it to the 0 point of the x and y axis, which will be obvious as the there is a white rectangular box that your drawing fits into. Select only the pattern work inside the panel and Choose the open tool paths tabs option under open tool paths. There will be a tool path button that you can click on. This will prompt you with more options to confirm. In this box you'll see a cutting depths box, tool box, machine vectors box, ramps plunge moves box, add tabs to tool path box, a position and profile name box, and a calculate button. You'll want to assign the cutting start depth at 0.0 which means the router will start plunging at the top surface of your material. The cut depth will tell you how deep you want the router to plunge entirely and depending on the depth of the material, V-Carve will automatically assign how many passes the router should make to safely and fully cut through the material. You can manually assign how many passes you want the router to make, but to be safe just let the program assign the standard amount of passes depending on the bit and the spindle speed. To make sure that the CNC router fully cuts through the material, assign the cut depth slightly greater than the actual thickness of the material. In this case, we'll assign a 0.77 cut depth. Given the fact that we're just cutting into plywood, just select an end mill tool in the tool selection box. The tool should have automatic settings for its spindle speed and feed rate. Again, you can manually change, but for this project, let's leave the automatic settings on. You don't want the rpm speed to be too slow with a feed rate that is too high, which can cause your router bit to break. You also want to make sure you're selecting an end mill bit that does not exceed the width of the elliptical shapes it will be carving into. A 1/4" bit is pretty standard and fairly safe from breaking providing you don't alter the bit's speed and feed rate settings in a damaging way. Next you'll want to select the correct machine vectors option, which is basically asking you how you want the router to cut your lines. You can select an outside, inside, on the the line cut. Since you are carving away material within your elliptical marks, you should select the inside cut. For this project you don't need to worry about the ramps plunge move box or the add tabs box. Now you're ready to calculate. Hit the calculate button and V-Carve will automatically calculate a tool path for your router to cut and specifically title this tool path. The window will also show you directional arrows and green points to show how the router will move on your material. Close the tool path window and you'll notice on the tool path tabs screen that there is a box named profile 1 checked. That is the tool path for the internal pattern work. Click on the button that looks like a hard disk. This will save your tool path as a v-carve file. This tool path is ready to use for cutting with the CNC router.

Step 7: Making Your Tool Path Part 2

After you've made the tool path for the internal pattern work, you'll want to make a tool path for the entire panels exterior parameter in order to accurately cut the panel to size and to cut the central semicircle. Un-check the profile 1 box in the tool path tabs window. Click on the tool paths button again. This time only click on the exterior parameter of the panel. Keep all of your cutting settings the same except for to options. For the machine vectors box, click on the outside cut option in order to make sure the panel will be cut to the accurate dimensions. Additionally, in the add tabs box, click the option to add tabs. This is to make sure that the panel being cut out will be connected to the material that the machine is cutting into. This is to prevent the panel from shifting out of place when the router is cutting it away from the entirety of the material being cut into. With no tabs the panel has nothing to hang onto once it's cut out of the material being used. Once you've added the tabs, click calculate, and again V-Carve will calculate a cutting path for the outer parameter of the panel. This tool path is now designated as profile 2. Again save this tool path but with a different title. Since the two central panels are identical, one pair of tool paths is adequate for the cutting process. You can basically run the same sets of cutting paths twice. Next you'll want to assign tool paths for the two end panels of the piece. All you need to do is repeat the steps you took with the central panels for these two end pieces. Calculate the internal pattern work first as one tool path, and the outside parameter as another. These will be saved as profiles 3 and 4. Now you're ready to cut. Open the software that operates your CNC machine. In this case we'll be using a ShopBot.

Step 8: Cutting the Object Out

When you're choosing your material to cut the municipal material out of, it's important to consider the relationship of that material to the general function the tree grate communicates. The tree grate combines an elegant pattern in an industrial material. If cutting the pattern out of wood, the type of wood can communicate different things. Since I'm trying to elevate the importance of the pattern and the object itself, I'll use a nice decadent wood grain. Since I'm using plywood because it matches the form and shape of the actual object, it's important to use a decadent surface ply. In this case I'm using cabinet grade red oak, as the grain stands out and has a finer quality than say pine. You'll want to buy two sheets of 3/4" red oak ply, and cut it down to four rectangular pieces that are slightly larger than the actual size of your anticipated panels. Depending on the CNC machine your using and its bed, there a couple ways to fasten the plywood to the MDF bed. If your CNC machine has a vacuum table, the pressurized suction can lock your plywood down to the bed. If you don't have a vacuum table. you can simply put a screw in each corner of your plywood piece and since the section of plywood I'll be cutting is slightly larger than the anticipated panel I'm cutting, the screw won't damage the actual piece. Once your plywood is fastened to the bed, it's time to open up the CNC machine's software program. This will allow you to manually move the router to the position of the table you want it to be at. It's important to be able to do this so that I can zero the point where I want the router to start cutting. In this case I want the router to start cutting at the bottom left corner of the material. First make sure you have attached an end mill router bit. Once that is done, I need to zero the point at which the router will cut. To do this, you first must manually move the router to the point where it will start cutting and be oriented to the dimensions of the object. Once the router is moved in the correct location along the x and the y axis, you can manually zero that location with your CNC program. To zero the z axis, which is the depth that the router will start cutting, you can use a sensor plate that is included with the CNC machine. Place the plate under the router bit that is already in the correct x and y location, and use the zero z axis function with your CNC program. The machine will lower the bit to the plate, taking into account the plate's depth and will then know where the material's top surface is. Once every axis is correctly zeroed it's time to start the router. Turn your ventilation on. You'll have an option to run a saved tool path, preferably the first one that you saved, and the machine will automatically starting moving and cutting in the path you saved it to make. Your first tool path cutting job should be the internal pattern work of the first central panel you saved. The machine will take its time to safely cut out the material and once done it will return to it's origin point. Don't unfasten your piece of ply. It's already zeroed to the points you want it to be at for the next cutting job. Next run your tool path for the exterior parameter of the panel. This will take much less time, and since we've added tabs, the panel will remain secure on the bed. Once the machine has finished its exterior cutting job, it is now safe to remove the panel along with the extra exterior material its attached to by the tabs. The tabs should be thin enough that you can either snap the panel off or hand saw through the tabs. We've successfully cut our first panel. You'll be able to repeat this same set of tool paths for the next piece of ply, but remember you'll have manually re-zero your originating cutting points as your new piece of plywood will have shifted slightly from the position the prior piece of ply was in. Once that's done, you'll repeat these steps for the two end pieces of the grate.

Step 9: Assembling Your Object

Once you've successfully cut one of your patterned panels, repeat the process on the second panel, being mindful of which surface side you want to have exposed to the router. After the second identical central panel is cut, repeat the process with the end panels. Be sure to use an air compressor to blow out any excessive dust caught in your cut marks. Once all cuts have been made and dusted, you should have a completely modular wood cut piece. You'll want to set the panels up in order to see how the grain best matches and to mark where you'll connect the panels' edges together with wood domino joints. Once you've made your marks for the connecting points, you'll use a domino joiner to cut matching incisions into the edge of the ply, making sure that each connecting incision along the edges will match precisely with its corresponding domino cuts. Once each domino cut has been made (you can decide how many you want to make) and you've inserted the dominos, you can push the panels together along their edges. They should fit snugly.

Step 10: Hanging the Object

Since I'm attempting to elevate the value of the industrial object, I find it appropriate to treat it in an exhibiting way. I find that by hanging it on the wall it achieves this new fetishized state, treating like a valuable wall hung painting. In order to do this I need to insert a hanging apparatus into the newly constructed tree grate. An efficient way to do this is by drilling two shallow holes on the top edge of the ply and inserting threaded grommets. Use some epoxy and make sure that the grommets sink into the plywood flush with its edge. Give it time to cure and once dry, you can easily screw in eye hooks. This will allow the tree grate to be hung from various hanging hardware. It's easy to hang the piece panel by panel by screw hooks. The piece translates a new meaning to the originating object's design, pattern, and function.

Step 11: Using Municipal Design

There are multiple variations of these types of municipal objects that can be appropriated for artistic purposes. To me it's not just a matter of taking something utilitarian and making it decorative. To me the appropriation sheds light on the already existing intentional design in everyday objects and our comfort and subtle recognition with them. These objects are ordinary to us, but I'd like to think that part of our conditioning to them is not only because of their function, but because of their physical appearance as well. The purpose of appropriating these designs is to show that there is beauty and further use for the mundane, banal, and common. They inform us of our culture and re-using them for sculptural purposes shows that we are aware of their existence and how they fit into our everyday lives.

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    3 Discussions


    4 years ago

    Interesting design inspiration; nice work!


    4 years ago

    I see those grates all the time and never gave them one thought. Now that I take some time and look at the photos they really are very pretty designs. Great instructable. Thanks for sharing!