How to Turn an Image Into a Metal Sign/Stencil W/ CNC

I often have people asking me to make custom signs from their logos/imagery, so I decided to do this Instructable article on the process I use to turn a regular .jpg picture into a .tap file usable by CNC programs, then cut it into a piece of physical art to hang on the wall!

Supplies

This is the least expensive/simplest method of creating .tap files that I have found. You'll need:

Programs:

Inkscape (free online)

Sheetcam ($150 one time license, very worth it!)

FireControl (or your machine's control software)

Tools:

CNC Plasma table

Computer to run the programs and CNC table

Pliers (to handle hot metal)

Flap disc (to clean dross from cut metal)

Spray Paint (or let it rust for a neat patina!)

Step 1: DuckDuckGo the Image

I hopped on my favorite search engine and found an image I wanted to create signage out of. How about the Instructables robot!

Step 2: Open File in Inkscape, Resize

Download, install and fire up Inkscape. Open the picture by using File > Open and selecting the file. Then resize the image to the size sign you would like to end up with. Do this by selecting the image and then editing the H: and W: fields on the toolbar. Use the lock icon between the fields to constrain the dimensions and keep the image from being distorted. I chose to make this robot 12" tall. Then go to File>Document Properties and select Inches as your display unit. Then resize document to fit drawing or selection and save the file.

Step 3: Trace Bitmap

Select the image and go to Path>Trace Bitmap. In the menu that pops up, select single scan and hit Okay. You can then use the Edit Nodes tool to select the image and see the nodes that the bitmap tracing has produced. Save file as .svg.

Step 4: Check Nodes in Sheetcam

Open up sheetcam, create a new project and open your .svg file with the nodes. You'll likely see a whole lot of artifacts/noise as well as the issue of some details not being connected to anything, which makes them subject to just falling out of the piece when cut. All the red outlines in sheetcam indicate that a piece will fall out separate from the sheet. We can see that the face and chest details on this will not work as they are, we need to edit nodes to connect pieces together so the final product remains one piece.

Step 5: Clean Up the Nodes

Go back into inkscape and use the "Edit Paths by Nodes" tool, 2nd one down on the left side toolbar. Click on the nodes and hit DEL to delete them individually, or click and drag to select mulitples, then hit DEL to remove multiples at once. Go around the entire image and remove all the unnecessary nodes. Any node left will be a point that the plasma cutter cuts on. There is no point to having tons of tiny cuts inside something else that will be cut out, so delete them.

Step 6: Check Nodes in Sheetcam, Again

Save the edited .svg file and reopen that in Sheetcam. Now you'll see there is much less going on with the extra nodes cleaned up, but we still have to make sure the inside cuts don't just fall away from the finished piece. Next steps will show how to join/cut pieces together and each time it's best if you save and reopen it in Sheetcam to see how your Inkscape edits are affecting how Sheetcam sees the piece. Here we see that I still have some more minor artifacts to clean up in addition to connecting everything together, so back into Inkscape.

Step 7: Edit Nodes to Join Objects

Use the create rectangles tool to, well, create a rectangle. We're going to use this rectangle to join the robot's eyes together so that the one eye doesn't fall out separate from the piece. Once you've dragged the cursor to create an appropriate sized rectangle, you can click on the corners to resize it, or click again to change the corners to pivot the rectangle. I used pivot to try and match the angle of his eyebrow/mouth. After placing the oriented rectangle where I'd like to join objects, click Path>Object to Path. Then select the rectangle with the Edit Nodes tool and Shift+Click on the other piece to be joined, this will select the nodes of both pieces. Then go to Path>Union and the pieces will be joined together. We can then save and check in sheetcam to see what our changes have done. Here you can see the eye has changed from a red outline to a yellow outline, indicating that it is connected to our workpiece and will not fall out now. I did this again to the mouth and the chest details.

Step 8: Edit Nodes to Separate Objects

We might also need to delete some line, or create breaks in the lines, to join areas together. Perhaps I don't want the face separate from the body, so I can create a break in the line using the same rectangle trick as above, but this time using Path>Difference. This deletes/rearranges the nodes and usually there will be some offset/jaggedness on the edge. I'll then zoom in on the cut area, delete any extra nodes, then use the smooth node handles to straighten the lines by pointing them towards the next node.I can then save and check in Sheetcam to see the changes. This technique can be used to create stencil letters from other fonts, to keep the insides from falling out of enclosed letters like B,D,P,O,Q,R, etc.

Step 9: Go Over Entire Image, Joining/Separating As Necessary

I then went over the rest of the file and edited any parts that would fall out of the finish piece. I connected the ground between the robot's wheels for stability. I also connected his chest details to the edge outline by using the same rectangle/union technique. I also often save and check the progress in Sheetcam to make sure it's behaving as I expect it to.

Step 10: Create Toolpath and Post Process

After the .svg file is modified to my liking, I'll open it one last time in Sheetcam to finish converting it to a usable .tap file. I select Operation>Plasma Cut and then select the options for the material I'm cutting. This is where you'll need to do some tinkering if you've not already set up your CNC tool specs in sheetcam. I created a profile for each different metal/thickness that I cut, then use those tools to process the .svg. Here I'm using 1/8" steel sheet, so I select the parameters that the table my plasma machine recommends for that thickness. Once it's generated the toolpath with these parameters, I zoom in and check the toolpath, make sure it looks like it has enough clearance and is doing the things its supposed to be doing. Once I'm satisfied, I click File>Run Post Processor and save the file as a .tap

Step 11: Load File in CNC Software and Cut

I use FireControl, as it's the software that came with my Langmuir Systems Crossfire Pro, but this should be similar for other company's software. I load the .tap file into FireControl and set the program origin to align with where I'm going to physically start cutting on my sheet. Once it's aligned, I click Enable Torch and then Start. Now to watch the machine do it's thing!

Step 12: Clean Up Dross

As the torch cuts, the liquified metal goes somewhere and that's mostly into the water tray underneath, but some gets stuck to the work piece. To clean this up, I simply use a flap disc wheel on my angle grinder and go over the piece lightly. If there are inside cutout pieces that didn't full separate, I bang on them with my pliers and then bend them back and forth until metal fatigue breaks them off. I sand both sides this way and then it's ready for paint.

Step 13: Paint

Now that it's all cleaned up, I hit it with a coat of primer and then a color. This yellow isnt quite Instructables' signature shade, but it'll have to do! Also, this sign doubles as a stencil, which is pretty neat! The techniques in this Instructable should let you modify most any picture into a .tap file for CNC usage. Hope this has helped you, best of luck with your projects!