A CNC Plasma Cutter is a great tool for quickly and accurately cutting arbitrary shapes out of metal plate stock. This Instructable shows how we used a plasma cutter to create an address number plaque. We made it at TechShop and you can too (learn more at http://www.techshop.ws).

Tools Required:
• CAD graphics program (we used CorelDraw X5)
• Plasma Cutter (we used a Thermal Dynamics A60 CUTMASTER)
• Welders Chipping Hammer
• Safety glasses
• Drill Press
• No. 16 Wire Drill
• 82-degree Countersink bit
• (optional) Powder Coater (we used an Eastwood Dual Voltage Powder Coating System)
• (optional) Industrial Oven (we used a unit made by Ted’s Fabrication)
• (optional) Sink with hot and cold running water
• (optional) Respirator
• (optional) Chemical-resistant gloves
• (optional) Small scrub brush or scuff pad
• (optional) Oven-safe glove

Materials Required:
• 12” x 18” x 12 gauge mild steel plate (unfinished bare metal)
• Plasma Consumables (we used Thermal Dynamics’ Electrode 9-8232 with 40A Tip 9-8208 and Shield Cap 9-8245)
• (optional) Powder Coat Paint (we used Cardinal Paint polyester TGIC powder, T241-BK59)
• (optional) Bare wire (we used 16 AWG for the plaque and 22 AWG for the mounting screws)
• (optional) Cleaning agent (we used TSP)
• (optional) 4ea #8 x 2” stainless steel screws

Step 1: Design the Plaque

Before you begin the project, make sure to familiarize yourself with the basic operation of your equipment and the general safety precautions recommended by the equipment manufacturer.

Using CorelDraw X5, we designed our plaque to have a finished height of 6 inches while allowing the length to vary as needed for visual aesthetics. The attached pictures show the fundamental steps in the design process.

Step 2: Break Curves Where Characters Intersect Bounding Rectangle

By default, the plasma cutter will run a continuous cut path along every line and curve (collectively we’ll just call them “vectors”) in the design file. In order to prevent the individual characters from being completely cut out from our plaque, we need to delete the portion of any vector where the plasma cutter should stop cutting. As an example, the following picture sequence shows how we prevented the plasma torch from cutting the bottom of the ‘6’ away from the bounding rectangle.

Step 3: Lead-in Lines and Optimize Vector Order

When designing parts that will be fabricated using a plasma cutter, you can ensure that all cut edges on the final part will be as uniform and sharply-defined as possible by keeping the following two plasma cutting characteristics in mind:

• The diameter of a piercing hole will be noticeably larger than the width of the cut kerf
• The right edge of the cut will be more nearly perpendicular to the top surface of the metal than the left edge of the cut (“right” and “left” edges are determined relative to the direction that the plasma torch head is moving during the cut).

Since we wanted to have the highest quality finished edges on our plaque, we added lead-in vectors to allow the torch head to create pierce holes away from the finished part edges. We also adjusted the directions of all vectors so that the finished edge would always be made from the right-hand side of the cut (in essence, this meant cutting out interior edges using a counter-clockwise torch travel and exterior edges using a clockwise torch travel). Finally, we reordered the vectors to make sure they were cut in the order desired.

Step 4: Export the Design File in *.dxf Format

The TorchMate 3 software used to control the plasma cutter can’t interpret native CorelDraw (*.cdr) files but it can work directly with .dxf format. After completing the design and saving a native *.cdr version, we used CorelDraw’s “File\Export…” menu item to export an AutoCAD R9 .dxf version of our design as the following picture sequence shows:

Step 5: Preview Cut Path and Edit G-code

Before making any cuts with the plasma torch, we reviewed the entire cut path on the computer using the “Preview” mode to verify that:

• The torch will cut along the path expected
• The cuts will occur in the vector order expected
• The torch will be moving in the direction expected
• The torch will be creating pierce holes only where expected

Also note that any point where the plasma torch movement appears to momentarily pause before continuing along a cut path will result in a wider kerf at that point. This unwanted pause behavior can be easily corrected by directly editing the G-code within Torchmate 3.

As the attached file “Cut_PreviewB4GCedit.mp4” shows, the torch appeared to pause in a few unexpected locations such as while cutting the right-hand side of the ‘6’ where it intersects the bounding rectangle at the very top and bottom.
In reviewing G-code on the Torchmate 3 system, a continuous curve should consist of:

• A single {START} line
• A “G00” code line to jog the torch head to the pierce hole position and set the travel speed
• A series of “G01” code lines specifying the X- and Y- coordinates of points that trace out the entire curve
• A single {END} line

A pause will usually be the result of an unnecessary and unwanted {END}/{START}/G00 sequence within the series of G-code lines. As you watch the Torchmate preview, be sure to take note of the G-code line numbers scrolling in the G-code window when unexpected behavior occurs so you can locate those lines quickly in the G-code editor.

To remove a pause, double-click anywhere in the G-code window to open the G-code editor. Locate the suspect line numbers noted during the cut preview, select the offending {END}, {START}, and immediately following G00 line, then press the keyboard “Delete” key to remove the lines.

As the attached file “Cut_PreviewAfterGCedit.mp4” shows, the torch no longer pauses unexpectedly after the G-code has been edited to remove unwanted lines of code.

Step 6: Cut Test Pattern and Optimize Cut Settings

We included the cut quality test pattern in our part design file, so we used the G-code editor to delete everything except for the test pattern vectors. Then we cut our small star test pattern to check the cut quality before cutting the final part. The following Torchmate settings gave a very nice finished edge on our 12 GA mild steel using 40A plasma consumables:

• Arc Voltage: 111 volts
• Torch Working Height: 0.24 inches
• Travel Speed: 65 inches per minute
• Initial Piercing Height: 0.24 inches
• Pierce Delay: 0.2 seconds

Step 7: Cut the Part

Since we deleted the part coordinates from the G-code in Step 6, we loaded the G-code file saved earlier and then used the G-code editor to delete the test pattern coordinates.

The plasma cutter took less than 3 minutes to fully cut out the plaque and the cut edges seen from the top side were very clean and sharp.

Step 8: Drill Mounting Holes and Remove Dross on Backside

Our address plaque requirements specified provision for mounting using #8 oval head screws, so we drilled a clearance hole in each corner using a No. 16 drill and then added countersink to each hole.

Although the top surface had no visible splatter, the bottom did have a small amount of dross that was easily removed by lightly striking the dross with a welders chipper hammer.

Step 9: Apply Desired Protective Finish

Since our address plaque is intended to be mounted outdoors, we opted to apply a powder coat finish. For detailed instructions on how to apply power coat, check out our Instructable on Lamp Refinishing at: https://www.instructables.com/id/Lamp-Refinishing/