In the last decade or so do-it-yourself auto fabrication has really taken off in the off-road world. Part of it has been driven by economics and part of it is due to interest in hobbyists building their own vehicles in their garage. The proliferation of quality manual tube benders has spurred rollcage and chassis projects, and other affordable fabrication tools have allowed home builders to do quality work. A common area of construction is that of cutting steel plate for making various brackets, mounts, and other more complex welded assemblies. If you’re like the average home builder, you make a cardboard template and set to work cutting out all your pieces from steel sheet using whatever tools you have available. These might include a bandsaw, hand grinder with cutting discs, some type of reciprocating saw, or a handheld plasma cutter if you’re fortunate enough to own one. Cutting holes may be accomplished with standard drill bits, or hole saws for larger openings. Cutting multiple matching plates can be time consuming and involve further grinder work to make a stack of pieces match well. Computer-controlled plasma cutters are a great tool for doing this type of steel sheet cutting and prices on small cutting tables has dropped. However, it may still be beyond your reach or need to spend thousands of dollars on one. An alternative we’ve used and may be available to you is that of using the resources of a fab shop to plasma cut pieces you design. We did just this with Rob Bonney Fabrication in Peoria, Arizona. Bonney has created modified oil pans, engine swap mounts, specialty body mount brackets, and numerous other custom requests for home builders. In the grand scheme of things, the cost is reasonable, considering the time savings versus cutting them all at home with less-than-ideal tools. And the finished product looks sharp.
Making curved or complex pieces from sheet steel can be very time consuming when done manually. Repeatability can be a chore as well. Complex or large curved shapes are easily cut on a plasma table, as are large diameter holes. The pieces also come off the cutter with nice edges so deburring is not needed.
For those of you that are CAD savvy and can draft up your pieces on a computer, you can typically supply a digital file to the shop that they can work with directly. Just check with them for specific format compatibility. Once the file is in the computer, it’s a simple matter to call it up and send the instructions to the plasma cutter now or in the future.
Oftentimes you can provide a shop with just a cardboard pattern of your design and they can scan the pattern into a computer file and adjust details as needed. Here’s a sample piece we needed that would have required multiple cuts on our bandsaw, plus the need to cut the large hole with a hole saw on a drill press. Once scanned, hole locations can also be manipulated for greater accuracy where needed.
All these specialty mounts were quickly cut out on a plasma table. Multiple holes were cut where we wanted to use mounting bolts, plus “speed holes” can easily be cut in the interior to reduce weight and add any appearance you may want. These complex shapes would have taken us a lot of time to produce manually. Smaller holes for bolts are often slightly under-sized as the plasma cutter cannot achieve as tight a tolerance for bolt holes as you might like. A quick clean-up with a reamer or drill bit can fine tune the bolt holes to an accurate final diameter.