This week, our task was to use the plasma cutter to cut out the outline of a state, and then post process it so that it looks good.

Using the plasma cutter was easier than I was expecting, and it produced a much nicer result. I used it to cut out two Montanas from a thin sheet of mild steel. I chose Montana because it is pretty large, has some straight sides and some curves, and is just a pretty cool state in general.

After some technical difficulties and some resizing, and with some help, I was eventually able to successfully cut out my shapes. I set the feed rate to 110, and this worked well. My shape had very little dross. It looked like this:

Because it was mid semester break this week, I went home to San Antonio for the long weekend. I have a wood and metal shop, so I used the tools there to complete this project.

Despite the success with the plasma cutter settings, the shape still required a bit of surface treatment. There was a dark line around the profile, and the edges were pretty rough. To get rid of the dross, I used a metalworking chisel and a hammer.  I simply knocked the dross right off. To clean up the tiny amount that was left, I secured the shape in my bench vise and used a file.

With the dross gone, I still had to smooth the edges and remove that dark line. I used a Dremel to smooth out the ridges on the edges, and a wire wheel on the bench grinder to take care of the dark lines. Here you can see the shape before (right) and after (left) these steps:

At this point the pieces looked pretty good, but still had some grime and scratches on the surface of the metal. A random orbital sander with 220 grit paper cleaned this up pretty well, but there were some deep scratches and marks that I could not totally eliminate. With my piece already being so thin I did not want to sand it too much.

I knew that most other people would cut their states from aluminum and then spray paint them, so I wanted to take advantage of the fact that I cut mine out of steel and do something a bit different. I decided to try Bluing them. I had seen this done before with brass and gun metal, so I figured I could probably do it with this too. My original plan was to use a blowtorch, but since the two states had to be as identical as possible, I figured this technique would be too challenging. I did some research and found that you can blue mild steel at less than 500 degrees, so as soon as my mom left to go run some errands I quickly cleaned and degreased my shapes then put them in the oven.

Our oven only goes up to 485 degrees, so I kept my pieces in there for half an hour after it preheated to give them time to heat up properly.  I was not sure if this would work or not, but when I took them out they looked like this:

Some sources say to quench the shapes in oil, but others say its fine to let them air cool. Given that the strength and other physical properties of the steel did not matter, I decided to simply let them air cool for a few hours. Once they were room temperature I covered them with some Semigloss Spar Varnish. I am sure that other options would work better but this is what I had on hand, and it seems to work fine.

Interestingly, spraying the shape on the right made it turn a slightly more bronze color, while it left the color of the one on the left unaffected. When they were in the oven I used convection, and put them in right next to each other and for the same amount of time, and they were cut out of the same sheet of metal right next to each other, so I am not sure why they reacted differently. It is kind of cool though.

As I mentioned earlier, there are still a few imperfections on the surfaces, but they add to the rustic feel of the pieces and demonstrate how the imperfections react to the bluing process in different ways. The dark lines around the edges somehow came back during the bluing process. And although I very thoroughly cleaned the surfaces and was careful not to handle them with my bare hands before placing them in the oven, you can still see fingerprints. They show up as discolorations in the finish. Next time I will wear gloves throughout the entire process. Also, on the back sides it is very easy to tell where the pieces contacted the metal oven grates. I expected this and was careful to place the pieces with the correct side facing up.

Overall I am quite pleased with the result. This was my first time using a plasma cutter, and bluing steel. I learned a lot about both processes and now feel comfortable with them, and eager to try them again in future projects.