Guitar Rack build log

So, a few years ago I said I would build a guitar rack for my brother for Christmas. So I was a bit late, what of it?

Anyway, I though it would be cool to make the back plate of the rack something more interesting than a flat bar. Having just taken an oxyacetylene class at Techshop I decided to freehand cut a guitar outline out of sheet metal.

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The first step was to build a template. I searched google for a guitar outline and loaded it into inkscape. I traced the features I wanted to capture (Outline, pick-guard, and sound hole) using the bezier curve tool (just clicking points along the way, not worrying about getting the curves right.) I continued until I had an outline of the guitar body, neck, pick guard, and sound hole as separate paths. I didn’t capture screenshots at this point because I wasn’t thinking, so I’ve recreated these steps with a different image.

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Now, the lines I had were straight and it didn’t have the smooth curves that I wanted. I selected the path and ran path->simplify (ctrl+L) until the curve started looking better, and simplifying to a much better outline. After I simplified it to a smooth, repeatable shape.

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I then needed to scale my image so that it was approximately the size of a real guitar. I don’t own any, but google says a full size guitar is approximately 70cm. While resizing, take a look at the “height of selection” dialogue at the top of the window. (Don’t forget to turn the units to cm!)

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At this point, I was ready to lay out my outline for cutting. I changed the page properties in inkscape to be the same size as my sheet of metal (I used 24″ by 24″) and laid out my pieces. Note that you might want to extend the neck a little bit because you’ll need a bit of an overlap for the weld. I didn’t care about accuracy much, so here is what mine looked like. Just try to get them to fit on the page with minimal lost material.

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At this point I was ready to print out the template. Techshop has an awesome plotter that I could have printed this out in full size, but the paper is expensive and I wanted to make sure I had it right the first time. In retrospect, it would have been easier to do with the plotter.

If you don’t have a plotter, you can do what I did and install “posterazor” which will convert a raster image of known size into a paginated image with overlaps so you can cut off the margins and stitch it together. Save your image at full size as a .png. Note: the default resolution for png is different than the default resolution for posterazor. Instead of simply saving your file, make sure to go to “file->export bitmap…” and select the appropriate dpi.

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Open posterazor and select your exported file. Confirm that the output size is correct. Mine ended up being 30.00×30.00.Image

I used the default options for everything, except I chose landscape orientation because it would use less paper to get the full image printed. Make sure to choose the correct paper size. One sticking point is the ‘overlap’ that is inserted to make it easier to match up. If you have a pretty sparse image like above, it can be hard to index how far you overlap, and you might end up doing what I did and putting the outline together a little bit bigger than it was supposed to be. You could try selecting 0 overlap and cutting it out more precisely, but this isn’t rocket science.

After you’re done, you should be left with a nice paginated template that you can print, cut out, and tape together.Image

Make sure to wrap tape around the seams at the edges so you don’t get hung up there.

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Because my template ended up being a little bigger than it was supposed to be, it didn’t fit quite as well on the sheet as it should have. I decided to change my layout to make it a little bit easier to cut out. I suspect there was some error in the overlapping and there may have been some growth when we printed. This is where the plotter would have come in handy, because I suspect the sizing would be more correct.

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Tape down the template and outline with a sharpie.

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Make sure to get the spots where you taped as well:

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And finally, you should have a nice outline to cut along.Image

In retrospect, I really shouldn’t have butted the parts that close together. It ended up not mattering because the finished product was left rough, but being that precise is hard with a torch. A little wasted material is worth saving time and effort.

Another note, I tried to butt the flat edges up against the edge of the sheet, but again, because I left the edges rough, I had to blow a small chunk off the edge to match up the look. Move the part in a bit if you plan to keep a rough edge.

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After laying out the design in sharpie, I was ready to cut the the shape out. Thanks to the class I took, this was easily the most fun. Unfortunately, I couldn’t find the smallest cutting tip, so I ended up with a larger cutting flame than was ideal, and I probably didn’t make as fine of cuts. As I mentioned above, I wasn’t really worried about the edge finish because I was planning on grinding down the edge, but I really liked how it ended up with a more jagged edge.

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When I first started cutting, I kept bumping the oxygen knob shut and getting only a sooty acetylene flame and marking up the edge of the piece. Once I figured out how to hold it steady my progress was a lot better.

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I’m not very steady with the torch, but I got a lot better with it as I went along. It probably would have helped to practice a bit more first so the whole thing was more consistent, but I liked how it turned out.

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Cut one major line, and then broke up the scrap

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