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HOW TO BUILD AN IRON BALCONY PART ONE: CAD DESIGN AND PLASMA CUTTING.

Posted by Pedro Luis Sánchez on Feb 22nd 2020

The purpose of this blog article is to explain how we fabricate our balconies.

In the past, wrought iron was only forged by hand with hammers and heat. It was a skill of Titans. Nowadays the use of modern equipment makes our lives a lot easier. Or no? This first article explains the process of cutting the parts on the CNC plasma, starting with the AutoCAD drawing.

The first part is the CAD design.

We first make the drawings on AutoCAD, making sure we meet all the code requirements for a balcony. We have a base design that acts as a template for all balconies, and the only thing that changes is the looks.

We cut with our CNC plasma, many components of our balconies; therefore AutoCAD literacy is critical because to make things work, the CAD design has to be perfect. Any imperfections on the drawing will make the machine fail or cut defectively. For instance, if the drafter is not careful and leaves double lines, the torch will stop in the second pass. The plasma has a metal detector that cannot run on a space. It is also essential to catch broken lines because they will also make the machine stop or cut defectively. All the drawing has to be "joined"; this is all the lines need to be continuous. It seems obvious, but the cutting area cannot be larger than the plate size.

Another precaution is to leave enough distance in between pieces, ideally ½" is a good gap, but with care, one can leave up to ¼" in-between pieces. Special attention needs to be paid when it comes to narrow pieces, because they may warp during the process and cause "breakaways" that would stop production.

Once the CAD drawing is complete, now it is time to put it in a language that the machine can understand. CAD files usually are dwg files that cannot be read by the machine's brain. The cutter requires it to be a gm file. Now, dwg files cannot be converted into gms, at least with the software that the machine comes with; therefore, the dwg needs to be converted into a dxf file.

Once we have de dxf file, we upload the file to the machine software to begin the process of creating a readable gm file. This takes a few steps, which are merely "explanations" to the machine on what she needs to do. This also sets the cut speed into the program, and determines the type of "lead-ins" and "lead-outs"; that is to make the plasma pierce the metal outside the piece and make it approach the cut line in a way that does not damage the cut quality, or creates interference with other parts.

Once the gm file has been created, you can transfer it to the machine's computer via email or a flash drive. But after this has been done, do not think this click and go; a whole set up process has to take place, starting with placing the sheet metal plate on the plasma table. Turn on the compressor, turn on the plasma, turn on the brain, and finally turn on the computer 45 seconds after the brain. Make sure you patiently wait until everything loads up because if you start hitting buttons like crazy, all it will do is freeze the computer.

After that, the machine has to be programmed to recognize the position of the plate by moving the torch to its closest corner and hitting "align corner" and then moving the torch to the opposite side and hitting align edge. Now that the machine "knows" where the plate is, we are ready to find our "program zero position," which is interpreted as the closes point of the uploaded drawing.

When we align the piece, the program zero is set at the very corner of the plate, which is no good, because the torch will start cutting too close to the edge. Therefore it is advisable to move the torch ½" on either axis and then hit "set program zero." Now the torch can start in the right place.

After the machine is set, we can upload the job from the flash drive. But don't cut yet! We need to check the settings with the chart provided by the manufacturer to see if the parameters match the type of material we are going to be cutting. If you are cutting from a file that you have not used a while, it is essential to check the cut speed, and confirmed it is the right for the material thickness. Remember, the plasma table has an override that would allow you to reset the cut speed to the desired position.

OK, parameters are correct; but still, there is a precaution that needs to be taken: Inspect the torch to confirm the consumables are in good shape and are the right for the plate type that you are going to cut. Use a wire brush to clean the electrode and the other parts of the torch so that they look new and shiny. Don't forget to make sure the air pressure and quality are OK. To accomplish that, purge the water out of the air compressor and the air filter. Another essential thing to remember is to check the water level on the table; the water level needs to be as close as possible to the plate to ensure proper cooling of the cutouts.

Last but not least, make sure that the drawing fits the plate you are using by moving the torch to the farthest positions, especially when using partial sheets. The very last, hook up the ground clamp to the piece. Now you can go back to "program zero" and start cutting.

If all the parameters of the machine are correct for the material, the air pressure and quality right, and the program is perfect; just then, the plasma table will do its job without interruptions, and with excellent quality.