Jose Alegria - Fab Academy

Computer Controlled Machining

ASsignment

wHAT iS THE ASSIGNMENT ABOUT?

Make (design+mill+assemble) something big.

Group Assignment:

Complete your labs safety training

Test runout, alignment, speeds, feeds, and toolpaths for your machine

Document your work to the group work page and reflect on your individual page what you learned

1^st Step. Finding an opportunity/necessity

The first step is to find something big to build. The importance of the size in this assignment is to make something that cannot be done with the laser cutter. So, I was in the search for something that was big enough to be done with the CNC and that could be assembled without any external help (i.e., without nails or glue).

In our Fablab, we needed something to keep the students blueprints safe while rolled up, so I decided to make a container (600 mm x 600 mm) with space for papers and the rolled blueprints.

2^nd Step – Designing parametrically

As I was going to design a container, my needs were similar to the ones I had while designing a container for my Final Project. While that was a case with special needs such as having dry areas for the PCBs and wet areas designed to allow water through it, the container I need for this assignment is a lot simpler. I decided to use my original design as an origin for the new design, using the parametric settings made in Fusion 360, I had to change the size of the panels from 100 mm to 600 mm and the size of the joints according to the material thickness, for I was using a 3 mm acrylic for the final project case, and now I am using a 17 mm pine wood sheet for my assignment.

After that, I had to consider the differences in the cutting characteristics, for example, in the laser cutter I had to be aware of the kerf changing the width of the joints, thus rendering my press fit design harder to achieve. Here, in this assignment, the kerf could be taken of the equation by designing in such way that the CNC cuts the wood through the outside of the area to be used.

After changing the parameters according to the new needs, I exported the design to Autocad and made the final changes. For instance, getting all the pieces to fit in a 1.22 by 2.44 m wood panel.

3^rd Step – adjusting the design for the cnc cutting software.

After changing the parameters according to the new needs, I exported the design to Autocad and made the final changes. For instance, getting all the pieces to fit in a 1.22 by 2.44 m wood panel.

After that, I had to adjust the parameters in the CNC Controller Software. I was using VCarve to create a file that the machine could read. The first thing is to import our DWG file to the Software.

There were three different jobs that I had to create to cut the container: The first one was a set of borings made to create a dogbone effect and allow the parts to fit properly. I designed them to be just a hole with a diameter set by the tool I was going to use (0.25 in).

The second and third jobs were the main cutting procedure and was divided into two parts: the first passes and the final cutting to split the parts from the main board. These are explained ahead.

Inside the software I had to set the parameters which were:

Job type

- Single Sided

- Job Size: 1220 x 2440 x 18.5 (mm)

- Z Zero Position: Over the material surface

- XY Datum Position: 0, 0.

The next step is to set up the cutting tool I was going to be using:

Tool name: End Mill

Size: 0.25 in. or 6.35 mm

Spindle Speed: 12 000 RPM

Feed Rate: 6 500 mm/min

Plunge Rate: 3 500 mm/min

Cutting parameters: our cutting will be done with a step depth of 5 mm (It was programmed for three main passes with a depth of 5 mm, and a final pass of 3.5 mm).

This setting allowed me to set a faster Spindle Speed (6 500 mm/min) for the first passes, the last pass of 3.5 mm had to be programmed for a slower Spindle Speed of 3 500 mm/min to avoid the material to be moved once it gets separated from the main board.

Once the parameters are set, I let the software to provide the optimum cutting path and it shows it with a diagram

Now, we only need to export the settings as a gcode file that can be send directly to the CNC.

5^th Step – Setting up the Machine

To set up the CNC I needed to insert the cutting tool (0.25 inch cutter) and set a few parameters before starting the process:

- Set the lowest point to cut into (Function 24).

- Set the material thickness (Function 20).

- Set the origin coordinates (Function 10).

These parameters are set through the CNC Remote Control:

6^th Step – Cutting

The next step is to start cutting, I sent the instruction to allow the machine to drill all the dogbones before cutting, this was working fine until there was a problem with the cutter and it was broken during the process. I changed the instructions to cut first and then drill, this allowed me to get to know a different function: the machine can restart the job wherever you tell it to. The machine displays where it is currently working when you pause the job.

After that incident, the process went straight forward:

7^th Step – Assembly

In order to assemble the container, I took off the parts that had been cut and started cleaning them from burr by using a file, just to leave the assembly joints clean enough to be assembled. Then, I assembled it using a mallet and nothing else.

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Conclussions

This was the last assignment I completed. It was difficult to start the design but once I got the idea of what to do I was able to solve the main problems that happened without suffering as much as I predicted.

Original Files

If you wish to see or download the original files, click on the following links:

1. Nuevo Cubo Parametrico

Nueval Checklist

ü Linked to the group assignment page

ü Documented how you designed your object (something big)

ü Documented how you made your CAM-toolpath

ü Documented how you made something BIG

ü Described problems and how you fixed them

ü Included your design files and hero shot photos of your final object.

2022