Week 7

Computer Controlled Machining

For this week's individual assignment we had to make something big using the CNC machine. The goal was to design, mill and then assemble the pieces. For this week's group assignment we had to test runout, alignment, speeds, feeds, and tool paths of our CNC machine.

A CNC machine is a motorized maneuverable tool and often a motorized maneuverable platform, which are both controlled by a computer, according to specific input instructions. Instructions are delivered to a CNC machine in the form of a sequential program of machine control instructions such as G-code and M-code, then executed. The program can be written by a person or, far more often, generated by graphical computer-aided design (CAD) software and/or computer aided manufacturing (CAM) software. In the case of 3D printers, the part to be printed is "sliced", before the instructions (or the program) is generated. 3D printers also use G-Code.

In our lab at Kochi, we have the Shopbot. Shopbot is a 3 axis machine the Z axis is perpendicular to the bed. The X and Y axis are the length and the breadth of the machine respectively.To have a rigid supporting layer on the bottom of the workpiece we will place an additional piece of plywood above the bed called sacrificing layer. The sacrificing layer also protect the millig bit from damage by avoiding unwanted intereference with the metal body. It can be used to cut timber, plywood, soft aluminum etc and has a bed size of 4x8 feet. She shopbot also has a dust collector that sucks in all the dusk while cutting. For reference, you can use the beginner's guide to using the shopbot . It is really helpful.

The shop bot has a few emergency switches to be used to turn the machine off at times of need.

     

Individual Assignment


For my individual assignment, I wanted to make a simple and something I can use. So I decided to make a shoe rack and table top without using any nails or screws. I started by sketching a simple design on my book.

I then went ahead and designed it on Autodesk Fusion 360. The design was simple and stable and used parametrics everywhere needed. Once the design was done, I had to add a few things additional, like adding dog bones, fillets etc.



Adding dog bones manually is a bit of work. So I installed the Add In for Dogbones and then added it to Fusion and used it for adding dog bones. This was easy. This is the link to the tutorial to use it.

When the dog bones were added and all changes were made, I rendered the image and cut it using laser to see if everything is perfect. The laser cut was done perfectly and it fit correctly.

You can download the CAD file from here

After the design was done and completed, I arranged the individual components on the sheet so that I can cut it. I uploaded the design file to the computer connected to the Shopbot. After rearranging the components again allowing screwing space, etc, I selected the mill, edited tabs, added ramps and all other details and generated the G Codes using VCarve.

I initially made a mistake of not cleaning the bed first, which showed a problem with the bed level. I had to take the wood out and clean all over again before starting the cut.

Once everything was set up, I started the cut, it took around 1 and a half hours to finish the cut.
As the cut was done, I had to sand it and assemble it. Sanding and filing were to be done to have a perfect fit in due to imperfections in the plywood.

Once the sanding was done, I started assembling the parts and press fits to build my shoe rack. This was a bit tough but was worth the effort, after a few minutes, the shoe rack was completed! This is how the final product looked like compared to the rendered image!

Group Assignment


This week We need a test runout, alignment, speeds, feeds, and toolpaths for our machine by part of our assignment. So for testing some parameters in shopbot, we have designed a structure in Fusion 360.






Once the cutting was done, we had the plywood filed and sanded the edges.



This was our group assignment to find the press fit dimension for the 12mm and 18 mm plywood .So we cut slots from 18.60 to 17.80 in steps of 0.1mm and for 12mm from 11.70 to 12.50 in steeps of 0.1 mm. We found out that the right press fits comes somewhere near 18.6 mm and 12.4 mm. The material thickness does vary a bit with temperature, moisture etc.