Week 7: Computer Controlled Machining

CNC machines are automated milling devices that manufacture industrial components without direct human assistance. They use coded instructions sent to a computer, allowing factories to make parts accurately and quickly. CNC machining is a "subtractive" manufacturing process that typically uses computerized controls and machine tools to remove layers of material from a blank (or workpiece) and produce a custom part. The automated nature of CNC machining makes it possible to create simple, high-precision parts with high accuracy; and to fabricate unique, medium-scale production series cost-effectively.

The CNC machining process begins with creating a 2D vector or 3D Computer-Aided Design (CAD) of a solid part. Once the CAD design is complete, the designer exports it to a CNC-compatible file format, such as STEP or IGES.

This week our task is to design, mill and assemble something BIG - preferrably something that doesn't need fasteners or glue and also incorporates curved surfaces.

I took this week to begin the "skeleton" of my final project, which happened to change direction just before this week's assignment. Also, as I was designing and preparing my file for the CNC, the literal form of my final project changed as well.

Here's the link to our Group Assignment!

Project files

I have been learning and using Fusion 360 throughout the course. I used it this week to design my piece and also incorporated a dogbone add-in that easily applies dogbones to files in preparation for milling. I then exported the sketch files to Rhino since we were using Rhino CAM to setup our designs for cutting.

Here are the files:

Test File

Screws

Down Cut

Up Cut

Milling on the CNC

I used a 10mm thick plywood board and had the machine cut an initial pass with a down cut end mill 6mm deep. I then switched that bit out for an up cut one to finish going through the board.

I went with a downcut/upcut combination to avoid ripping the wood fibers as much as possible and keep both sides of my pieces as clean as possible since they will be exposed in the final project. I also like avoiding wood fillers (only my test pieces were all down cut).

Settings

After the file was set, onto the Raptor!

Here's Josep adjusting the board referencing the edge on the sacrificial bed:

Zeroing the bit:

Test cut first:

Milling the rest:

Issues

The milling went smoothly and I began to assemble my pieces. Turns out, I encountered a major problem - the slots where my vertical supports were to fit did not align. Parametrically, the issue wasn't an equal distribution of slots on each horizontal piece, but rather the fact that I did not design my slots off of a shared reference plane, which in this case, is the inside face of the board the horizontal ribs press into.

In other words, if I stack the horizontal pieces on top of each other, the slots align, but that's only because the slots are distributed equally across each rib. Once assembled, their differences in length and in vertical distribution become painfully apparent.

4 more of these vertical pieces are cut and ready to go

Josep the instructor showed me how to redistribute/redraw the slots on my pieces on Rhino to then nest them on the remaining piece of plywood and setup once again for milling. I will go back and correct the slot distribution on Fusion360 to have a proper working file as well.

Takeaways

It was a long week - machine set ups take time and there was a lot of traffic in the lab. It was tough to plan ahead and prep files to cut while still learning to design on CAD.

Already, I knew my major limitation was the amount of time it takes me to design a file on Fusion, but I spent most of my time designing anyway because I wanted to cut my final project structure and didn't want to compromise.

Fab Lab is intensive and time goes fast.

Now that I went through the process, I can do it again (with guidance of course) and correct any mistakes. But I did find myself just accepting to I could not cut before the week closed. I have yet to cut the corrected pieces, but I am happy I got to go through the process and luckily the pieces are easily swappable.