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7. Computer Controlled Machining

This week, I explored CNC (Computer Numerical Control) machining, which allows us to cut large sheets of material like plywood, MDF, and acrylic with precision. The goal was to design, prepare, and mill a large structure using a CNC router.

Part 1: Understanding

What is computer controlled machining?

CNC (Computer Numerical Control) is a way of controlling machines using a computer. Instead of cutting or shaping materials by hand, a CNC machine follows a pre-programmed design to cut, drill, or carve materials like wood, plastic, and metal with high accuracy.

Types of CNC Machines

CNC Milling Machine: A computer-controlled machine that cuts and shapes materials using a rotating cutter.

CNC Router: Similar to a milling machine but mainly used for cutting wood, plastic, and soft metals.

CNC Plasma Cutter: Uses a hot plasma torch to cut through metal quickly and precisely.

CNC Lathe: Spins the material while a cutting tool shapes it, mainly for making round objects.

CNC Waterjet Cutter: Uses high-pressure water (sometimes mixed with sand) to cut through almost any material.

Riidl CNC Machine

Our lab has the Numac Hitech CNC machine with a bed size of 8' x 4'(2400 mm x 1200 mm). It is a 3 axis machine, meaning it moves in the X, Y, and Z directions for precise cutting and shaping.

Here’s how it works:

  • You design on a computer using CAD (Computer-Aided Design) software. (I prefer working on Fusion)
  • The design is converted into NC programme, a special language that tells the machine what to do.
  • Once that is done you can load your material on teh machine.
  • A suitable cutting tool (milling cutter) is attached for the required job.
  • Then you can start the job and the machine moves the cutting tool according to the programmed design, removing material bit by bit.
  • The result? Perfectly cut pieces which will be ready for assembly.

Part 2: Group Assignment

This week's group assignmnet is uploaded on my friend Samruddhi's page

From this group assignment, I learned how to safely operate our lab’s CNC machine by first completing the safety training. I also understood how to test and fine-tune machine settings like spindle runout, tool alignment, fixturing, speeds, feeds, and toolpaths. Doing these test runs helped me see how small changes can impact the final outcome and machine performance. This process taught me the importance of careful setup and testing before actual milling to avoid errors and ensure good results.

Part 3: Project 1 - Making something big

The Idea

For this project, I designed a collapsible stool which draws inspiration from nature and Indian culture. The idea is to create something that reflects the beauty and simplicity found in the natural world.

The top of the stool is shaped like a "Phool" (Hindi word for flower), symbolizing the significance of flowers in Indian culture, often seen in rituals, festivals, and everyday life.

The legs of the stool flow like "leher" (Hindi word for waves), drawing inspiration from the natural movement of water.

Together, the flower and wave reflects the harmony between stillness and movement.

Bauhaus Influence

The Bauhaus movement is all about simple, functional, and beautiful design.

  • It is simple in form.
  • Every part has a function, making it practical and not just decorative.
  • Use of boldd primary colours

I have tried to incoperate all this in my design!

Creating the CAD Model

I used Fusion 360 to create a 3D model. This helped me finalize the dimensions, joints, and weight distribution.

I began by setting the parameters by defining the material thickness and the slot dimentions

After that I created a 2D sketch of the required shape, defining the key dimensions and outlines

The top of my table was going to be a shape of a flower so I designed a file in Illustartor and impored the dxf file in fuaion so that i get a perfect shape.

Problem: Earlier, the shape of my flower had more depth than what our tool could handle. I realized that with the available bit size, it wouldn't be possible to cut the design accurately. Solution: So, I modified the shape and reduced the depth to make it suitable for the tool, ensuring that the design could be machined properly without damaging the material or the tool.

The right one is the earler shape and the left one is the redesigned version.

Similarly I drew design of one leg in Illustrator to get the perfect curve. Imported it in Fusion and mirrorred and joined it to get the second part of my design.

Once that was done I created slotes and chafered it

I did the simliar procedure for the other part of the legs

Error: Earlier I made one pair of leg and then copied the same to get another pair. Later I realised because of this the slot was incorrect

So corrected and redesigned it

This is how the final model looks like

CAM and Toolpath Preparation

Once the design was finalized, I moved to CAM (Computer-Aided Manufacturing) to generate toolpaths for CNC cutting.

I laid out all the parts within a 6 ft x 7 ft rectangle—the size of my plywood sheet. I did this directly in Fusion 360. Then, I switched to the Manufacture workspace

Machine setup

In this tab, I defined the setup. Click on create “New Setup”.

Once you do this a dialogue box will apperar. You need to select the type of operation on what you are doing i.e milling and tehn set the origin of your toolpath.

Note: Make sure you your orientation matches with your machine’s orientation.

The Stock Offset is usually set to 1 mm to make sure the tool cuts properly around any imperfections. At this stage, you don’t add a post-processor, as the focus is just on setting up the material. Once the stock settings are done, the setup is complete

2D contour

Tool selection

For 2D contouring, a flat mill tool is typically used as it provides a flat cutting surface, ideal for contouring operations.

We used the 6mm flat endmill with a flute length of 20 mm and an overall length of 63 mm. Then we edited the length of the tool.

We disabled the “Coolant” as it wasn't there in our machine.

  • Each tool (based on the material thickness) has a default rate for feed and speed.
  • Cutting feedrate is generally between 500 to 1000.
  • I made sure the plunge feedrate did not exceed 400, as going higher can cause excessive heat and potentially burn the material.

This is the cutting data after changing.

Geometry

Under the Geometry section, I selected the path outline that I wanted to route, ensuring only the relevant areas for cutting were included.

Note: You have the option to either create separate toolpaths or combine multiple routes into a single toolpath. However, it's recommended to divide the machining into multiple toolpaths. This is because, if one route fails, the machining process will restart from the beginning.

Heights

For selecting heights in the setup, always start from the bottom of the material. Set the bottom height first (usually the base of the stock or model), and then adjust the top height, retract height, and clearance height accordingly. This helps ensure that the toolpath is aligned properly with the material thickness and avoids cutting errors.

Change Bottom Height to model bottom and retract height to top height

Passes

Under passes click of multiple depths. Set Max Roughing Stepdown as 3 mm if you are using Plywood.

Linking

You need to turn off the leads (lead in and lead out)

2D Pocket

For the 2D Pocket operation, most of the settings remain the same as those used in the 2D Contour process.

The only key difference is in the Geometry section.

In this step, instead of selecting an outline as done in 2D contouring, you need to select the inner pocket area that you want to clear. This tells the software to remove material from within the selected boundary, not just around it.

Once the pocket area is selected and all other settings are reviewed, your 2D Pocket toolpath will be ready.

And now your toolpath is ready!

Simulating Toolpath

You can preview your toolpath using the “Simulate with Machine” feature to ensure everything is correct before exporting. Just right click the toolpath and click on stimulate

Post the Toolpath

In order to post the toolpath select the toolpath, right click and select Generate nc programe

Under Post Configuration, select the machine post as RichAuto and choose the folder where you want to save the NC file.

Note:

  • Make sure to create the NC programs in the exact order you want the machine to cut.
  • Always cut the inner pockets first, followed by the outer contours. This ensures that the piece stays in place while cutting and doesn't shift or come loose.

Test cut

At first, I had kept a 0.5mm clearance in my design file — meaning the slot was 18.5 mm for a 18 mm thick part. But later I realised that ince plywood thickness can vary slightly I ahve to measure the actual sheet which is there in my lab. So I designed test cut pieces

Here’s how the final test pieces turned out.

Part 4: Project 2

I, along with the help of my friends Samurudhi Rovalekar and Kanika Kadam, designed and fabricated large 3D letters for TOSS, the annual sports event at Somaiya Vidyavihar University. The objective was to create a bold and striking installation that would serve as a visual centerpiece at Somaiya Cricket Ground, Sion.

We first sketched out the letters, ensuring they were aligned with the official TOSS branding. Using Adobe Illustrator, we traced the TOSS logo. This vector outline ensured our design could be scaled up without pixel disasters.

Once that was done the vector file was exported as a DXF and imported into Fusion 360 for proper dimensioning. Here, we adjusted proportions, alignment, and material thickness because nobody likes wobbly letters.

Before starting with the cutting we had to set up the manufacturing process in Fusion 360. This step ensured that the cutting paths, speeds, and depths were optimized for clean and precise cuts.

Once our design was ready it was time to cut out the pieces. The CNC machine milled the letters and after that we went out to asembled the pieces.

The Challenge: Working with Flex Ply

Unlike regular plywood, flex ply has a mind of its own—it bends, curves, and refuses to behave. While this material was necessary for achieving the desired shape. Clamping, aligning, and reinforcing the pieces required extra effort and patience. Despite the challenge, we successfully assembled the installation. And the last step was painting

The final Output