Group Assignment:

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Individual Assignment

What is CNC Machining?

CNC machining is an automated manufacturing process that uses computer programs to control machines. This includes machines like lathes, mills, routers, and grinders, allowing for the precise removal of material from a workpiece to create a desired shape. CNC machine operations eliminate human error and increase production speeds, ensuring high repeatability and accuracy.

How does a CNC machine work?

The CNC machining process involves several critical stages, starting from the design phase to the final finishing touches. Below is a breakdown of each step in the process:
Stage 1: Design & Programming
Stage 2: Machine Setup & Workpiece Loading
Stage 3: Machining (Cutting, Milling, Turning, etc.)
Stage 4: Finishing, Inspection & Post-Processing

Inspiration and Initial Idea

To begin the design process, I explored references on Pinterest to find ideas for a functional piece of furniture. My initial concept was centered around designing a chair. During this exploration, I came across a convertible multipurpose chair design. The concept was interesting because the chair could be folded and transformed into a ladder, making it a multifunctional piece of furniture. This adaptability and space-saving aspect made it an ideal inspiration for my project.

The reference design can be found here

Designing

The design phase turned out to be the most challenging part of the process.

My initial goal was to create a fully parametric design, allowing easy modification of dimensions such as material thickness, slot width, and overall size. However, the parametric setup repeatedly failed to behave as expected.

A major issue occurred with the slot width parameter. The slot width consistently became larger than the actual material thickness, even when I attempted to control it through parameters.

I attempted to fix this by adjusting constraints and modifying the parameter values several times.

Despite three to four iterations of modifying the parameters, the design did not behave correctly. Every time I updated the slot width parameter, the geometry updated incorrectly, resulting in misaligned or oversized slots.

At this point, my instructor reviewed the file and suggested that instead of continuing to troubleshoot the existing design, I should start with a completely fresh sketch.

Redesign Approach

Following this advice, I decided to redesign the model from scratch using a different workflow.

In my previous attempt, the entire structure was drawn in 2D sketches and then extruded into a 3D model.

For the new design, I changed my approach:
- I began by creating two basic structural elements in a 2D sketch.

- These base components were extruded into 3D geometry.

- From the extruded bodies, I then constructed the remaining features directly in the 3D workspace.

Using this method, I was able to complete the entire design in less than three hours, which was significantly faster compared to the earlier attempts.

Another advantage of this approach was that the parametric relationships worked more reliably.
When I adjusted parameters such as width or length, the model updated correctly, and the overall proportions remained consistent.

This felt like a major milestone in my design process, especially after the earlier struggles with parametric constraints.

Scaling the Design for Cardboard Prototyping

The original design was created based on the actual dimensions required for fabrication in plywood. However, before moving to the final material, a scaled prototype needed to be produced using cardboard in order to test the structure and slot fitting.

Since the cardboard sheet used for prototyping had a material thickness of 0.3 mm, the design had to be scaled down proportionally.

Exporting the Design To prepare the file for laser cutting, the following steps were performed:
I projected the sketch from the 3D model to obtain the flat geometry required for cutting.

The projected sketch was then exported as a DXF file.
The DXF file was opened in Inkscape for further adjustments and scaling.

Since the design was originally created at a larger size, I needed to calculate a scale ratio to fit the cardboard prototype.

The workflow I followed was:

use this link to access the ratio calculator.

Using the calculated ratio, I scaled the design proportionally.
The resized vector geometry was then copied back into Inkscape and placed on the working page.

Then i cut it in cardboard -

Final Result :

After finalizing the model, I measured the plywood sheet that would be used for fabricating the furniture. To ensure accuracy, I measured the material thickness at multiple points on the same side of the sheet and calculated the average thickness, which came out to 16.34 mm

Once the correct material thickness was determined, I rescaled the furniture design to the required dimensions. I then added dog-bone fillets to the internal corners to compensate
for the round cutting bit used during machining, ensuring that the joints would fit properly during assembly.
To create these dogbones, I installed a plugin from the Autodesk Fusion App Store called Nifty Dogbone for Autodesk Fusion. After installation, the tool appeared under the Modify menu as Nifty Dogbone.

Nifty Dog Bones: CNC router bits are round, so they can't cut sharp inside corners —
they always leave a small curve. This is a problem when two pieces need to fit together, since the mating piece has sharp outside corners that won't seat into the rounded recess. Dog bones are small circular cutouts added at inside corners so the bit fully clears the corner, letting mating pieces fit flush. The circle diameter matches your cutting tool.

After which you can arrange, project and export as a DXF file,ready for print.

Curv Settings
For setting up the CNC toolpaths, We used VCarve Pro – ShopBot Edition, which is the CAD/CAM software that works with the ShopBot machines at our lab. I started by opening VCarve and creating a new file. The job size was set to match the plywood sheet I was using — 8 ft × 4 ft — and the material thickness was 16.34 mm, which I got from measuring the sheet earlier. Once that was done, the workspace was ready.

To bring in the design, I went to File → Import Vectors and loaded the DXF file I had exported from Fusion 360.

The plywood sheet needs to be physically secured to the machine bed. The ShopBot has a sacrificial layer already on the bed, and the sheet sits on top of that.

Screws go through the sheet into the sacrificial layer to hold everything in place while cutting.
The tricky part is making sure the screws aren't placed anywhere the tool will travel — if the end mill hits a screw, it'll break. So I drew small 6 mm diameter circles from the left toolbar in areas that would be safe (away from any toolpaths), and created a drilling toolpath for them.

This is how the 3D Preview of our Drilling toolpath looks like:

For the slot features, I went to the right toolbar -> a Pocket Toolpath set to conventional — this makes sure the tool runs along the inner edge of the vector, keeping the slot dimensions accurate. The tool I used was a 6 mm single-flute end mill, with Cut depth 18 mm.

The last operation was cutting out the outer edges of each part, got o Profile Toolpath -> Outside Cut so the tool stays on the outer side of the line and the part comes out the right size.

VCarve did throw a warning saying the cut depth exceeds material thickness — but that was intentional, so I accepted it and moved on.

This is the 3D toolpath view:

Then I added holding tabs to some of the larger internal cutouts to stop pieces from moving around mid-cut.

I saved the toolpaths as two separate ShopBot Part Files (.SBP):

File 1 — the drilling operation only (for marking screw positions)
File 2 — the slot cutting + outer profile cuts

Keeping them separate so that I can run the drill marks first, physically screw down the sheet, and then run the actual cuts without any risk of the tool running into a screw.

Now I load the plywood sheet onto the machine. Then I clamp the workpieces onto the bed with the help of clamps and screws at the edge of the bed.

Then I loaded the drill program into VCarve by using the Start option.

Then I clicked 'Start' and ran on the spindle by clicking 'Ok' in the dialogue box. Then we have to wait for a few seconds so that RPM of the spindle stabilises. Then I click 'Ok' and the machine starts routing the workpiece according to the design provided.

Then I drill screws into each of these holes Then I moved the tool to one end of the machine and I took X and Y offset. For the Z offset we used a touchplate.

Now I wait for the machine to finish cutting all the pieces. It is important to wear all the required safety equipment, including gloves and safety goggles. In addition, safety headphones must be worn because the machine produces a high level of noise during the cutting process.