Computer Controlled Machining

Design Concept

I wanted to design a Charukasera-style furniture piece where kids( not just kids, you can too) can lie down, lean back, and relax comfortably. Since it is meant for resting, I wanted the furniture to feel warm, safe, and full of affection.

I really like how elephants show love. They gently lean their heads on each other and twist their trunks together in a caring way. That moment feels calm, protective, and soft — exactly the feeling I wanted children to experience while using this furniture.

Form development

The legs of the chair are inspired by the curved shape of an elephant's trunk.
These trunk-like forms extend and connect to the other leg and the footrest, visually representing two elephants standing close with their trunks twisted together.

I believe this connection provides structural support and also conveys a sense of bonding, calmness, and emotional comfort through the design.

Designing the Model in Fusion 360

I created the furniture model in Fusion 360 and worked on making it parametric so it could adapt to different machines and materials. This was the most challenging part of the process.

Before machining on the ShopBot, we produced a test model using cardboard on the Trotec laser cutter, which is why the material thickness should be in parametic. To manage this, I made the material thickness parametric in Fusion. This allows me to change the thickness anytime without disturbing the overall design.

To make the slots on the curved part, I drew an arc between the legs and created a 45 mm curved slot. The slot width was set to material thickness minus 0.1 mm clearance. Using a circular pattern, I made 9 slots along the curve, and added 35 mm slots at the bottom of the legs.

Support planks

I used a construction plane: mid-plane between the two inner faces of the chair legs and sketched the supporting piece on it. Then I extruded it symmetrically using half of the material thickness on both sides. After that, I used the Combine tool to create the slot for joining it with the main legs and added fillets. Once the back support was completed, I copied the same body to the front side of the legs, combined it, and added fillets there as well.

For creating the first plank, I made a construction mid-plane between the slots in the leg and sketched the plank on it. Then extruded it symmetrically and added fillets to the edges. After that, I used a circular pattern to create 5 planks, with the angle set to -103° and partial distribution, since I wanted to leave space in between for the other designed planks.

For the second plank, I followed the same process as the first one, but with a different design. After creating the plank, I used a circular pattern to make 4 planks, with the angle set to -77° and partial distribution.

To make the furniture more stable and give extra support, I added side support planks at the bottom using a tab-and-slot joint. I first made the support plank, then used the Combine tool to create the slots in the existing supports so the plank could fit into them. I also gave a 0.1 mm offset to the slots for a better fit. In the same way, I added a support plank at the back as well.

To hold the seating planks in place and prevent them from falling apart, I created pins that fit between the legs and plank pieces. I sketched the pin profile and extruded it, then used a circular pattern to create 9 pins with an angle of -103°. After that, I mirrored them to the other side.

Footrest

For making the side planks of the footrest, I wanted the form to look like two twisted elephant trunks. I first sketched the idea in my notebook and then inserted it into Fusion using Insert Canvas as a reference image. Based on that, I sketched the profile and extruded it, then added fillets.

To make the twisting trunk detail more visible, I created another sketch on the profile, created an offset to it, and used Thin Extrude with Symmetric direction, 2 mm distance, Wall Location: Center, and Cut operation.

I also used tab-and-slot joints to connect the footrest planks parts. On the front side, I created a similar plank design like the seating area plank on the chair, and then made the top plank to rest the foot.

For the top plank, I wanted to create an engraved effect. For that, I used the front plank design, first projected the sketch of the front plank using the Project tool, then exported it as a DXF file. I opened the DXF in Inkscape and exported it as an SVG file.

After that, I used Insert SVG in Fusion to import the design onto the top plank. I then gave an offset to the imported design and extruded it inward using a cut operation.

Laser cutting - joinery test

Before cutting the final plywood model on the ShopBot, tested the design using cardboard on the Trotec laser cutter. To check the fit of joints, dimensions, and overall assembly. This helped identify design errors early, saved material, reduced machining time, and prevented costly mistakes on the final plywood.

After measuring the cardboard at multiple points, I calculated an average thickness of 2.94 mm. I used this value to find the scale ratio for reducing the model from 12 mm to 2.94 mm.

The calculated scale factor was entered into the Scale tool in Fusion 360, and the thickness parameter was then adjusted to 3 mm.

Using the Arrange feature, I arranged all the parts within the cardboard sheet size of 410 mm x 270 mm. I kept the frame width as 2 mm and the object spacing as 1 mm to place the parts efficiently. After arranging them, I laser cut the pieces using the Trotec Speedy 100.

Design iteration

CAM: V- Carve

We used VCarve software to perform the CAM process and generate the toolpaths for CNC machining.

In VCarve, all vector sketches need to be joined and closed because toolpaths follow the vector boundaries.
For that click on each shapes, and check if it has closed pink dotted boundaries. If not, has to join the vector using join vector tool

Fixing the material to the sacrificial layer(bed) is very important before machining. If it is not secured properly, the material can move due to machine vibrations, which affects cutting accuracy and can even break the tool. It may also cause rough edges or the piece lifting during cutting. The sacrificial layer also protects the machine bed when the tool goes slightly deeper than the material.

To fix the material properly, we plan the drill holes in the CAM software itself. This is safer than drilling manually because we may not know where the internal cut pieces are located, and wrong drilling can damage endmill.

A single flute 6mm end mill tool was used, the cutting parameters were:

Feeds and Speeds

For cutting the slot inside the parts, I used a Pocket Toolpath operation,

I gave 18 mm as the cut depth, which is greater than the material thickness of 17.128 mm. Since the material thickness was uneven in different parts, keeping the cut depth slightly more than the material thickness helped to cut properly them throughout.

Before setting the next operation, I unselected the previously selected slot vectors and then selected the next required parts to apply the corresponding toolpath operation.

I wanted to create an engraving effect on the top surface of the footrest. For creating it, i used Profile toolpath operation:

I set the cut depth to 6 mm and selected Machine Vectors "On" so that the tool would cut directly on the vector.

For cutting the parts out of the material, I used a 2D Profile Toolpath. I set the cut depth to 18 mm and selected Machine Outside/right, so that the final dimensions of the parts would be maintained as designed.

I also added tabs to hold the parts in place during machining; as the machine cuts the outer profile of the parts, if it cuts all the way through, parts can move, vibrate, shift from the its position, or get hit by the tools.

After creating the toolpaths, I used the Save Toolpath option to export them. First, I saved only the drilling toolpath, since I have to make the drill holes first. These holes were then used to manually drill screws and fix the material securely onto the sacrificial layer.

After that, I saved the remaining toolpaths together, as all the other operations were done using the same 6 mm tool, and exported them with in .sbp file extension.