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Computer Controlled Machining

Group Assignment

Do your lab's safety training
Test runout, alignment, fixturing, speeds, feeds, materials, and toolpaths for your machine

Individual Assignment

Make (design+mill+assemble) something big (~meter-scale)
Extra credit: don't use fasteners or glue
extra credit: include curved surfaces

Design Process

Fusion 360

Chair Design
Slicer for Fusion 360
Cat Home Design

Testing

CNC Machining

ShopBot PRSalpha

Safety Measures
Machine Specifications

Cutting

Group Assignment

Click here: Do your lab's safety training

Test runout, alignment, fixturing, speeds, feeds, materials, and toolpaths for your machine

Design Process

During week three I had come across a parametric chair which I really liked. So I thought of designing that first and see how it goes.

Fusion 360

Fusion 360 is the go-to 3D designing software for me. The workspace and the workflow is very conveinent and easy for any beginner. I started 3D designing during Fab academy and Fusion 360 has been the best for me. Although, I'm still learning its full potential.

Chair Design

I wanted an egg shape to start off with my design, So I tried to get the shape. Then I trimmed off the remaining lines.

Then I trimmed off the remaining lines. Here's the egg shape.

I revolved the shape and revolved another egg shape for the seating and used boolean operation.

I cut off the bottom to get the shape like a bean bag.

Slicer for Fusion 360

I came across Slicer via various YouTube tutorials I had watched for furniture design. It seemed like an easy tool since it would slice any solid object and give the DXF file with all slots. Unfortunately, it is not supported by Fusion 360 anymore so I had difficulties to run it. But after a few tries, it opened.

I imported STL file of the chair design and gave construction technique as interlocked slices. I changed the height to 10 cm, since I wanted to make a prototype in cardboard first.

This software is very conveinent since it gives the assembly steps and as well as the plans.

I exported the DXF file of the plans to cut in cardboard.

Cat Home Design

My FAB mate, Kalyani shared this design of cat home and I really liked it. I thought of designing it incase the chair wouldn't work out.

I sketched it, I tried to arrange it in the plywood sheet to see if the material was enough. Few parts were missing and the material wasn't enough for this design.

I tried to make a few changes by removing few circles and the joints. Alas! The material still wasn't enough.

After a few iterations with my instructor, we reached this design. It looks similar but the radius of each circle is optimised for minimum material.

All joints will be pressfit

The design

Testing

Before Machining, it is important to test a prototype of the design to check if everything works out the way I planned it. I'll be doing a scale down version of the original design in Zund of the chair and the cat home.

The chair parts has been all cut.

Success! The chair has been assembled successfully.

But...

Even though chair was a success, the slicer couldn't give me a proper plan to cut in plywood. I tried different options but either the plans it gave me required a lot of material or for the optimised material, the shape wasn't received as expected.

So I had to test the cat home. Here's the cutting.

Here's the assembled version. Due to flexibility of the cardboard, the joints weren't fitting properly. Even after using a masking tape, the parts weren't fitting so my instructor helped to use thread so that one part stays strong. Likewise, 2 joints were threaded and assembled.

Here's the cat home (currently a wolf home)

Both of the designs together

CNC Machining

Now that I have completed the designing and testing, next step is the machining procedure.

ShopBot PRSalpha

The ShopBot PRSalpha is a top-tier 3-axis CNC machine renowned for its precision and reliability in woodworking. Its robust construction ensures stability and accuracy, even when handling intricate designs. Equipped with a range of high-performance spindle options, it effortlessly tackles various materials, from wood to non-ferrous metals. Intuitive software facilitates easy project design and programming, making it accessible to users of all skill levels. With its versatility and unmatched performance, the PRSalpha is the go-to choice for hobbyists, small businesses, and large-scale manufacturers alike, elevating woodworking projects to new heights with its exceptional precision and efficiency.

Safety Measures

Safety is paramount when operating your ShopBot CNC machine. In case of an emergency, the SPACEBAR on your computer keyboard functions as an immediate Panic/Stop/Halt button, halting the tool's movement instantly. Additionally, your ShopBot is equipped with a physical STOP Button, conveniently placed on the tool, which stops movement and, on a PRSalpha ShopBot or Buddy, cuts power to the spindle/router.

Read the manual thoroughly to familiarize yourself with the tool and its operation. Also, review manuals for the router/spindle mounted on your ShopBot.
Practice operating the ShopBot using the computer and ShopBot Control Software before engaging the router/spindle.
Prior to loading, positioning a workpiece, or adjusting the tool's position, always turn off the router or power tool. Avoid changing router bits or cutters without unplugging the power tool or ensuring it won't accidentally activate.
Secure the workpiece firmly to the work surface before cutting and maintain a safe distance from the tool during operation to avoid injuries from flying debris or broken cutters.
Never operate the tool when fatigued to maintain alertness and prevent accidents.
Wear eye and ear protection at all times when operating the ShopBot to safeguard against potential hazards.
Never leave the tool unattended while it's running to prevent unexpected cutting errors or workpiece slippage. Always maintain supervision during operation for maximum safety.

Machine Specifications

XY Move Speed (with full cutting force): Variable, max. 18.2m/min.
Z Move Speed (with full cutting force): Variable, max. 9.14m/min.
XY Positioning Speed: Variable, max. 45.7m/min.
Z Positioning Speed: Variable, max. 22.86m/min.
Step Resolution: 0.010mm
Linear Cutting Force: Approximately 68 Kg
X and Y Axis Drive System: Rack and Pinion
Z Axis Drive System: Rack and Pinion
Input Voltage: 220v single-phase, 230v 3-phase and 380/460V 3-phase power options are available, depending on tool and configuration.
The PRSalpha requires a fused disconnect installed by a licensed electrician. Spindle may require 3-phase.

Cutting

Dogbone

So before exporting the DXF file, one important thing is note is the addition of dogbones. It is a type of fillet added to the internal corners to get a complete clearance of the material by the milling cutter. End mills are round, so they cannot create perfect sharp internal corners. Without dogbones, the parts may not fit together properly due to the radius left by the tool. I downloaded the Fusion plugin Nifty Dogbone for this purpose.

Then, I projected the sketch face and saved the sketch in .dxf file format.

VCarve

The CAM for the toolpath can be done on Fusion itself. But as suggested by our instructor, Mufeed, we chose VCarve. VCarve is a CAM software for CNC milling and engraving. I imported my .dxf file in VCarve and gave the basic parameter values such as job size, origin, and material thickness. Before assigning the thickness value, I used vernier calliper to measure the thickness of the exact plywood I'll be using, and from the measurement it was clear that the thickness was varying between 11.7mm to 12.2mm.

So I gave 12mm as the thickness in the software.

Mill Bit: Single flute 6mm End Mill

It is important to clamp the plywood before cutting so that it doesn't move while cutting. So we use screws on the edges and parts were the material will not be cutting. It is better to give a separate toolpath for the positions than calculating the positions manually. So I provided the toolpath positions for pre-drill where the screws will be used.

I divided the milling in 4 parts: Drill (Pre-drill), Inner Cut, and Outer Cut.

Here is outer cut example

Here is inner cut example

Lastly I added tabs

Expected output

Switch on the ShopBot by turning on the main switch and turning the knob on the side panel of ShopBot.

When running a CNC tool, dust collection is an important consideration. It keeps both the air and the cutting area clean of dust and debris. We also have a remote for start, stop and emergency stop button.

Next step is to set the origin . For that, the module can be jogged along the X and Y axis to set the zero position. For Z axis, the machine comes with a plate and an alligator clip. The machine detects the position when the clip and the metal plate comes in contact and then automatically sets the Z axis's zero position.

When all the three axes are zeroed, then click on Cut Part to upload the file. Click on Start and then a pop-up box appears requesting to switch on the spindle. For that, turn the key provided at the side panel of the machine once.

Now press Start button on the remote and once the spindle starts spinning, click OK on the dialogue box. Likewise, three of my files were uploaded and the design was milled.

Next step is to get all the pieces out.

Problem

Unfortunately, 2 of the pieces were broken and additionally 2 other pieces were cut outside instead of inside. Therefore I had to recut 4 pieces.

Bigger Problem & SOLUTION

So the machine stopped while cutting the pieces. To my horror the driver of our machine was faulty and it would take a few days to fix it. Nevertheless, the pieces were cut in the mighty ZUND.

Post-processing

With all the pieces cut its time for post-processing which is sanding the pieces for a smooth finish.

Assembly

Assembling was a the hardest part. I faced the same problem I had with the cardboard cut pieces. Although all the pieces and cuts were correct, assembling more than one joint was nearly impossible. While assembling the second joint the first joint got misplaced and this problem repeated.

One joint even broke during the assembly and I had to cut it again.

Finally with the help of Midhun, Revi and Mufeed, my catpod was assembled.

Design Files

Files

Chair STL
Chair DXF
Cat Home DXF