Week 07: 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
Extra credit: use three-axis toolpaths

Here is my schedule!

Group Assignment

Introduction

For this week's group assignment, we explored the capabilities of the ShopBot PRS Standard CNC machine at our lab. Our objective was to understand the machine's specifications and safety guidelines, and to do a practical test by modeling and cutting a simple design.

ShopBot PRS Standard CNC — Specifications

Specification	Value
Workspace	2400mm x 1220mm
Speed	10,000 RPM
Software	ShopBot Control Software
Fixture	Clamps
Mechanical Resolution	0.015mm
Position Accuracy	+/- 0.127mm

Setting Origins: X and Y axes are set using ShopBot3 software with proximity sensors to detect material edges. The Z-axis is zeroed manually using a metal zeroing plate and clip — the machine slowly lowers the bit until it touches the plate to find the exact surface height.
Safety Features: Emergency stop button, reset button, start button, and main control box.

Safety Rules

Wear safety goggles and ear protection at all times.
Never leave the machine unattended during operation.
Keep hands, hair, and clothing away from all moving parts.
Use appropriate feed rates and spindle speeds for the material being cut.
Ensure the workpiece is securely clamped before starting.
Check that the collet and end mill are tight before every cut.
Always keep the emergency stop button within reach.
Clean the work area before and after use.

Modeling and Cutting

We designed a simple test piece in Fusion 360 and exported it as a DXF file. We then used VCarve to generate the toolpath and cut it on the ShopBot.

Cutting Settings:

Setting	Value
RPM	10,000
End Mill	6mm, 2 flutes
Material Thickness	15mm
Tabs	2

Conclusion

Through this group assignment, we gained valuable hands-on experience with the ShopBot PRS Standard CNC machine. We came away with a solid understanding of the machine's capabilities, safety protocols, and how to set up and run a cut successfully. Our final cut piece matched the design dimensions exactly, and the skills we learned here will definitely come in handy for future projects!

For more details, check out the full group assignment page here.

Individual Assignment

Hero Shot

For this week's assignment I decided to make a foldable bed table. I first sketched the design in my notebook just to get a rough idea of what I wanted to make.

After the rough sketch, I made a more detailed one with proper measurements.

Now the real challenge begins — I had to turn this sketch into an actual piece of furniture. For this I used Fusion 360 to make the design files.

I first opened Fusion 360 and created a new sketch.

After that, I started by defining the parameters for the table. This basically lets me set measurements as variables so I can easily change the dimensions later without having to redo everything.

I then made the table top by drawing a rectangle.

Then came the most important part — making the joint between the table legs and the support. This part was honestly a bit tricky because I had to calculate and play around with angles and triangles to get it right.

After finishing the joint, I moved on to making the table legs.

This is what the full sketch looks like at this point.

After finishing the sketch, I used the Extrude tool to give the table its 3D shape.

Lastly, to make the table look cleaner, I used the Fillet tool to round off the edges.

Here's how the table should look once it's fully assembled.

Laser Printing

Before actually milling the table, I wanted to test if the joint design actually works. So I exported the DXF file and printed it using the laser cutter. If you want to learn more about laser printing, check out my previous assignment here.

Here's the result from the laser cutter — and the joint works perfectly. YAY!!!!!

The CNC Machine

The ShopBot CNC Router (PRS Standard)

The ShopBot CNC router is an amazing machine that can slice right through all sorts of materials! It easily cuts through wood, plastics, foam, and even lightweight metals like aluminum.

Because it's so versatile, you can use it to make a huge variety of cool projects, including:

Custom furniture and cabinets

Intricate wood carvings and signs

Props for theater productions

Customized jigs and fixtures for industrial work

Information/Specifications of the ShopBot PRS Standard CNC

The CNC machine at our lab is the ShopBot PRS.

Specification	Value
Cutting Speed	150 mm/min
Cutting/Movement Area	266.7 x 124.5 x 20.3 cm
File Types	.EPS, .SVG, .DXF, .DWG, .STL
Mechanical Resolution	0.015 mm
Position Accuracy	+/- 0.127 mm

Safety Measures

"Look, listen, and smell" during operation — watch for smoke, unusual sounds, or burning smells.
Wear PPE (Personal Protective Equipment): safety goggles and ear protection.
Never leave the machine running unattended.
Keep hands, hair, and clothing away from all moving parts.
Tie up long hair before operating the machine.
Use suitable feed rates and spindle speeds for the material being cut.
Check that the collet and end mill are tight before every cut.
Always keep the emergency stop button within reach.
Clean the work area and store all tools and bits safely after use.

CNC Machine Software

After finalizing the design, I started milling the table using the CNC machine. I first exported the DXF file from Fusion 360 and generated the toolpath.

Now that I've exported my files, it's time to set up the CNC machine.

VCarve

I'm using VCarve to create my toolpath. You can follow along below.

Open VCarve and set up the width and height of your material.

Go to File > Import > Import Vectors and select your .dxf file.

To move your design, select it and click the move icon in the toolbar.

Go to Toolpaths > Profile Toolpath.

Keep the start depth at 0 and set the cut depth equal to the thickness of your material.

Go to Add Tabs to Toolpath > Edit Tabs, which opens the Toolpath Tabs window. Increase the number of tabs to suit your design — we used 2 tabs. Click Add Tabs, then Close. If the lines of a shape aren't recognized as one closed outline, select all the lines that belong to it and go to Edit > Join Vectors.

Press Close to finish the toolpath settings.

Save the toolpath file.

Milling!!

Before I started milling, I cleaned the bed of the machine and carefully clamped the plywood on the sacrificial board.

After that I opened the ShopBot software and imported my toolpath file. I set my X, Y, and Z origins. Now I'm ready to start cutting.

To set the Z-axis origin, we use the zeroing plate method. You can find it on our group assignment.

Finally I started milling the table.

Yay!! The milling came out clean!!

After taking out the pieces I noticed that the plywood I used had cracks in it. So I had to use glue and clamps to fix it.

After some time the glue dried and I was able to assemble the table. Note: I didn't use any glue or fasteners for this project.

Here is a short video of me assembling the table:

Yay!! The table came out clean!! I am so happy with the result. :D

Hero Shot

Files

Table design in Fusion 360: Table.dxf Table-legs.dxf

Link to my 3D model of the table

Reflection

This week I had a lot of fun with lots of learning. It was a very new experience for me to use the CNC machine and I really loved the things we can do with it. I designed and milled a table and I'm so happy with the result. I had a lot of fun this week - see you next week! :D ^-^