Week 7: Computer-Controlled Machining

MAKING BIG THINGS.

Week 7 Assignment:

1. Group Assignment

   1. Do your lab’s safety training
   2. Test runout, alignment, fixturing, speeds, feeds, materials, and toolpaths for your machine

2. Individual Assignment

   1. Make (design+mill+assemble) something big (~meter-scale)

3. Extra credits:

   • Don’t use fasteners or glue
   • Include curved surfaces
   • Use three-axis toolpaths

Learning

• Milling: rotating tool, tool moves over workpiece to produce arbitrary shapes (mill)

GROUP ASSIGNMENT

Our group will meet in April to complete the group assignment.

CNC Milling Machine Information

TIANCHENG XINLI Wood CNC engraving machine TC1325B

The Shenzhen Tiancheng Xinli CNC wood carving machine is a CNC device designed for woodworking, capable of automated carving, cutting, and milling. It offers high accuracy and efficiency, making it ideal for furniture production, woodcraft design, and panel processing.

INDIVIDUAL ASSIGNMENT

Since the actual printing will take place in April, I completed the design this week and tested a small-scale print using a 3D printer.

Note

Initially, I planned to use Autodesk Fusion or SOLIDWORKS for CAM. However, I could not access my student account for Fusion, and SolidWorks does not run on my MacBook.

In this project, I will use OnShape to design the 3D model.

Information (CAD & CAM)

1. CAD (Computer Aided Design) - computer programs or online applications (apps) to design the object

2. CAM (Computer Aided Manufacturing) - a software that converts a digital design into instructions for machines that manufacture parts

3. Machine Fabrication - a machine executes the instructions

Searching for Inspiration - I have a sofa and a small table at home, but the table is too short. Bending down too much causes my back to hurt, so I decided to make a tabletop that would allow me to work on the sofa without straining my back.

Then I found these on Pinterest:

Source: pinterest.com

For the second idea, I want to make a side table to put the Wi-Fi router on: Source: pinterest.com

Designing CAD model on OnShape

Note

I had some difficulty designing the joints because this week’s group assignment has not yet been completed. As a result, I did not know the design rules, the wood thickness, or the radius of the end mill (tool size). For now, I will refer to last year’s group assignmentas a reference, which used 18 mm thick high-density wood and an 8 mm end mill radius.

Model 1 - Table Top

At first, I designed the prototype/miniature size so it could be printed using a 3D printer.

1. Designing the table leg

   I created a joint on the top part and a joint hole in the middle of the leg. I made the bottom part thicker and also created a larger base at the bottom so that it would be more stable.

   

   Then I set up the parametric design as shown below:

   

   After that, I mirrored the leg so that I had two legs:

   

2. Designing the table top

   Next, I designed the tabletop and created the parametric design:

   

   I created two joint holes on the left side:

   

   Then I mirrored them to the right side:

   

3. Designing the middle support

   The last part is the middle support, which acts as a central structure to make the table more stable. This is the parametric design:

   

   I created three rectangles: one for the main part and two for the joints on each side. Then I deleted the redundant line in the middle using the Trim tool.

   

   Next, I used the Equal constraint so that the lines on the left and right sides of the joint have the same length.

   

   This is the final part:

   

4. Extruding the parts

   I extruded all of the parts and added a depth of 1.8 mm. The miniature model is 10× smaller than the real size.

   

   

5. 3D printing

   Finally, I exported the model as an STL file and printed it using a 3D printer.

   

Adjusting the size to the real size

After testing the miniature model, I adjusted the design to the real size. I scaled all of the dimensions to be 10× larger than the miniature model.

In this step, the parametric design was very helpful. I only needed to change the parameter values in the table, and the whole model automatically updated to the new size.

Adding T-Bone / Dog-Bone for the joints

Because CNC milling machines cannot produce perfect right internal corners, it is important to add T-Bone or Dog-Bone fillets when designing joints. These shapes create extra space in the inner corners so that the parts can fit together properly.

I first added Center Point Circles on each side of the joint holes.

Then I used the Trim tool to remove the redundant lines in the middle.

Here is the result after trimming:

Finally, I added the T-Bone/Dog-Bone features on each side of the joint holes on the left side and then mirrored them to the right side.

Note

Some of the joints may require adjustment before CNC milling.

OnShape Files (Model 1 - Table Top)

• Table Top Miniature File

• Table Top Real Size File

Model 2 - Side Table

I followed almost the same steps as in Model 1 – Top Table.

First, I created the tabletop and the table leg, and then set up the parametric design.

I used the Linear Pattern tool to duplicate the table leg into 4 pieces:

I also duplicated the tabletop into 2 pieces:

Here is the result:

Then I printed the model using a 3D printer:

Next, I adjusted the design to the real size. I scaled all of the dimensions to be 10× larger than the miniature model.

Finally, I added the T-Bone/Dog-Bone features to the joints.

Note

Some of the joints may require adjustment before CNC milling.