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7. Large format CNC (computer controlled Machining)

Objective:

The aim is to complete tasks related to Large Format CNC, which include both group and individual assignments:

Group Assignment: - Perform a test on the CNC machine to explore its basic requirements and operations. Link

Individual Assignment: - Design a component that can be assembled using press-fit techniques, with no need for additional materials, and fits within a [1220 mm x 2440 mm x 12 mm] MDF sheet. - Use the CNC machine to cut the designed parts. - Assemble the cut pieces to complete the final design.

General Information

What is CNC?

A CNC (Computer Numerical Control) machine is a machine that uses computer programming to control tools like mills, lathes, and routers. It automates processes such as cutting, drilling, and shaping materials with high precision and efficiency.

The CNC machine we use is a ShopBot, a large-format machine designed for precise cutting of materials such as wood. It utilizes a range of spindle cutting tools in various sizes and is controlled by a computer that receives commands based on designs created in CAD software. The machine follows toolpaths to guide the cutting tool, adjusting parameters like spindle speed, feed rate, and cutting depth to ensure accurate and efficient results.

Safety Requirements:

  1. Personal Protective Equipment (PPE): Always wear safety goggles, safety shoes, and ear protection to protect yourself from flying debris and noise. Ensure long sleeves are rolled up or wear a lab coat without loose clothing that could get caught in the machine.

  2. Machine Inspection: Before operation, check the machine for any visible issues, ensure all parts are secure, and verify that the cutting tool is properly installed.

  3. Emergency Stop: Familiarize yourself with the location and operation of the emergency stop button in case of an emergency.

  4. Clear Work Area: Keep the work area clean and free of obstructions. Ensure no one is standing too close to the machine while it is in operation.

  5. Proper Setup: Make sure the material is properly secured to the machine bed before starting the cutting process.

  1. Supervision: Never operate the machine without proper training and, if needed, supervision.

  2. Dust and Debris Control: Ensure that dust collection systems are properly set up and functioning to minimize airborne particles.

  3. No Distractions: Avoid distractions and always stay focused while the machine is in operation.

  4. Power Down After Use: Always turn off the machine and disconnect power when maintenance or adjustments are required.

CNC Operation Guidelines and Key Considerations:

– Material Alignment and Sacrificial Sheet: Proper material alignment on the CNC bed is essential for accurate cuts. A sacrificial sheet is placed beneath the material to protect the machine bed and ensure clean cutting. Additionally, the sacrificial sheet helps secure the material by screwing it down, preventing any bending during the cutting process.

– Debris Management: The CNC machine is equipped with a vacuum system that effectively removes debris created during the cutting process. This is essential for maintaining a clean work environment and ensuring precise, accurate cuts.

– Importance of Dogbones: When designing joints, it’s crucial to include dogbones. These adjustments allow the square corners of the design to fit together properly, accommodating the round cutting tool for a seamless joint fit.

Group Assignment:

For the group assignment, my responsibility was to gather information on the safety measures required for operating the machine, as well as the machine specifications.

Group Assignment Link During the group assignment, I gained valuable knowledge about operating the CNC machine, focusing on the following key aspects:

  1. Safety Precautions: Ensuring proper safety measures before operating the machine, such as wearing safety goggles, safety shoes, and avoiding loose sleeves or lab coats.
  2. Machine Start-Up: Understanding the correct procedure to start the machine.
  3. Axis Management: Learning how to manage the X and Y axes and zero the Z-axis to ensure accurate cutting.
  4. Speed and Feed Rate: Setting the appropriate speed and feed rate for the milling bit.
  5. Tool Path Adjustment: Adjusting whether the tool should cut along the line, inside the line, or outside the line.
  6. Dust Cover Management: Knowing how to install and remove the dust cover correctly.
  7. Bit Change: Understanding how to change the machine bit effectively.
  8. MDF Setup: Learning the proper method for setting up the MDF sheet on the machine for the machining process.
  9. Cutting or Engraving: Specifying whether the machine will cut or engrave the lines.

Individual Assignment:

Results

Download table STL file

Download table DXF file

We were tasked with designing a large-scale project using the CNC machine and an MDF wood sheet. The design needed to follow these guidelines and constraints:

↪Design Guidelines and Constraints

  1. Press-Fit Assembly: The design must be created using press-fit techniques and wood joints for assembly. Mechanical fasteners are not allowed.
  2. Size Requirements: The product must be large, with at least one dimension measuring 90 cm or more.
  3. Material Limitations: The design must fit within a single MDF sheet with the dimensions of 2440 mm (length) x 1220 mm (width) x 12 mm (thickness).

↪Design Process: Designing with Fusion 360

Step 01:
Using Fusion 360, I designed a press-fit wooden table with curvilinear legs to be cut on the CNC machine. Below are the steps I followed:

  1. I started by selecting “Create Sketch” and then choosing the rectangle tool from the toolbar.

  2. I drew the main shape of the table legs, creating a rectangle with dimensions of 900mm x 500mm.

  3. Next, I offset the sides of the rectangle by 50mm to ensure the legs were uniform in size. This step also formed the basic guidelines for the curvilinear legs I aimed to design.

Step 02:
After completing the rectangle, I pressed the (L) keyboard shortcut to create an inclined line for the legs, starting from the top offset point and meeting the bottom original rectangle point. Once the line was created, I used the (T) keyboard shortcut to activate the “Trim” tool, removing unnecessary lines and resulting in a trapezoidal shape for the legs.

Step 03:
Once the trapezoidal shape was created, I selected Fit Point Spline from the “Create” menu to begin forming the upper and bottom curves of the legs. I used the previously created offset line to ensure the bottom leg surface remained 50mm in length for stability. To refine the shape, I used the (T) keyboard shortcut to activate the “Trim” tool and removed any excess sketch lines, achieving the final leg design.

Step 04:
After completing the leg outline, I duplicated it to create the second leg and the connection points. I added a rectangle over the design and drew lines to the center to ensure everything was aligned. This would help in creating the central connection points. Then, I used the (O) keyboard shortcut to activate the “Offset” tool. In the Offset panel, I selected the Two Sides option and set the offset value to 12mm, matching the thickness of the MDF wood.

Step 05:
Next, I trimmed the extra lines using the (T) keyboard shortcut to activate the “Trim” tool. I also added dimension lines to make the design parametric.

Step 06:
To make the design parametric, I went to the Modify Panel and selected the Change Parameters option. I added the name of one of the measured lines, d55, in the expression of line 56, which linked the dimension to the first line. Any change in the dimension of d55 would automatically adjust line 56. After pressing OK, a parametric function was added (fx: 12.00).

Step 07:
Once the parameters were set, I clicked on Finish Sketch. Using the (E) keyboard shortcut to activate the “Extrude” tool, I extruded the legs by 12mm, matching the thickness of the MDF wood sheet. I then used the (M) keyboard shortcut to activate the “MOVE/COPY” tool, rotating one of the legs by 90 degrees. To align the legs in the center, I used the Align feature from the Modify Panel.

Step 08:
After placing the legs, I started creating the press-fit joints on top of the legs. I selected the top connection point and used the (E) keyboard shortcut to extrude the joint, setting the extrude value to 12mm, similar to the thickness of the MDF wood.

Step 09:
After completing the table legs, I started designing the top surface of the table. I clicked on Create Sketch, then added a guideline from the center of the intersection of the legs to the end of one of the legs. From the Create dropdown panel, I selected Center Rectangle and drew a square using the guideline, with dimensions of 900mm x 900mm. Once finished, I pressed Finish Sketch.

Step 10:
After completing the sketch, I extruded the table top by selecting it and using the (E) keyboard shortcut to activate the “Extrude” tool. I extruded the top by 12mm, matching the thickness of the MDF wood sheet. Then, I selected the 4 corners of the square and applied a fillet with a radius of 450mm, transforming the square into a circular shape.

Step 11:
Once the table top was transformed into a circular shape, I began creating the press-fit cuts for the connection points. Using the (E) keyboard shortcut to activate the “Extrude” tool, I created Extrude Cuts for the connection areas. After the cuts were made, I extruded the connection. Finally, I aligned the table top with the legs using the Align feature from the Modify Panel, completing the final design of the table.

Final Table Design

↪Saving the File as DXF:

  1. I moved and rotated the table parts to ensure they lie flat on the same surface (e.g., the XY plane).

  2. I created a new sketch layer by selecting one surface, then pressed P to create a project and selected the other surfaces. Afterward, I pressed Enter to create a new sketch.

  3. I saved the sketch as a DXF file by right-clicking on the new sketch and selecting Save as DXF.

↪Using VCarve to CNC Cut the Table Design:

  1. Import the design file as a .DXF file into the software.

  1. Create a rectangle with a 20mm offset to ensure the cutting stays away from the MDF secure nails added for holding the material.

  1. Apply a Dog-Bone Fillet to the joints that require it to ensure proper fitting.

  1. Change the Passes value to 3, meaning the CNC machine will pass over each piece three times to fully cut through.

  1. Add tabs to the design to secure the pieces in place while being cut.

  1. A pop-up Material Warning will appear, stating that the machine will cut through the material, as we set the cut depth to 13mm (greater than the MDF thickness of 12mm).

  1. Select the machine path to define the cutting process.

↪Setup the CNC Machine for Printing:

  1. Before starting, ensure you have followed all the necessary safety instructions.

  2. place the wood board on the CNC machine and secure its corners with screws to prevent movement.

  3. Using the machine’s keypad software, set the X and Y coordinates to 0. sheet attached to the machine.

Then, fix the Z-axis position using the metal.

  1. Press and hold the green start button for 3 seconds to begin the printing process.

Warning: While printing, avoid pressing anything on the computer screen as this will interrupt the printing process.

↪Cutting Process:

The CNC machine began cutting the table design, as shown below.

Once the cutting was complete, our instructor began removing the pieces using the tip of a steel file, as shown in the image below.

↪Filing Process:

After the pieces were removed, we needed to sand the tap positions where prominences had formed on the edges. I used a file to smooth out the excess material, ensuring a clean finish.

↪Assembly Process:

Once the sanding was complete, my classmate Ammar, our instructor Faisal, and I began assembling the table. We placed the table surface on the ground and used a hammer to secure the legs in place, ensuring a solid and stable structure.

Last update: January 27, 2025