8. Computer-Controlled Machining

Group Assignment Requirements:

The group assignment for this week is the following:

• Complete your lab’s safety training
• Test runout, alignment, fixturing, speeds, feeds, materials and toolpaths for your machine
• Document your work to the group work page and reflect on your individual page what you learned

Large format CNC router machine specs:

Machine name: Shopbot Spindle max speed in RPM: 16,500 Machine bed size (work area): 1220mm x 2400mm Toolpath generation software used: VCarve

Safety

Saftey rules for working in the lab:

1. Eye Protection: Always wear appropriate eye protection when operating the CNC router machine.

2. Ear Protection: Use ear protection to safeguard against the noise generated by the machine during operation.

3. Avoid Accessories: Refrain from wearing accessories such as watches, rings, or bracelets while working with the machine to prevent entanglement hazards.

4. Avoid Loose Clothing: Do not wear oversized or dangling clothes, such as scarves, as they can get caught in the machine’s moving parts.

5. Wear Closed Footwear: Ensure to wear closed proper footwear to protect your feet from any potential hazards in the workshop environment.

Additional Safety Considerations

• Dust Collection System: A proper duct collection system is in place to minimize airborne dust generated during machining processes, ensuring a cleaner and safer working environment.

• Safety Posters: Safety-related posters are prominently placed near the machine to remind users of important safety protocols and procedures.

• Emergency Stop (E-stop) Buttons: Multiple emergency stop (E-stop) buttons are strategically located around the workshop, providing quick and easy access to shut down the machine in case of an emergency, enhancing overall safety measures.

Materials

At the lab, we use the machine to cut a variety of materials including MDF, plywood, blockboard, acrylic, foam, and others. For this assignment, our primary focus was on testing 18mm plywood and 18mm blockboard.

Fixturing and Machine Setup

Fixturing:

For fixturing, we use screws to secure the material to the bed of the machine. The process involves attaching the screws along the borders of the stock piece.

Here’s a step-by-step guide to our fixturing process:

1. Drill Pilot Holes: First, we drill pilot holes into the material along its borders. These pilot holes serve as guides for the screws and help prevent the material from splitting.

2. Attach Screws: Using a cordless drill, we attach screws into the pilot holes. The screws firmly hold the material in place during machining operations.

This method ensures a secure hold while minimizing the risk of material damage. It also allows for efficient setup and removal of the material for successive machining tasks.

But for smaller pieces we use a vice atatched to the bed with screws to provide a versatile and secure method of fixation, enabling precise machining while ensuring stability and safety.

After making sure the material is securely in place, we continue the machine setup process.

Machine Setup

After securely fixing the material onto the machine, we proceed with the setup process, which involves replacing the bit and zeroing the axis, ensuring precise machining operations.

Replacing the Bit:

1. Use of Wrenches: We utilize a combination of a regular wrench and a collet wrench to carefully remove the collet nut from the spindle. The collet wrench provides a secure grip on the collet while the regular wrench is used to unscrew the collet nut.

1. Careful Removal: Once the collet nut is loosened, we carefully remove the bit, collet, and collet nut from the spindle, ensuring delicate handling to prevent any damage to the components.

1. Collet Inspection: If needed, we inspect the collet to ensure compatibility with the new bit. If necessary, we replace the collet to match the size of the bit that will be used for machining.

2. Cleaning Surfaces: Before reassembly, we meticulously clean all surfaces of the collet, collet nut, and spindle to remove any debris or residue. This ensures proper alignment and tightening during reassembly.

1. Reassembly: We attach the collet to the collet nut and screw it by hand onto the spindle. Once secured, we insert the new bit into the collet and tighten it securely using the collet wrench and regular wrench.

Zeroing the Axis:

1. Using ShopBot Control Software: We utilize the ShopBot control software to manipulate the spindle’s movement. Using the keyboard controls, we move the spindle to the corner of our material.

1. Zeroing X and Y Axes: From the software interface, we zero the X and Y axes, ensuring that the spindle is precisely aligned with the material’s corner.

2. Zeroing Z Axis: To zero the Z axis, we move the spindle close to the surface of the material. We then switch the movement mode to fixed, allowing for precise adjustments without the risk of collision with the material. Using a piece of paper, we measure the clearance between the bit and the material surface. By moving the paper back and forth while simultaneously lowering the Z axis, we ensure that the paper is snug and won’t move. Once the paper is snug, indicating the desired clearance, we zero the Z axis. This ensures that the spindle is accurately positioned at the surface of the material, ready for precise machining operations.

Toolpath Generation Using VCarve

In VCarve, the toolpath generation process involves several steps to prepare and create toolpaths for machining operations.

1. Set Job Dimensions:

2. Start by defining the dimensions of the job or workpiece in VCarve, specifying the length, width, and thickness of the material.

3. Create Geometry:

4. Place a square shape representing the outline of the desired cut on the material. This square serves as the basis for creating multiple squares using the array tool.

5. Array Tool:

6. Utilize the array tool in VCarve to duplicate the square geometry and create an array of six squares, ensuring uniform spacing and alignment between each square.

7. Profile Toolpath Creation:

8. Generate a profile toolpath for cutting the squares out of the material. This toolpath defines the tool’s path and depth of cut to achieve the desired shape.

9. Toolpath Settings Adjustment:

10. Adjust the settings of the profile toolpath according to the specific requirements of the machining operation. This includes selecting the appropriate tool, specifying feeds and speeds, and choosing between conventional and climb milling techniques.

11. Additionally, options such as adding a ramp to the toolpath for smoother entry and exit, as well as adding tabs to prevent the cutout pieces from moving during machining, can be configured as needed.

12. Machine Vectors:

13. Choose the machine vectors option to determine whether the tool will cut outside, inside, or on the line of the designated geometry. This ensures precise cutting according to the intended design.

14. Start Depth and Cut Depth:

15. Specify the start depth and cut depth parameters for the toolpath, indicating where the cutting operation should begin and how deep it should go into the material.

16. Toolpath Saving and Exporting:

17. Once all settings are adjusted, save and export the toolpath for each square individually, ensuring that the feeds and speeds are tailored to the specific requirements of each square. This allows for customization and optimization of cutting parameters for different sections of the material.

By following these steps in VCarve, users can efficiently generate toolpaths for machining operations, ensuring accuracy and precision in cutting multiple squares with varying feeds and speeds.

Speeds and Feeds

To calculate the optimal speed and feed for machining blockboard using a 6mm straight 3-flute endmill, we utilized an online tool, specifically fswizard.com. Here’s how the process unfolded:

1. Accessing the Online Tool: We accessed the fswizard.com website, which provides a comprehensive platform for calculating speeds and feeds based on various parameters such as material type, tool geometry, and cutting conditions.

2. Input Parameters: We input the relevant parameters into the online tool, including the material type (wood), tool type (6mm straight 3-flute endmill), and desired cutting depth (6mm for engraving).

3. Calculation: The online tool then processed the input parameters and calculated the recommended spindle speed and feed rate for optimal machining performance. After the calculation, the tool provided us with a recommended spindle speed of 15500 RPM and a feed rate of 2800 mm/min.

Testing and Adjustment

Following the calculation of the optimal speeds and feeds, we proceeded to conduct practical tests to verify the effectiveness of the recommended parameters. Here’s how the testing process unfolded:

1. Exceeding Recommended Spindle Speed: We tested the machining process by increasing the spindle speed by 1000 RPM above the recommended value of 15500 RPM. This allowed us to assess the machine’s performance at higher speeds and determine if any improvements in cutting efficiency were observed.

2. Reducing Spindle Speed: Conversely, we also conducted tests by reducing the spindle speed by 3000 RPM below the recommended value. This enabled us to evaluate the impact of slower speeds on machining quality and efficiency.

3. Adjusting Feed Rate: Additionally, we adjusted the feed rate from the recommended 2800 mm/min to 1800 mm/min to assess the effect of a lower feed rate on cutting performance and surface finish.

Engraving Process

During the testing phase, we focused on engraving blockboard to a depth of 6mm using the 6mm straight 3-flute endmill. This process allowed us to evaluate the suitability of the selected speeds and feeds for engraving applications and determine the optimal combination for achieving the desired engraving depth with precision and efficiency.

By completing this test, we found that for cengraving blockboard, with a depth of 6mm, using a 6mm bit, the best settings are the following:

Feed rate: 2800mm/min Spindle speed: 15500rpm Plunge rate: 500mm/min Pass depth: 3mm

Runout & Alignment

Runout refers to the deviation of the tool or spindle from its intended circular rotation, which can lead to inaccuracies in machining. To assess runout, we utilized a dial test indicator to measure any deviations from the true circular rotation.

Axis alignment is crucial to ensure that the machine’s axes (X, Y, and Z) are properly aligned and parallel with each other. Misalignment can result in poor surface finish and inaccuracies in machined parts.

To evaluate the runout and alignment of our CNC router machine, we conducted a test by cutting a square with dimensions of 35cm by 35cm. The results of our measurements showed consistent dimensions across multiple areas of the square, with a negligible difference of 0.2mm.

This result indicates excellent alignment and minimal runout, ensuring precise and accurate machining. Overall, the outcome confirms that our CNC router machine is well-calibrated and capable of producing high-quality machined parts.