This follow-up video details the engineering and design process behind the two-stage belt drive system for a custom tool post milling spindle. The creator outlines the ambitious RPM range requirements (50 RPM to 30,000 RPM) and various practical constraints, including material size limitations, belt specifications, and the need for a compact design. The iterative design methodology is highlighted, showcasing the use of Excel spreadsheets for calculating pulley diameters and CAD software for visualizing belt paths and developing the unique slot for the tensioning mechanism. Despite the low-end torque demonstrated by the servo motor, an M12 power tapping attempt fails due to belt slippage. The video concludes with a preview of future high-speed testing, which will require pre-warming the spindle bearings.
Designing the Dual-Stage Pulley Drive for a High-Performance Milling Spindle
0:00 Project Context: This video serves as a follow-up, delving into the design of the two-stage pulley drive system for a new lathe's tool post milling spindle.
0:21 Post-Project Cleanup: The creator starts by showing the extensive aluminum and steel chips accumulated on the lathe after the spindle project, emphasizing the necessary cleanup.
1:00 Ambitious RPM Range: The primary design goal was an extremely wide RPM range for the spindle, from a slow 50 RPM for power tapping to a high 30,000 RPM for internal grinding with small tools.
1:38 Low RPM Torque: The servo motor demonstrates impressive torque even at the slowest setting (50 RPM spindle, 200 RPM motor), making it difficult to stop by hand.
2:04 Design Constraints: Numerous limitations influenced the design, including:
2:04 Material Availability: Max stock diameter of 62mm, and a tight deadline forcing the use of existing materials.
2:32 Pulley Sizing: Restrictions on the smallest (due to keyway intersection) and largest (to avoid interference with spindle housing) spindle pulley diameters.
3:10 Single-Stage Infeasibility: A single-stage belt drive was impractical due to the massive motor pulley (approx. 130mm) required for the 30,000 RPM.
3:39 Belt Limitations: Poly-V (PJ profile) belts constrained the smallest possible pulley diameter (around 20mm) due to their minimum bend radius.
4:09 Intermediate RPMs: A requirement for a functional intermediate speed range (2,000-15,000 RPM) for general machining tasks.
4:30 Tool-Free Belt Change: A desired feature to allow easy and quick belt changes.
4:37 Three Pulley Diameters: The chosen design incorporates three different pulley diameters for each of the motor, idler, and spindle pulleys, providing six distinct speed settings.
4:54 Design Tools & Iteration: The creator developed an Excel tool to simulate RPM ranges based on different pulley diameters and used CAD software to visualize belt spacing and design the precise slot for the idler pulley's tensioning mechanism.
8:11 Mechanical Considerations: Challenges included ensuring sufficient material for bearing installation and keyway reliefs, especially in thinner pulley sections, and preventing tool chatter when cutting V-grooves.
12:44 Design Oversights & Iterations: A minor design flaw was noted where the lid collides during closing (only checked in closed position). Multiple 3D-printed prototypes were made for various components like the motor mounting plate, hinges, and lid.
13:17 Power Tapping Attempt: An M12 power tapping test failed at 50 RPM due to the belt slipping, indicating the drive system couldn't transmit enough torque for this specific operation, suggesting it might work for smaller taps (M10 or M8).
15:19 Future High-Speed Testing: Achieving the 30,000 RPM maximum speed requires pre-warming the spindle bearings for 10-20 minutes at a lower speed (10-15,000 RPM) to warm the grease, which will be featured in a subsequent main channel video focusing on grinding.