Advantages and Applications of the Direct Connection Scheme of Servo Motor-Elastic Coupling-Lead Screw in CNC Lathes

The direct connection of a servo motor to a lead screw via a high-torque, low-inertia elastic coupling on flat-bed CNC lathes represents a core technological configuration for enhancing high-end CNC lathe performance, particularly in machining precision parts such as M12 threaded connecting rods. Below is an analysis of the core advantages of this technical scheme:

1.Revolution in Transmission Efficiency: From “Indirect Drive” to “Direct Drive” Traditional CNC lathes often adopt an indirect transmission model of “servo motor + timing belt/gearbox + lead screw.” In contrast, the direct drive scheme connects the motor to the lead screw via a high-torque, low-inertia elastic coupling, completely eliminating backlash and elastic deformation in intermediate transmission links:

Transmission efficiency exceeds 98%:Timing belt drive efficiency is approximately 90%-95%, gear drive is about 95%-98%, while the direct drive scheme has nearly no energy loss. This is particularly suitable for thread machining requiring frequent start-stop operations (such as the G76 cycle command), reducing idle travel time by 15%-20%.

Response speed increased by 30%: The low-inertia coupling allows the motor’s acceleration torque to act directly on the lead screw. The spindle accelerates from 0 to 2000 r/min in only 0.3 seconds (traditional schemes require over 0.5 seconds), making it suitable for high-speed cutting (e.g., M12 thread finishing scenarios).

2.Precision Assurance: Micron-Level Positioning and Vibration Suppression

Positioning accuracy breaks through ±0.003mm

Zero backlash transmission:The elastic coupling eliminates transmission clearance through precisely machined tooth profiles or diaphragm structures. Combined with the full-closed-loop control of the servo system (such as grating scale feedback), positioning accuracy reaches ±0.003mm, meeting the strict requirements of M12 thread pitch diameter tolerance (±0.015mm).

Thermal deformation compensation advantage: The direct drive structure reduces the number of transmission components, minimizing frictional heat generation (temperature rise is 10-15°C lower than gearbox drive). With the CNC system’s thermal deformation compensation algorithm, lead screw thermal elongation errors are controlled at a low level, suitable for long-term continuous machining.

Remarkable vibration suppression effects

Low-inertia design: The coupling’s inertia is matched with the motor rotor’s inertia to avoid resonance risks caused by “large-inertia motors driving small loads.” During M12 thread finishing, the vibration amplitude can be controlled below 1.5μm, ensuring the thread surface roughness Ra≤1.6μm.

Elastic buffering function: The coupling’s elastic elements (such as rubber or metal diaphragms) absorb high-frequency vibrations during cutting (e.g., chatter marks during thread cutting). Especially when machining difficult-to-cut materials like stainless steel, tool life can be extended by 20%-30%.

3.Rigidity and Reliability: Handling Heavy Cutting and Complex Working Conditions

High Torque Output Capability  

The servo motor directly drives the lead screw, delivering a peak torque 50% higher than timing belt transmission, which is suitable for the large cutting depth requirements during M12 thread roughing and avoids “step loss” phenomena.

Enhanced resistance to overturning moments: The direct connection structure ensures more uniform axial force on the lead screw. Combined with the pre-stretching installation process, it can withstand large radial cutting forces and reduce workpiece bending deformation.

4.Post-Maintenance: Reducing Maintenance Costs and Failure Rates  

Maintenance-Free Features Reduce Downtime Costs

Eliminating vulnerable components such as timing belts and gears extends the maintenance cycle from 3 months per time (traditional scheme) to 1 year per time, reducing annual maintenance man-hours by 20-30 hours. For enterprises with mass production, maintenance costs can be saved.

Simplified fault diagnosis: The shortened transmission chain of the direct connection structure allows the CNC system to directly determine load anomalies (such as tool wear or workpiece eccentricity) through motor current feedback, with an alarm response time of <0.1 seconds to avoid serious accidents like tool collisions.

5.Application and Machining Case  

Recently, a metal processing customer approached us with a requirement to machine M12 threaded connecting rods. After evaluation, the H32I flat-bed linear guide CNC lathe was matched to meet their machining needs.

The H32I features a flat-bed structure equipped with high-precision pre-loaded Taiwan linear rolling guides. It employs a direct connection between the servo motor and lead screw via a high-torque, low-inertia elastic coupling. The lead screw support adopts a pre-stretched structure, which eliminates transmission backlash and pre-compensates for thermal deformation errors during long-term machine operation, ensuring positioning accuracy and repeat positioning accuracy. With high positional accuracy and smooth chip evacuation, the machine is ideal for high-speed and high-precision machining.

Our engineers will work with you to match the most suitable solution.

Keywords: CNC lathe, Flat-bed CNC machine, Direct-drive CNC lathe