Coupling
From Teamnumber1
Contents |
Summary
Based on first order estimates, the working torque on the coupling was found to be 6Nm, with a drill stall torque of 80Nm. A suitable coupling, made up of two steel hubs and a nylon sleeve, and with a peak torque of 40Nm, was spec'd and ordered 9th May. (Martin)
Calculations
For our assumed worst-case work piece, with 2in diameter, and tangential cutting force of 240N, 'working torque' is approximately 6Nm. This qould be an upper bound for the torques which can be expected on the lathe.
Assuming a bell-shaped Power-Speed curve, with max drill power = 750W and max speed of 400rpm (at the lowest gear settings, again giving an upper bound), a max torque from drill was estimated as 35.7Nm. Later checks on actual drill specifications gave a max torque of 40Nm.
Assuming a linear torque-speed characteristic, and knowing torque =0 at speed 400rpm and =40Nm at 200rpm, a drill stall torque of 80Nm was estimated. This was higher than the estimated working torque by an order of magnitude (good!) and a coupling with a breaking torque of around 40-70Nm would be suitable.
Coupling Specs
Based on availibility from McMaster, the following steel-hub, nylon sleeve coupling was chosen:
- Part No's - 6247K33 & 6247K23
- Peak Torque = 347in-lbs = 39.2Nm
- Max rpm = 10,900
- Overall OD = 2.07"
- Overall Length = 2.05"
- Set Screw Size = 1/4"-20
Sketch
Martin to insert picture from notebook.
