Lyman Filament Maker Calculations
Torque
- The filament extruder motor of the Lyman Filament Maker has a 168 fold geardown. It has a 173 kg-cm (1730 N cm) torque! [1]
- 3000 N cm torque stepper - $60 - [2]. That is about 300 kg cm.
Stepper has over 2x performance to cost ratio
The torque of the Precious Plastic shredder is recommended at 70 rpm with a 1/4 hp or higher motor. Using the Motor Torque Calculator, that comes out to 2800 N cm. The stepper motor above meets this specification (for torque, but not speed).
The Recyclebot motor (the stepper) has 15 geardown. Say steppers go up to 1000 RPM - that is exactly about 70 RPM if there is a 15 fold geardown.
Take a regular Nema 17 with 72 oz in torque. That is about 5 kg cm. To get to 300 kg cm - need about 60 geardown.
As a first try, it is useful to go with the 15 geardown stepper above for an initial version of the shredder.
High Torque 3D Printed Couplers
Hex shaft used in the Precious Plastic Shredder is a good idea. We can make a heavy duty plastic coupler as a plastic/metal composite structure:
- 3D print a 100% infill Hex Coupler with 1.5" walls, and about 4" long
- Embed 6 nut catchers, either 3/4" or 1/2" into the coupler to strengthen the hex-on-shaft force handling ability.
- Clamp down with bolts through the nut catcher to hold the shaft firmly in place
If 5000 PSI is the Tensile Strength of Plastic, ABS or PLA plastic, we can get to about 4,000 in lb (500 Nm, 50,000 Ncm) (or about 500 kg force at the 4" radius of shredder teeth) with a safety factor of about 10 using the plastic metal composite:
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