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- 1 MOST Planetary Gearbox and MOST Geared Extruder Drive
- 2 Bill of Materials
- 3 Assembly
MOST Planetary Gearbox and MOST Geared Extruder Drive
A planetary gearbox (more appropriately, https://en.wikipedia.org/wiki/Planetary_gearbox Epicyclic gearing) is a compact and efficient transmission. The MOST planetary gearbox is used in a number of applications in the MOST 3-D printer research program.
This assembly guide actually covers the complete assembly of the MOST Geared Extruder Drive, which is derived from http://airtripper.com/1071/airtrippers-bowden-extruder-v3-updated-design/ Airtripper's Bowden Extruder. Assembly of the gearbox is essentially unaffected by the geometries of the motor and output ends, in this case a vertical mount motor end and a MOST extruder block output.
Extruder drive capabilities
Airtripper's Bowden Extruder is a great platform that has been improved upon:
- The drive body has been placed atop a 4.62:1 planetary gearbox, eliminating torque issues.
- The filament path has been straightened so there is little to no bending around the gear, reducing power requirements and making possible live swapping of filament.
- Gaps between the drive gear and filament openings have been reduced helping to minimize jamming.
- The OpenSCAD design has been parameterized allowing for easy manipulation of the design and permitting one line switching between 1.75mm and 3mm filament drives.
- An infeed tube has been added to facilitate live swapping of filament. Even very short pieces of filament can be introduced with very few jams.
Bill of Materials
Common to all MOST planetary gearboxes
- Motor end (1)
- Output end (1)
- Planetary carrier (1)
- Sun gear (1)
- Planet gear (3)
- Input half annulus gear (1)
- Output half annulus gear (1)
- 624zz ball bearing (3)
- M3 x 12mm or 14mm socket head cap screw (4; different screw dimensions required for different motors)
- M3 x 30mm socket head cap screw (typically 3, can vary with number of case screws used in design)
- M3 x 8mm cup point set screw (1)
- M3 flat washer (typically 6, varies with case screw count)
- M3 nut (typically 4, varies with case screw count; one required for sun gear)
- M4 x 16mm socket head cap screw (3)
- M4 flat washer (9)
- M4 nylock nut (3)
- NEMA stepper motor with d-profile shaft (typically NEMA17, can vary with design)
- Output shaft (hex head cap screw with dimensions varying by design)
- Output ball bearing (varies with output shaft)
MOST geared extruder drive
- Extruder block output end (1)
- Idler housing (1)
- Idler shaft (1)
- Idler pivot linking rod (1)
- 608zz ball bearing (1)
- MR105zz miniature ball bearing (1)
- Mk7 drive gear (1)
- M5 x 30mm hex head cap screw (1; output shaft)
- 625zz ball bearing (1; output bearing)
- 1/4" reinforced rubber fuel line, 1" long (1)
- M3 x 30mm socket head cap screw (2)
- M3 x 40mm or 45mm socket head cap screw (2)
- M3 flat washer (2)
- M3 nut (4)
- (NEMA 17 stepper motor wit D-profile shaft)
- Place a 624zz ball bearing in the recess provided in each of the three planetary gears.
- Pass the M4 x 16mm screws through the bearing with the head of the screw on the same side as the bearing recess. Do not put a washer between the screws' heads and bearings.
- Press the three M4 nylock nuts into the nut traps in the planetary carrier.
- Place three M4 flat washers on the ends of the M4 screw in the planetary gears and thread loosely into the nylock nuts in the planetary carrier.
- Press an M3 nut into the sun gear's set screw nut trap and start the M3 x 8mm cup point set screw into the nut with the cup end facing towards the motor shaft recess. Do not thread the set screw into the recess.
- Tighten the M4 screws, securing the planetary gears firmly to the planetary carrier. Ensure that the the sun gear freely engages and rotates the planetary gears.
- Remove protuberances from the gear teeth in the annulus halves with a sharp knife.
- Prepare the output end; clean with a sharp knife and ream out holes, especially the output shaft hole. Press in those nuts required for mounting components to the output end. For the geared extruder drive shown:
- Ream the filament path with the appropriately sized drill bit (2mm for 1.75mm filament, 3mm for 3mm filament).
- Press in two M3 nuts in the locations where the M3 x 30mm screws secure the idler pivot linking rod.
- Set the MR105zz ball bearing on top of the drive gear.
- Place the output bearing on the output shaft. The output bearing for the extruder drive shown is a 625zz bearing.
- Align the sun gear such that the set screw is facing the set screw access port on the motor end and press the assembly onto the motor.
- Tighten the sun gear's set screw, which should be visible through the set screw access port in the motor end.
- Lubricate the gearbox with spray-on white lithium grease, placing the hose from the bottle into the set screw access port. Lubricant will leak from the gearbox an diffuse through the porous prints - be prepared to catch drips!
- Exercise the gearbox by providing power to the motor and making several rotations - the longer the better. Rotation can be helped along by placing jammed nuts on the output shaft and using a wrench when the gearbox jams. Do not apply too much force, they are, afterall, just plastic gears.
- After exercising the gearbox, tighten the case screws and check that the gearbox still rotates.
Continued assembly of the geared extruder drive
- Snap or cut off the base on the idler shaft. Cut off all remaining protuberances from the shaft.
- Slide the shaft through the 608zz bearing.
- Press the shaft and bearing into the idler housing.
- Pass a short length of the appropriate filament through the entire filament path. Move the Mk7 drive gear such that the filament engages it in the center of the hobbed portion of the drive gear. Tighten the drive gear's set screw when it is in the proper position.
- Pass the M3 x 30mm socket head cap screws through the holes in the linking rod with the screw heads sitting fully in the recesses provided.
- Attach the idler pivot linking rod to the extruder block. Tighten the screws.
- Attach the idler assembly to the pivot screw and engage the preloader.
- Prepare Bowden tube sheath by plastiforming threads into the PTFE tubing (detailed http://www.appropedia.org/Assembling_Delta_Effector:MOST here).
- Thread the appropriate sheath retainer (M4 nut for 1.75mm filament, M6 nut for 3mm filament) onto the end of the Bowden sheath and pres the nut into the slot on the preloader side of the extruder block.
- Prepare a short infeed tube similar to the Bowden sheath, with only one threaded end, and slide the nut into the slot on the opposite side of the extruder block.