Adrian's Geared Extruder
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Release status: Experimental
Description | Geared Nema17 Extruder Driver
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License | GPL
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Author | |
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Contents
Introduction
I wanted to design a universal extruder driver that could
- Be bolted to the X carriage of Mendel and run as a normal extruder,
- Be mounted somewhere at the side and drive a Bowden extruder, and
- Be mounted somewhere at the side and drive a Bowden paste extruder, as outlined here.
This is my first hack at a solution.
This design was inspired by Wade's neat geared extruder that you can find here.
Features
- 55:11 gear ratio means that the motor runs on very low current
- No hobbing or knurling needed to make the filament driver
- Torque transmitted using a wing nut, giving low stress on reprapped gears
- Uses the same 624 bearings as the rest of RepRap Mendel
- Designed to work at higher extrude speeds than the standard Mendel extruder, giving shorter build times.
What you need
This describes what you need to build an extruder to mount on Mendel. The Bowden variations will be added below when they have been tested.
The design files (AoI, STLs, and the complete RFO for immediate reprapping) are in the repository here.
This picture shows all the parts (some partly assembled) except for the two M4x20 screws that attach the extruder to Mendel's X carriage.
Description | Quantity |
M3x10 | 4 |
M4x12 | 2 |
M4x20 | 2 |
M4x45 | 6 |
M4x55 | 2 |
M4 nuts | 13 |
M4 wing nut | 1 |
M4 washers | 21 |
624 bearings | 3 |
NEMA17 stepper | 1 |
M4 threaded rod | 70mm |
4mm diameter rod | 25mm |
M4 insert | 1 |
Strip-board | 50mmx25mm |
4-way pin headers | 2 |
4-way ribbon cable | 130mm |
16mm dia PTFE | 50mm |
M6 threaded brass | 36mm |
Thermistor | 1 |
Kapton tape | 200mm |
Nichrome wire | 6 ohms |
Araldite rapid | About 5 ml |
Here is a complete list of all the non-reprapped parts and materials.
The M4 Insert is the heart of the device. It is available from here. It has an internal M4 thread and a locking grub screw. This means that it is very easy to mount on the 70mm length of M4 threaded rod, but that - once it is tightened up - it never slips.
Putting it together
The nozzle
Start by building the extruder nozzle. This is exactly the same as the one on the standard Mendel extruder here except that the PTFE is longer at 50mm than the 35mm used for the standard design. I also cut the M6 thread slightly longer (18 mm) than the 15mm used for the standard design, and made a correspondingly longer brass nozzle.
The reasons for these changes (which may not actually be necessary) were conservative: I wanted to be really sure that the Araldite join between the PTFE and the base of the device would stay very cool and so not soften. And I wanted to make sure that the brass nozzle would not break lose, even under higher forces than the original extruder is capable of generating. One of the main reasons for designing this device - as mentioned above - is to increase the speed of extrusion. Doing that will obviously generate higher thermal and mechanical stresses, and so I thought it best to be prepared.
The gear drive
The large 55-tooth gear is the one that drives the filament. It connects to the 70mm M4 threaded rod using a wing nut, which spreads the torque load on it and thus reduces the stress that the plastic is subjected to.
Start by offering up the wing nut to the slots in the large gear on the opposite side to the projecting boss. Some wing nuts fit immediately. Unfortunately there does not seem to be a completely standard shape for wing nuts, so you may have to file down the inner shoulders of yours to fit, as shown here.
This shows the assembled filament drive. The sequence from the bottom is:
M4 nut | M4 washer | 624 bearing | M4 washer | M4 Insert | M4 washer | 624 bearing | M4 washer | M4 nut | GAP | M4 nut | M4 wing nut | gear | M4 washer | M4 nut |
There are a couple of extra washers in the picture between the wing nut and the nut that locks it - these are not needed. The final M4 washer and nut are invisible behind the gear.
Get everything in the right sequence and hand-tighten it all. Don't use spanners and force yet.
This shows the assembly fitted in its slots in the extruder. Use a short length of filament down through the device to hold it in place while you build the rest.
The stepper drive
Here it is working
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