Adrian's Geared Extruder

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Revision as of 14:23, 21 March 2010 by Adrianbowyer (talk | contribs) (Features)
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Adrian's Geared Extruder

Release status: Experimental

Finished-rear.jpg
Description
Geared Nema17 Extruder Driver
License
GPL
Author
Contributors
Based-on
Categories
CAD Models
External Link


Introduction

Finished-front.jpg

I wanted to design a universal extruder driver that could

  1. Be bolted to the X carriage of Mendel and run as a normal extruder,
  2. Be mounted somewhere at the side and drive a Bowden extruder, and
  3. 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

  1. 55:11 gear ratio means that the motor runs on very low current
  2. No hobbing or knurling needed to make the filament driver
  3. Torque transmitted using a wing nut, giving low stress on reprapped gears
  4. Uses the same 624 bearings as the rest of RepRap Mendel
  5. 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.

Bom.jpg

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

Nozzle-assembled.jpg

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.

Wing-filing.jpg

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.

Driven-gear-assembly.jpg

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.

Driven-gear-assembly-fitting.jpg

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

Motor-filing.jpg

Drive-gear-fitting.jpg



Finished-front.jpg


Finished-rear.jpg




Here it is working

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