A Nema14 compact dual drive geared extruder

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A Nema14 Compact Dual Drive Geared Extruder

Release status: experimental

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Description
A dual drive geared extruder made with a Nema14 motor.
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Introduction

In an earlier post [1] I described a dual drive geared extruder made entirely from scratch and explained why this design could be better than others projects of geared extruders. With ABS and hot end set to 220C and a 0.4 mm nozzle the extruder yielded a flow rate of 25 mm3/s, a good result. But the overall assembly was bulky (but no problem if its used as a Bowden extruder). In this post I describe a more compact version of a Dual Drive Geared Extruder, made with a Nema14 motor. The motor/drives transmission rate was 69:15. The motor used (Applied Motion model 5014-819) was saved from an old table scanner. Each motor coil have a resistance of 3.8 Ohms and a recommended motor current of 0.5 A. A A4988 driver from the RAMPS1.4 shield can easily run such a motor, but as the motor size and current were small, I wondered if I could obtain a reasonable flow rate. To my surprise, I could obtain a flow rate of almost 25 mm3/s, similar to the former development shown in [2]. At the end of this post is a video that shows a test of the extruder. It was possible to get a 1.75mm filament feed rates of almost 10 mm/s (or flow rate of almost 25 mm3/s) without slipping or motor stalling.



Overview

The stepper motor and gears used in this project were saved form old laser printers and table scanners. The other parts were made with aluminium scraps using a lathe and a milling machine or 3D printed in PLA. I had in my scrap gears box three modulo 0.5 gears: a smaller one with 15 teeth and two larger, with 69 teeth each. The shaft of a Nema14 stepper motor is attached to the 15 teeth gear. This gear is coupled to a 69 teeth gear connected to the first hobbed drive. The rotation is reversed by another 69 teeth gear that is connected to the second hobbed driver. Therefore, the motor/drivers transmission speed ratio was 4.6:1. In this design the filament is pressed in opposite sides by bearings supported by a lever, as shown in the figure bellow. The MK8 hobbed gears were made from scratch as well [3].


Geared dual drive


The main advantages of this design are:

The gears distance does not vary. They are tightly coupled to have minimum backlash.
The filament is griped in two opposite sides.
Radial force on motor shaft is minimized.

The mounting sequence of the extruder is shown in sections ahead. All CAD files, images and STEP files can be downloaded from: [4].


Mounting sequence

The rear plate of the extruder was machined in Aluminium. The first steps consist on attaching the Nema 14 motor and inserting the bearings for the gears' axis. Attaching the motor to an aluminium plate is useful to act as a heat sink for the motor. Some attempts to 3d print the back plate in PLA did not worked: trying to overdrive the motor's current to increase the flow rate heated the motor to a temperature high enough to melt the PLA backplate.

Figure 1 - Back Plate Mounting.
Figure 2 - Back Plate Ready.
Figure 3 - Insert 69 Teeth Gears.



The next two figures show the mounting of the PLA front plate. The bearings for the gears' axis are inserted and should match tightly in their holes. At the bottom is attached an aluminium bracket to support the hot end.

Figure 4 - Front Plate Mounting.
Figure 5 - Front Plate Ready.