Wade's Geared Extruder

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Wade's Geared Extruder

Release status: Working

GearedNema17.jpg
Description Geared Nema 17 Extruder
License GPL
Author Wade
Based-on Mendel
Categories Extruders Cold End
CAD Models File:M8 Extruder 3.zip

File:M8 Gears.zip

External Link Thingiverse

This work is based on Adrian's Geared Nema 14 extruder (Adrian's Geared Extruder) design, and includes many concepts lifted from Nophead's extruder (Nophead's Extruder Tweaks) research.

This extruder was designed for the RepRap Sells Mendel (but will work with about any 3D printer, if with adaptors) and is robust, provides a strong force to extrude, is cheap and DIY. It is an alternative to the Geared Nema17 Extruder Driver and has the following advantages:

  • no need to buy/use expensive metal gears;
  • no need to do two precision flats on motor shaft;
  • no need to glue the PTFE barrel;

Other advantages over other extruders are:

  • extrude/print at high speed;
  • good for use with a low torque/cheap Nema 17 motor ; (Needs verification)
  • no need to use expensive and complex tools - just one hand drill, a file and a M4 or M5 tap;
  • no need to make splines on motor shaft;

Contents

How to get it

While this design is made with DIYers in mind, if you can't make your own, or simply don't want to, you can always buy one. There are users printing it and selling on Ebay.

Mechanical Construction

Materials

Printed Parts

Quantity Description Type Comments Diagram
1 extruder block RP File:M8 Extruder 3.zip M8-extruder-block-3.jpg
1 extruder idler block RP File:M8 Extruder 3.zip M8-extruder-idler-block-2.jpg
1 11 tooth drive gear RP File:M8 Gears.zip 11t17p.jpg
1 39 tooth M8 hub driven gear RP File:M8 Gears.zip 39t17p.jpg

Non-Printed Parts

Quantity Description Type Comments
Feeder
2 608 bearings, skateboard bearings Bearings
1 M8×50 bolt Fastener to be hobbed, M8×60 has a longer smooth part, allows a second lock-nut, and may be easier to find
1 M8 nut Fastener Nyloc works better, but a pair of nuts will also work
4-5 M8 washers Fastener to space the large gear clear of the motor retaining bolt heads. Some designs and kits use a printed spacer.
Idler
1 608 bearing, skateboard bearing Bearings
1 (M)8×20 Threaded rod
4 M4×60 or M4×45 hex head bolts Fastener Hex head will work best (they won't turn), and longer than 45 mm will be easier to assemble if you can find them.
4 M4 nuts Fastener typically wing nuts
8 M4 washers Fastener
4 ~4mm ID springs Spring Sized to fit over an M4 bolt, unsprung length of 10-12mm, each spring providing 25-35N load. For a given filament drive force, you'll need about twice the spring force - i.e., if you want 100N of filament drive, your springs need to push with about 50N each.
16 M4 washers Fastener optional; 4 washers on each M4X45 idler bolt between the main block and the idler block will limit the idler travel and make reloading filament easier.
NOTE: Some users have their extruders working without springs, but springs are recommended. A good source for these springs is in the cloth-cabinet on spring loaded skirt-hangers or trouser-hangers. Just cut the right length off the springs.
Hot End Mount
2 M3×35 bolts Fastener
4 M3 washers Fastener
2 M3 nuts Fastener
1 2.5mm drill See section Hot End
Stepper Motor Mount
3 M3×10 bolts Fastener Low profile bolt heads might work better here
3 M3 washers Fastener
1 M3 grub screw Fastener To secure the pulley, ideally 8mm long, but anything 6mm+ should be fine
1 M3 nut Fastener To secure the pulley
Stepper Motor
1 NEMA 17 bipolar stepper motors Stepper 0.49 Nm (69 ozf*in) works well; Kysan 42BYGH4803 is what I used. Should be capable of creating a holding torque of at least 0.4Nm (56.6 ozf*in), at the very least.
Extruder Mount
2 M4×20 bolts Fastener
2 M4 nuts Fastener
2 M4 washers Fastener

Assembly instructions

A visual guide is available.


Inserting the short rod into the bearing to make the idler is easy if using a threaded rod. If using a smooth rod, it can be a tight fit. It is necessary to ensure that the cut ends of the rod are well finished, preferably with a slight chamfer (using a hand file) to guide it into the bearing. Careful use of a vice can then press the rod into place, with washers being used to get it past the end of the bearing to the middle.

The Hobbed Bolt

On how to make a Hobbed Bolt, see Making a Hobbed Bolt. That done, mount it like this:

M8 2inside.jpg
Note 1 - I prefer to use a Nylock nut on the end of the M8 shaft. Locktite should work as well, or a longer bolt with two nuts.

M8 2gears.jpg

So far so good! If you add 3 or 4 M4 washers on each bolt before you put the idler block on, it will reduce the idler block travel when loading new filament, making loading new filament much easier.

Here's the test jig:

M8 test jig.jpg

This extruder hit 16 kg - here's the results: M8 shoulder bolt - 7.0kg, adjusted tension, new springs - 11.0 kg,

Tightened springs, 3 trials:

15.5 kg, 16.5 kg, 15.25 kg

The final failure mode was the stepper running in reverse, as opposed to the filament slipping. That's quite promising.

The Hot End Mount

Brass-barrel.png

Attach a length of 16 mm PTFE using the two M (M3x35?) bolts to pin it in place. The holes in the ABS motor mount are 2.3mm diameter and are designed for thread-forming after being drilled to 2.5mm (2.3mm is very tight for M3 - M3's have a 2.387 bolt diameter and must be pre drilled 2.5mm for thread-cutting and even drilled wider for thread-forming, but plastic is very soft Threadinfo).

According to Nophead the holes should be drilled to 2.5mm, then you should insert the PTFE Insulator and drill a 2.5mm hole through both using the ABS part as guide. After the first hole is done insert a nail or second drill into the existing first hole to lock the teflon cylinder in place and prevent it from turning. After that use a M3 to thread-form the thread (one could also try to use a M3 tap drill (thread-cutter) and finish the mount, but thread-forming will do). The Teflon is very soft so it is very easy to thread-form. In the end the extruder should fit tightly.

Wade suggests that the nozzle can be built straight and is screwed into the PTFE (Teflon) cylinder from the bottom. There is no need for a PEEK bar or extra screws to hold the nozzle to the carriage.

Nophead's opinion is that unsupported PTFE may be OK for PLA but not for the higher temperatures and pressures ABS needs. He recommends a PEEK insulator with a PTFE liner or an external support which would need an adapter plate.

Mendel_extruder

I use 8mm od brass rod, with a 4 mm ID melt chamber, insulated nichrome wire and furnace cement to hold it all together.

3D CAD Files

Here's the design files for the latest version:

Finally, here's a spreadsheet to help calculate the proper feedrates: media:feedrates.ods | media:feedrates.xls

An updated version of the spreadsheet to use with Skeinforge, somewhat simplified. I vary the layer thickness, width/thickness and the two speed settings until I get a density near unity for nicely solid solid parts: media:Extruder Calcs 2010.07.13.ods

Variations on this design

laser-cut variant of Wade's extruder, as used in Huxley Seedling.

Alternative filament drive bolt: http://suddendevelopment.com/?p=68

Older versions

Here is a link to a previous version of this page that describes an earlier version of this extruder that uses an M4 shaft, and includes more details about pull testing the two versions: Geared_Nema17_Extruder_V0.5