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
Contributors
Based-on
Categories
CAD Models
External Link


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

This extruder was designed for the RepRap Mendel (but will work on a Darwin or Huxley with adaptors) and is robust, provides a strong force to extrude, is cheap and DIY. It is an alternative to the standard extruder for RepRap Mendel 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 M3 tap;
  • no need to make splines on motor shaft;

See this extruder in action (video recorded by Casainho on 2010.08.18): <videoflash type="blip">AYH2oxYC</videoflash> View the high quality original vorbis video file.

View photos of other people's copies of this extruder.

Buy it: 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
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 5 kg*cm works well; Kysan 42BYGH4803 is what I used. Should be capable of creating a holding torque of at least 40Ncm, 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.

How to make the hobbed bolt

I used a hand drill and a file to cut the slot, then hobbed it with an M3 tap mounted in the drill, using bearings mounted in a vise to let the bolt spin - see the next videos. If you're not sure where to cut the pinchwheel slot, test assemble the extruder, making sure you leave room for the motor mount bolt heads under the 39 tooth gear, and mark the M8 bolt where it crosses the filament feed channel.

(There is an alternate method which replaces the hobbed bolt with a Dremelled bolt, see below for details).

Filing the shaft. Note: The video shows the file being held stationary as the work turns under it. When filing on a lathe-like setup you should move the file back and forth to avoid clogging the teeth of the file, uneven tool wear, and heat buildup. <videoflash type="youtube">2FU0v-3gloo</videoflash>

Using M3 tap: <videoflash type="youtube">Hl4Gf5R4YJg</videoflash>

This is a setup working without printed parts. The bearings are the ones used in the extruder later. The washer has flats to fit loosely into the vice and also holds back the tapping tool from running away. Adjust the nuts to the right to get the groove into the right place. A M5 tap was used here, which is said to be more resistant against clogging.

M8 3.jpeg

This is an earlier version with using threaded rod - it's harder to get the hobbing concentric when you cut it into the threads.

M8 1.jpg

You can also use this http://www.thingiverse.com/thing:3780 bolt hobbing tool, or this http://www.thingiverse.com/thing:1802 one.


M8 2.jpg

Using the smooth part of a shoulder bolt works better.


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.

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.

Alternate Bolt Design

Someone (if you know who, please complete with the name) at suddendevelopment.com came up with a different way to make the drive bolt using a Dremel to cut slots: http://suddendevelopment.com/?p=68.

Cloudmaker, after trying this out, noted: "I just tried this, took 5 minutes and grips incredibly, works best on the threaded part of the bolt, produces nice spikes which enter the filament :-)" and added, some longer tests later: "It works great in the original Wade's extruder, but I didn't manage to get it to work reliably in Greg Frost's variation of the Wade. A (yet to be designed and printed) rig to rotate the bolt in evenly spaced steps (12 maybe?) and to assure linear movement of the Dremel, thus giving very even spikes and even thrust to the filament, would be best for consistent even nozzle output."

An easy way to produce the teethed bolt can be found here on Thingiverse.

Closeupteeth.JPG

Myndale reports that when using this design it is imperative that all M8 nuts on the main drive bolt are kept very tight. The teeth on the bolt are cut from the original thread, and since this design results in very high grip it creates lateral forces that cause the bolt to try to unscrew itself out of the extruder. If the nuts aren't kept tight then they will rotate freely and eventually cause the extruder to jam. Note that this problem can be entirely circumvented with the use of Herringbone gears; such gears automatically self-centre and thus prevent the drive shaft from sliding out of position.

Myndale also reports that the hot end must be mounted very securely. When tested on a modified Wade's extruder with an Adrian's hot-end the resulting force was strong enough to pull recessed M3 nuts through over 1cm of infill. If your extruder cannot handle these forces then the the idler can simply be loosened, which will result in less grip and will cause the plastic filament to slip before any damage is done.

Another close-up photo showing the variation inside a slightly-modified Wade's extruder, the rows of teeth embed themselves almost entirely in the filament resulting in extremely tight grip:

Drembolt.jpg


Alternate hobbing method tuning

There is some uncertainty about the optimal nimber of cuts on the bolt's circumference. Lanthan has got an early failure (less than 10 hours printing) with 16 cuts. Better results might be expected with 12 - 15 cuts (to be experimentally determined - also, the quality of the bolt does probably matter)

Early failure s.jpg


Basic manual indexer

For a 3 - axis CNC. Better precision, calibrated cuts.

Basic indexer for hobbing.jpg

See Thing_10110

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

Stepper Driver

You should be able to use Stepper_Motor_Driver_2.3 to drive this extruder.

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