Printed Extruder

Update: I added a 4th part: The insulator retainer. This part not only replaces the last acrylic part from the MK3 extruder, it also solves a problem with a too high toolhead: It could happen, that the build platform got stuck with one of the bolts holding the dinos. With the new retainer plate not anymore…

Update 2 (04/01/2010): There's now also an alternative Printruder design available, kind of a Printruder MK2 (I call it "Printruder II"). See [http://www.thingiverse.com/thing:1980] for more information.

After having some difficulties with the Plastruder MK3 which comes with the MakerBot, I decided to try and print a better (i.e. more reliable) extruder with and for my MakerBot. You can download the completed design from Thingiverse.

The design was inspired by the "Thermoplast Extruder Version 2.0" from the RepRap project and by photos I saw of Nophead's "Fast extruder".

What I came up with is this:

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The extruder is built out of 4 printed parts:

The "Motor Bracket"

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The "Idler Bracket"

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The "Base plate":

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The "Insulator Retainer":

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Here a rendering with the not-yet-printable parts:

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… and here's the real thing:

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(The above image shows the toolhead with the "old" acrylic insulator retainer)

Is it working?

Oh yes! In fact, the "Printruder" in the photo above was printed by it's predecessor: The first prototype, used to print the above parts, works exactly the same way. The only difference was the base plate and the way of mounting it to the MakerBot Z stage.
The printing of the three parts (more than 3h continuous printing) worked very smooth and reliable!

How to build it

As you might already noticed: English is not my native language. If there are any syntactical or grammatical errors, please feel free to correct them!

Download and prepare the build files

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Start by downloading the build files from thingiverse.com: [http://www.thingiverse.com/thing:958]
The download contains the the STL files for each of the three parts as well as already skeinforged gcode files for direct printing. Although I used these gcode files to print the parts on my MakerBot, you might need other settings for your machine. If not sure (or if printing the gcode files fail), just use Skeinforge with your default settings to produce new gcode files.

When processing the STL files, Skeinforge throws some warnings. At least in my case, Skeinforge's fallback algorithms seem to work: the resulting gcode files were all printable without problems.

Print!

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One known problem is warping of ABS when printing large and/or massive objects.

All three parts unfortunately fall into this category.

But there's hope: As long as the warping isn't way too much (e.g. the object is ripped off the build platform during printing), it doesn't matter.
The reason is that it curls the bottoms of the parts, but not the tops, which remain flat.

For example:
When printing the base plate, the raft wasn't too good, so the part got some serious curves (it's supposed to be a "flat stick", see rendering above…):

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But as you also can see, the top line is pretty straight and that's the important section of this part.

Also the horizontal outline is still fine:
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One thing what you absolutely want to do in this case, is to re-drill (rebore?) the horizontal holes. Be careful not to break the part. Use a power drill and do not try to bent the plastic with a screwdriver or something.

[Update]: I printed a new base plate in the meanwhile (one with much less warping!). I documented the whole thing in a video:

When printing the motor bracket, I got a very good raft (and luck), so there wasn't any noteworthy warping:
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Unfortunately, the MakerBot had 4 "hickups" during the 1 1/2 hours of printing this, 2 of them in uncritical places (you can see one of these blobs of plastic in the lower left in the following image), but the other two were not so "nice". The first gave the printhead a big smack to the side when it tried to print over the (in the meanwhile hard) blob of plastic (you can see the distortion of this in the vertical middle of the object). The last one ripped the whole object inclusive build platform from the Y stage(!). Fortunately, I was sitting in front of the machine and was able to re-mount the thing in 1 or 2 seconds (ok, there were also some cuss words involved). So amazingly I didn't need to abort the print…

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The third and last object to print is the idler bracket:
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Again, the warping doesn't matter, it's on the "unimportant" side of the part.

Clean the parts up

First the obvious: Remove the rafts and cut off any blobs of plastic.

Then you might check all the holes. Often they aren't as empty as planned and due to the shrinking of ABS some holes might be too tight for the bolts.
I always use a power drill to re-drill all holes.
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(the small part in the middle is just a test print of the tenon part to check the sizing…)

The four corner holes in the motor bracket and the idler bracket are for the M4 bolts.

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Especially the four holes in the idler bracket should be a little larger. I used a round file to open them up a little bit. You should be able to move the idler bracket on the four M4 bolts later.

Assemble the Idler Bracket

You'll need a M6 bolt (30mm long), a M6 nut, some washers and a 626 ball bearing.
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Use one washer on each side if the bearing:
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Since my bolt was a little bit too long, I used two additional washers on the "front side" to avoid the bolt to stick out at the back side (which is important!)
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Assemble the Motor Bracket

You'll need three M3 bolts (30mm long), maybe a hand full washers, the DC motor from your plastruder (or a new one from [here], including the pulley) and the other 626 ball bearing.
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As you can see on the above image, the pulley on the motor has already lost the front cover. This was the result of a loose idler wheel in the MK3 plastruder. If the pulley on your motor is still complete, you might want to buy an additional pulley for this, since the printed extruder will only work with the "damaged" pulley (afaik so does the MK3 Plastruder, but please don't break your pulley and blame me for it later!!)

Anyway, try to put the 626 bearing onto the tip of the spindle. Since the 626 has a 6mm hole and the spindle has 6mm+something very small, this isn't easy (at least in my case). But that's ok. Just pay attention not to break the gears or something else in the motor.

You want the bearing half way on the spindle (or less, as long as it don't fall off).
The ball bearing is supposed to provide additional support to the motor axis.

"Load" the holes in the motor bracket with the tree M3 bolts. Be sure that the bolts aren't too long, because they might block the gears in the motor otherwise!
Since I only had M3 x 35mm bolts in my handy drawer, I used a bunch of washers on each bolt to "shorten" them…
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Attach the motor to the motor bracket. I should fit nicely in the recess in the bracket. When tightening the screws, please don't forget that the motor bracket is out of printed ABS, not out of kryptonite!
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Slide the motor bracket on the base plate

I designed the motor bracket to be tenoned to the base plate.
If there's not too much warping or other print errors, the two pieces should fit together without any additional work. It should be a tight fit, but the bracket should be able to move around (but not too slacky). If it don't fit, please try to file a bit of the tenon before breaking anything.

There's no additional need to fix the motor bracket to the base plate, since the position will be fixed by the filament (running through both, the motor bracket and the base plate).
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Mount the idler bracket

You'll need four M4 bolts (at least 60mm long), some washers, M4 nuts and (optionally) M4 wing nuts.
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Put the bolts in the four holes in the motor bracket.
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Put the idler bracket on the bolts.
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Finally add washers and nuts. Unfortunately there's only room for wing nuts on the upper bolds yet. So you need normal nuts for the lower bolts for now.
Since I'm not too happy with the 4 (wing-) nuts solution anyway, I try to find some kind of better solution for the whole thing in the future…

Mount the heater section from your MK3 Plastruder

Put the insulator retainer plate on top of the thermal barrier. The side with the bigger hole facing the thermal barrier:
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Use two M3 bolts (which used to go from the acrylic retainer plate down to the oversized washer) to attach the big washer of the heater unit to the retainer plate. Use the inner holes on the washer and put a M3 nut on each bolt before screwing the bolt in the holes of the retainer plate.
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Then attach the heater section with the M3 bolts to the base plate:
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Both, the bolts and the M3 nuts should end "inside" the base plate:
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(This photo still has the acrylic retainer plate on it, see the following for a shot with the brand new printed retainer plate:)

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Put it all together

Use the same M3 bolts as for the MK3 Plastruder to mount the Printruder to the small and big dinos.
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The big dino goes to the left (actually you'd need two small dinos, but a big and a small is all you've got, unless you have access to a laser cutter…).

Put the whole shebang in your mighty MakerBot. It should fit like a glove:
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You can still attach the electronics to the extruder (you might even use a third bolt on the big dino for that, if you want to be on the safe side.
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I'd love to have another place to mount the PCB, at least during development and testing of the Printruder. Maybe someone will design something nice to mount the PCB elsewhere…

Load the filament and try a test extrusion

I had one issue with the current design when loading the filament into the already tightened extruder mechanism: It "didn't find" the hole in the bottom of the motor bracket,
You have to be quick to switch off power, before the motor breaks your extruder!

I already changed the newest design (v3, which you downloaded from Thingiverse) to have a larger "funnel part" on the lower filament guide in the motor bracket. But I'm not sure if that's enough. So be warned!

If the driver PCB is not mounted in front of the extruder, you can see the filament coming out of the "mill" below the pinch wheel and even have a chance to help it find it's way into the hole with a small screw driver or something.

The most secure way to load filament right now is to open the idler bracket screws and to run the filament into the loose extruder. After that, tighten the idler wheel again.
The down side of this procedure besides the additional work is, that you cannot adjust the idler wheel to a well defined gap (e.g. 2mm)…

Finally, you should be able to extrude:
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Congratulations! You printed your own new extruder!

What's next?

Although the current design seems to work very well and reliable so far, there's still a lot room for improvement.

  • Better filament guidance when loading (in case the larger funnel doesn't do the job)
  • More user friendly adjustment of the idler wheel

Work in progress

I started to design a PCB holder for the printed extruder.
The first test came out of the printer badly warped!
But I tried to attach it anyway:

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The PCB holder also provides some additional support for the extruder itself.

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The triangle section is supposed to provide some support to the PCB, But it turns out that it's absolutely not necessary. I'll remove this in the next version.

I also reversed the upper bolts. There wasn't much room for the wing nuts anyway. I now use normal nuts on the other side.

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It's not much room between the body and the PCB but it's enough. I'll try to move the PCB forward in the next version anyway.

The nice thing is, that the PCB is now more out of the way for maintenance jobs on the extruder.

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You even can see the filament move inside the extruder during printing…

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