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Who Prints the Printer?

One in Three

That’s how many prints finished successfully on my MakerBot Replicator 2.  I knew what I was getting into when I started 3D printing, but for a commercial product, that’s bullshit.  Apparently this is a common problem. Check out these galleries dedicated to 3D printing failures ranging from plastic spaghetti to bizarre distorted horrors.

Some quick Googling revealed that my printer actually has a rather serious design flaw.  Imagine that the ink on your 2D printer stopped flowing to the head. That’s what’s happening here.  The good news is that you can print out a solution right on the printer itself. How very meta!

The Problem

TL/DR: Keeping the 3D printer “ink” flowing is complicated.

3D printers are basically robot arms with a hot plastic gun (the “print head” or extruder) attached. Plastic filament (wire) moves through the print head where it is melted and forced out a nozzle and onto a print bed made of glass or acrylic, where it solidifies. A computer processes a 3D model into coordinates that move the extruder around so that the line of melted plastic forms an outline of a structure.  This is done layer by layer until the item you want to print is formed.

In the MakerBot, the filament is pulled into the extruder with an electric motor with an abrasive feed wheel attached. Filament comes into the top of the print head and is pulled along by this wheel.

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A small plastic piston pushes the filament against this wheel to help guarantee that plastic feeds into the extruder.  Over time, this piston wears down and puts less pressure on the filament.

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When this happens, the filament “stalls” and plastic stops extruding, resulting in an incomplete print. If it starts again, melted plastic rains down over the model. In the worst case, your extruder gets clogged with burned plastic.

The Solution

TL/DR: Print the fix yourself or buy it on eBay (search for “Makerbot extruder upgrade”).

The 3D printing community is a creative bunch and developed a solution to the problem. A kind soul named whpthomas at Thingiverse.com engineered a replacement part that you can print out yourself!  This part replaces the stock piston with a spring-loaded arm that provides 60N of force on the filament.   

So, how do you reliably print parts to fix an unreliable printer?  The answer is “really slowly.” I had to reduce the print speed and watch the prints like a hawk. The arm and base printed with only one failure. They were simple, hollow parts that had rafts and supports built in. The pin, on the other hand, was solid and required 6 prints to get a single usable piece. 

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You’ll also need some metal hardware:

  • 3/8” x 1-1/8” x 0.041” compression spring
  • M3x8 and M3x10 counter-sunk (not counter-bored) hex head bolts (obtained at Ace Hardware; easy link for Portlandors)
  • 3mm ID x 10mm x 4mm bearing (obtained at any local Fastenal)

Of course, you could just order the right stuff here 🙂

Assembly is relatively easy. Press fit the plastic pin into the arm until it’s flush. Screw the bearing into the L-tip of the arm (this bearing actually presses filament into the abrasive wheel). Screw the base onto the motor. Press the plastic pin on the arm into the base. Install the spring between the nub on the arm and the nub on the base. Here’s what it looks like all assembled on the feed motor.

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In case you were wondering, plastic filament enters the feed assembly through the hole on the arm. 

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I think MakerBot was expecting their users to be fiddling with their printers. Disassembling the print head was surprisingly easy. You just removed two very long screws and the whole thing comes apart. The upgraded feed assembly drops into place.  Detailed instructions are included at the link below.

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 The Verdict

Misprints were all but eliminated after performing this upgrade. I could successfully print new models in one go. I could print really large items unattended, that I’d previously had to carefully monitor.  I could use almost any kind of filament I wanted without worry.  You’ll get to see some of those prints in the coming days.

This experience has highlighted the perils and the promise of 3D printing for me. It’s clear that 3D printing is in its infancy and I’m strongly reminded of the state of personal computers in the early 80s. Early PCs required a lot of knowledge and patience to operate, but eventually became so easy that anyone can pick one up and be productive in no time flat. In fact they are being supplanted by smartphones and tablets, which require barely any effort to use.

Though it’s a drag to discover serious design flaws in a product that I paid so much for, fixing the problem was relatively easy and MakerBot is being a lot more open about the problem than early PC manufacturers.  Was it frustrating? Yes. Will this fix last? I don’t know. Will something else turn up? Probably.

Whatever the case may be, I’m going to print my way to the sunset. Onwards!