2014-10-21

Makerbot Replicator 5 gen lab notes.

For the past couple of weeks we have been playing with our Makerbot Replicator 5 generation PLA 3D printer in the office.  We use it for a project in the Exploratory Engineering department at Telenor Digital.   Exploratory Engineering is a program for allowing employees in Telenor Digital spend 3 months on a project of their own choosing.  The idea is that they get to do something that would otherwise be hard to realize, and at the end of the three months they pitch the product/project to management for funding.  Exciting stuff.

Mostly we use it to prototype enclosures for devices we are working on, but we also use it for printing various odds and ends that we need.

PLA plastic.

Previous to getting this printer I had mostly printed things using the older Makerbot products that use ABS plastics.   I had heard a lot of bad things about PLA plastics, but I have to say that it isn't that bad.  The parts are a bit more brittle and not as heat resistant.  On the other hand, the parts are much harder and more rigid.   It also seems that there is a lot less warping on big prints.  With ABS and early Makerbots I had to design and orient parts specifically to avoid warping, and it was always a nightmare with people walking in and out of the (heated) room and not closing the door after themselves.  Depending on your use this may or may not be to your liking.  For prototyping I don't find this to be a problem.

Extruder problems.

The extruder is the weak link in this printer.  Since you are using PLA, the extruder will clog sooner or later.  And chances are it will clog so badly you can't get it to work again no matter how many times you cycle it through unload/load filament cycles.

If you pick it apart I guess you will void the warranty -- but I would actually recommend you do pick it apart.  It is actually worth having to buy a new extruder rather than having to wait for 2-3 weeks for a new extruder to turn up.  If voiding the warranty is not your thing then I would advise against buying the Makerbot Replicator.

Thankfully, taking the extruder apart is relatively easy.  You have to be careful when opening the casing so you don't break the clips, but the insides are very easy to understand and to take apart. Beware that there is a spring inside which pushes against the nozzle at one end and the contact sensor on the other end.  The contact sensor is the little plastic thing with a magnet inside it.  It seems like the contact sensor actually uses a magnet and a hall-effect sensor -- which is a pretty clever design since mechanical switches aren't all that precise.

There is a video on youtube of how you do it.  The video is low quality, but it is helpful in showing you the order of operations when you pick apart the extruder.

Z-axis alignment before printing.

Before printing the Makerbot will go through a calibration procedure to determine the exact position of the Z-axis. If you have problems with the extruder rubbing against your build plate when it starts printing, it probably has misjudged the print plate position.  This will lead to the nozzle getting backed up and could end up clogging your nozzle.  You will hear a ticking sound come from the extruder, which means that the filament is slipping -- the stepper is pushing the filament but the filament has nowhere to go.

Sadly, the Makerbot doesn't have any configuration where you can adjust the Z-axis calibration and offset the print head, so instead you have to trick the calibration procedure.  What I've done is that I have 4 sheets of paper that I have cut into a long strip;  when the printer starts its pre-print Z-axis calibration I slip the sheets under the nozzle as it measures the build plate position.  Then, before it starts printing, I retract the paper again.  This way it will start printing at a slight offset over the Z-axis and it won't grind the nozzle into your build plate.

It seems that if you print things on a raft, the extruder will start a bit higher and pump out a thicker extrusion on the first pass and that this lessens the chance of getting a Z-axis problem -- but this is just guesswork on my part.

Wishlist for Makerbot gen 6

  • Make the extruder user-servicable.  It will clog and it will be more expensive to engineer an extruder that guarantees you won't have clogging than to make it user serviceable.  I wouldn't even bother trying.  Get rid of the fragile clips, at least for the main housing, and use proper torx head bolts.  Provide instruction videos for how to pick it apart.
  • The calibration/measurement sequences are slow.  Dead slow.  This smells of bad programming rather than a conservative approach.  Levelling the build plate shouldn't need to take more than 30 seconds.  The pre-print Z-calibration should be a 5-8 second affair.  I have no idea why it steps down so slowly when lowering the extruder to the plate to trigger the touch-sensing.
  • Make the firmware more configurable -- both up front and during printing.  Things like travel speed, temperature, Z-axis offset etc might as well be configurable.  If people screw up then they screw up.  (Being able to adjust travel speed while the printer is working enables you to find good settings faster since you don't have to start an entirely new print).
  • Document the network API of the Makerbot so users can easily write software for interfacing with it.  Give it a proper REST API and put libraries for different languages on GitHub. Encourage third party developers to make libraries.
  • Redesign the build plate guide and attachment.  It has a tendency to not slip correctly into place.
  • Fix the top of the extruder where the filament guide tube attaches to the print head.  It has a tendency to slip out and taping it in place doesn't work well either.  I've been thinking about designing and printing a kludge for this.
  • Make all the values editable in the print profiles.  Sure, most people who care are fully capable of editing the JSON file with the config values, but having a proper UI for doing this would be nice.
  • Make it more hackable again.  The product isn't a traditional consumer item anyway, so you might as well go back to your roots and design the thing to be user-modifiable.  If it voids warranties:  fine, I can live with that.  I'd rather risk breaking the bot and have an easier time repairing it than being guaranteed humdrum performance.

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