Setting up a used printrbot

, 5 min, 913 words

Tags: hardware tinkering

Several months ago a friend with more 3D printers than time loaned me a Printrbot that needed some love. This weekend, I finally sat down and started working on it banging my head against it repeatedly.

First up was identifying which printrbot I have. Their website isn't much use, since they went out of business for a few years. After poking around a bit, my conclusion is that I have either a printrbot play or a printrbot play v2, most likely the play.

Next it was time to run the printer through its paces. I established early on that the usb connector wasn't working, which seems to be a common problem with this model. It's a bit of a pain, but luckily I can still use micro SD to communicate with the printer. (It'll unfortunately make loading new filament and calibrating the build plate a real struggle, but it's what I've got.)

So, I:

  1. Booted up Cura, loaded a model, made sure it was on the base, and saved the gcode.
  2. For microsd card printing, you need to save the gcode file as auto0.g on the card. So I did that, then plugged the micro SD in.
  3. Plug the printer in! It takes a while to heat up the build plate and extruder, but once those are at temp, it starts (trying) to print.

What I observed at this point is that no matter what I did, the extruder would start "trying to print" a couple millimeters above the build surface. Sometimes it was actually much further above the build surface, depending on where I'd positioned the extruder to start. specifically, if I start the extruder unit high up, it extrudes from high up. If I start it right on the build plate (with just a sheet of paper slipping beneath it), it is much closer, but still prints a couple millimeters above the actual build plate.

My conclusion is that the "Start G-code" (in Manage Printers -> Machine Settings) isn't zeroing the Z axis right. Unfortunately I'm not sure exactly how it should work, so that's the next step. Furthermore, because this is a fairly basic printer that doesn't reset the extruder position at the end of a job or when I stop a job manually, I can't guarantee that the extruder will always start at a fixed Z value, so calibrating this is gonna be a party!

Learning about z-axis adjustments

Next thing to do here is figure out what the heck is going on when we adjust the height of the extruder module. Some parts to be aware of:

  • The extruder: (VERY HOT) the bit that actually melts and extrudes the filament.

  • The probe: it's a bulky threaded piece with a plastic-covered bit at the end. Evidently this is what the printer uses to detect if it's close to the build plate – the probe should activate when close to metal in general. In theory you should be able to see the probe's LED (up on the top) light up if you put a metal tool near it when there's power to the printer. This isn't true for my printer right now, but might be in the future?? Which may mean I need to replace the probe. Luckily I have at least one probe sitting in a ziploc bag that I can try.

    • Another note on the probe: the printrbot comes with a little plastic spacer (a mm or so thick), and the spacer should fit snugly beneath the probe. On my current setup, there's a bit of free space, which may indicate the probe is too high up.

  • The g-code: the control sequences used to move the extruder, actually extrude/retract filament, etc.

NOTE that if the printer tries to print:

  • Too high: you get wavy looking abstract art rather than the piece you actually tried to print
  • Too low: you gouge the build plate and damage the extruder.

Talk about being stuck between a rock and a hard place!

Solutions??

Some options that come to mind:

  1. Always start the printer "zero'd" (meaning a sheet of paper can slide between extruder and build plate, but no more), manually set the "start g-code" to go down/up by the right amounts.
  2. Get the probe working and learn enough g-code that I can actually use the probe to find where Z0 should be each run. This is obviously ideal for the longer term.

Testing to work up to solution 1

Before playing with solution (1) above, I want to make sure I'm not going to damage the build plate/extruder. So I want to check that it's somewhat regular in the way it warms itself up and orients itself. To do that, I'm going to start it three times on the left side of the build plate, a paper-thickness above the build plate, and visually assess whether it starts extruding from the same height each time. It seems like it does!

Next steps

Next time I have a few hours to play with this, I'll be evaluating whether configuring the printer's settings is easier than just fixing the probe, and learning a lot more about gcode and printer internals.

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