Dr. Lawlor's Code, Robots, & Things

December 9, 2012

Printrbot Assembly: 2012 Howto

Filed under: 3D Printing, Printrbot — Dr. Lawlor @ 8:34 am

Last month I built up a Printrbot Plus kit, which was a lot of fun and seems to be printing well.  But both the hardware and software for this do-it-yourself 3D printing technology is still pretty immature, so here’s my guide to the current rev of that particular hardware.

The definitive place to start is Tim Stark’s official assembly instructions, a solid photo guide.  It leaves out a few problems with the current kits, though, including:

  1. At step 55, my Y motor stepper’s shaft was too short to reach the tiny setscrew.  I drilled and tapped the plastic pulley for a new lower #6-32 set screw, which still just barely reaches the motor shaft.
    Printrbot Y setscrew
  2. At step 68, while attaching the heated bed to the carriage, you need to insert *something* at least 2-3mm high underneath, or you’ll find the carriage hits the deck before the printhead even gets close to the bed.  I put an aluminum sheet under the bed to even out the heat distribution, which is pretty nonuniform by default.  My under-bed sheet is a little over 2mm thick, cut in a “U” shape to clear the thermistor.  I used the long M3 screws instead of drilling out the PCB for #6-32, but either would work.
    Printrbot bed
  3. At step 104, the 5/16″ black hex head bolt needs the whole stack listed at step 136.  If you wait any longer, you won’t be able to use a hex key to keep the bolt from rotating as you tighten the nylon nut on top.
  4. At step 142, my X carriage belt pulley was just a little too tall to clear the zip ties holding the Z linear bearings.  I sanded and filed the pulley down, and mounted it *very* close to the stepper surface.
    Printrbot X pulley
  5. Many people, including me, got badly crooked gears for the extruder at step 160.  I couldn’t even fit the hex head of the hobbed bolt inside, and cracked the brittle castable material while trying to chisel some clearance.  It’s a chicken-and-egg problem if this is your only printer, but if you can get something working you can print new extruder gears.

Optional improvements:

  1. I dunked all the wood parts in urethane, which makes them look better, keeps screws from backing out, and reduces dimensional changes when humidity varies.
  2. I wanted to protect the extruder and bed wiring, since flexing back and forth repeatedly across sharp zipties will eventually cause wiring faults.  So I spiral-wound grip tape around all the exposed wiring, and ran a little steel wire out from the extruder to guide the extruder wiring into a gentle curve in *front* of the carriage. The sharp corner and stretched wires of step 168 make me wince.
  3. My Y axis belt stretched after installation, resulting in blobby prints.  I tensioned it using a rubber band hooked on a binder clip, pulling sideways to take up belt tension.  Keep it far enough back that it won’t get sucked into the stepper even when the bed is fully forward.

Lots of folks seem to get discouraged when things don’t work straight out of the box, but this is brand-new technology: you’ll need some tools, talent, patience, and creativity.  But the Printrbot is a solid kit, and with a few tweaks makes a reliable printer!


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