Saturday, 28 October 2017

Building a Prusa i3 MK2 from Scratch

Prusa i3MK2 'Sculptor"
    So, time to reveal what the mystery replacement for the Micro Kossel is, I've repurposed the electrical harness into a Prusa i3MK2 clone build. Sourcing the parts was a bit of a nuisance, but most of it had close matches at my local hardware store or was stuff I had on hand.
Imperial equivalents of the M8 (5/16") and M10(3/8")
 with 1/4" threaded rod for the z-axis screws
Idler arm for the extruder with a 625 bearing from OpenBuilds
     Now, some of the parts for this machine do require CNC cutting normally, but following some of the tricks used by Tom's 3D build from march, I printed the frame template on paper, glued it onto and cut it out from some 3/4" plywood for the frame and 1/4" plywood for the y-carriage.
3/4" plywood frame with template attached
Frame and y-carriage ready for painting
     After cutting out the wooden parts, the next step was to paint and seal them, otherwise they'd change size with the ambient humidity. I used some black acrylic for the first coat, then followed up with a coat of Varathane to seal them.

Main frame waiting for paint to dry
Y-axis parts and tools
     While waiting for the paint to dry I moved on to assembling the y-axis/base frame. Assembly is fairly straightforward, only major thing that you need to watch is that the frame is completely square and flat. Squaring the frame is fairly simple with an old woodworking trick, just take a tape measure and check that both diagonals are the same length, if they match the frame is square in that plane. As for making sure it was flat, I used the one surface in the workshop guaranteed to be perfectly flat, the top of the table saw.

Checking the diagonals for squareness
Checking the other diagonal
     Once that was assembled, the next step was adding the vertical frame, then installing the x/z-axis assembly followed by the extruder carriage to complete the primary frame assembly.

Main frame assembled
Extruder ready for installation
    With the Extruder installed, it was time to sort out where to mount the main control boards. The normal place for them is on the back left of the main frame, but the cables on the LCD module I'm using are only 10cm long, so I've mounted the Ramps package on the front left side with the power block on the back.

Installing the Ramps casing (Thing:761806)
Power brick with custom brackets
Raspberry Pi Zero W for Octoprint host
    I designed a couple custom L-brackets for mounting the power supply and Pi camera, with those installed, it was time to sort out the firmware and calibrate the z-height. For the print-bed, I'm just using a sheet of Buildtak stuck to some 3/8" plywood, basic but workable.

Completed i3MK2
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