Monthly Archives: January 2019

3D Printing: Ashtar C Printer: 1st Prints

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Back in September 2018 I started to code the first parts for Ashtar C, a “Core XY” type 3d printer – finally, after several weeks waiting for the several parts (bearings, closed loop belts), I was able to finalize the bed and Z axis (2018/01/30) and perform the first test prints of Ashtar C #1 composed with 500mm 2020 T-slot and V-slot alu extrusions:

Specifications

  • CoreXY style
  • Build Volume: 380 x 400 x 380mm
  • Frame Size: ~500 x 500 x 500mm

Bed

  • 400 x 400mm black bed sticker (~0.7mm thick)
  • 400 x 400 x 4mm mirror (custom order)
  • 4x bed corner mounts (printed), with M3 x 30 and spring and 4x washers each
  • 420 x 420 x 4mm OSB

residing on 2020 T-slot alu extrusions.

Z Axis

  • 1524mm GT2 closed belt: even though driving 4 threaded rods worked somehow, but not reliably therefore:
    • Option A
      • 2x Nema17 (45Nm) stepper motor with 18 teeth GT2 pulley 5mm bore
      • 2x 760mm closed beltbelt-routing-z-axis
    • Option B
      • Using 3 or higher : 1 gear box (e.g. 3:1 gearbox could be used, but external shaft isn’t strong enough stabilized versus tilt) or alike to increase torque and still drive 4 threaded rods
  • 4x M6 x 490mm threaded rods
  • 4x M6 nuts with bed mounts (printed)
  • 4x bottom Z rod mount (printed)
  • 8x 606ZZ bearings (each rod has 2 bearings)
  • 4x 18 teeth GT2 pulley 6mm bore

20190130_170822

20190130_170838

Challenges

Following challenges came up in the first test prints:

  • CoreXY principle works well, yet, the friction of each idler really matters as it increases risk of missing steps, well greased and well positioning mandatory
  • X endstop: right now positioned on the left hand side of the X beam, but the cable hangs down – likely need to reposition X endstop on the X carriage itself
  • the Bowden tube is long and so hangs to the bed, the tube (4mm OD, 2mm ID) isn’t stiff enough to bend upward, so requires some guidance to ensure it doesn’t ride on the bed surface and entangles with print process
  • E3D V6 clone this time really does not perform well: extrusion is not even, and missing steps of the extruder; requires further investigation.
    • thermistor seems off, increasing to “220C” print temperature, gave better and cleaner prints

Impressions

That’s it for the moment.

3D Printing: Ashtar C Printer: CoreXY Belt Routing

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After some delay of parts, I finally was able to finalize the belt routing and configure the firmware for Ashtar C #1:

Belt Routing

belt-routing

CoreXY belt routing of Ashtar C

Early on I decided to separate belts of motors A and B in the Z axis, so they would not cross as such, and also hoped one axis of the carriage holding the X beam would allow some idlers to redirect the belts – to save space and keep frame dimension and build (or printable space) dimension close.

The Bowden tube and the wires of the hotend are preliminary arranged:

20190101_170842

Firmware

To configure the Marlin firmware turned out not that simple, as CoreXY has its own interdependencies of A & B motors: first X axis was reversed, whereas Y axis worked correctly, the INVERT_X_DIR setting on Configuration.h of Marlin did not help, it reversed the stepper motor direction, but not the actual X axis direction. After many attempts to use COREYX instead of COREXY I ended up

  • swap cables of A & B stepper motors
  • keep #define COREXY
  • #define INVERT_X_DIR = true and #define INVERT_Y_DIR = true

and X and Y direction worked correctly.

Preflight (no extrusion, just X & Y axis movement testing):

The stepper drivers still need some tuning, as I saw or rather heard a few missed steps at fast movement.

X & Y Endstops

The preliminary positions of the endstop are:

  • X endstop resides on the X beam left-hand side (USE_XMIN_PLUG)
  • Y endstop resides on the right-hand backside, (USE_YMAX_PLUG and HOME_DIR_Y 1)

Z Axis

I postponed the actual details of the Z axis, as my main concern of the design was to have a good CoreXY setup and then see how I would achieve the Z axis.

In order to use 625ZZ bearings I started to use them as idlers directly (after cleaning the grease off their surfaces) and also use them to increase contact surface when driving a closed belt which drives 3 or 4 threaded rods M6 x 500mm:

20190101_124138

Since the surface of the threaded rods is rough, I realized I need dedicated bearings to hold the rods at the bottom, otherwise the friction would wear on the mounts and increase its diameter. So, the Z axis isn’t finalized yet, but close.