DWG 3D Printer 2nd battle

created by Łukasz Jakóbiec date: 16/10/2015

Łukasz Jakóbiec 16/10/2015 DWG 3D Printer 2nd battle

After the initial build of the printer several issues with SPECTRA line and printer size made it clear that it will not work with required precision with sufficient speed.

So my observations are as follows:

  • SPECTRA line should be over 60kg strong (mine was 20kg)
  • bigger the print area and more visible is SPECTRA stretching (this was most noticeable in the long Z Axis)
  • Spools for the SPECTRA for big printers are easily getting BIG. Also printing them in PLA is a no go.
  • Building Z Axis with SPECTRA longer than 200mm can get tricky quite fast

Because of this issues I went with more proven design with GT2 belts in X Axis. I left SPECTRA line in the Y Axis after upgrading to heavy duty line (over 80kg strength) and changed Z Axis to ground C5 precision ball screw that was originally bought for my CNC mill. Z Axis is driven by 100W AC servo that has 2048 encoder pulses so the Z precision is outstanding.

This is my second print after all upgrades. Layer height is 0.12mm with no visible variations on the layer height 

Going with the Z Axis of the highest quality is in my opinion the best way to make high quality prints. Second thing is to make it stiff. It cannot wobble. It cannot flex. Otherwise you will constantly readjust the bed and making the printing process a simple "print" button action with always fail.

The upgrades

  • THK42 rail with two SRS15WM carriages 
  • welded bed "triangle" to make it stiff and make levelling easy and precise
  • W1506FA-C5T NSK Ground Ball 550mm usable length

  • bed is heated by 600W 220V silicon heater driven by SSR relay
  • bed is made of precision aluminium plate level up to 0.1mm
  • print head has a induction end stop integrated
  • X Axis is driven by two GT2 belts on both sides of the axis
  • ATX PSU has been replaced by smaller 10A 12V PSU as the heat bed is powered directly from the mains power
  • Z Axis is driven by 100W 220V AC servo with closed loop position control
  • cables are organised into harnesses with appropriate connectors and shields
  • printer will have an enclosure :)

The Z Axis

To make Z Axis movements controlled and repeatable the axis is held together by welded triangle and rides on THK wide rail.

the "triangle" in all its glory
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triangle being fitted. The rail is printer backbone.

To make this crucial axis precise and repeatable and fast I went with professional servo drive. 

servo pack driving the motor

this small motor has nominal output of 100W and can be overloaded up to 300% for 10 seconds
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complete Z Axis with further assembly ongoing
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For driving servopack you can use signals driectly from the 5V logic eg. RUMBA board with AVR. The enable signal requires 24V so small additional PSU is needed. Ot the input can be shorthned to ground to make it permanently "ON". I prefer the abiity to switch powerpack OFF when not in use to make less stress on the drive.

breaking out controlling signals from step stick connectors on the RUMBA board
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STEP, DIR, ENABLE, 5V and GND (STEP and DIR is differential so positive has to be connected to 5V and negative has to be driven by AVR on RUMBA board) 
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After all the upgrades this is how it looks now.

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