Problem with Z height when printing. (5 replies)

Hi folks. I have a problem with my i3 which I've been wrestling with since my first calibration print a couple of days ago. All my prints are coming out about 75% of the intended height. You can see it here: (supposed to be a cube!)

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and here: (1cm cubes!)

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I've double checked the Z steps/mm calibration in the firmware, and I'm really pleased with how tight it is. If I command it to rise 100mm, I can measure 99.98mm travel or better, so I don't think it's as simple a calibration issue.

My build chain is i3->Marlin->Slic3r->Repeteir (or Pronterface)

My current theory is there is a small amount of slippage in the PTE tubing that binds the Z steppers to the load screws. This would be imperceptible during a 100mm travel, but would be a compound error of significant proportions on a 50+ layer print. This was idea was given weight when I remembered that I was so pleased with the Z accuracy during calibration, that I didn't bother putting the zip ties round the tubing.

This evening I applied the zip ties, and used extreme levels of violence to get them as tight as possible. I printed another 1cm cube, but was disappointed to see only a very slight improvement in the height in Z (prob up from 7.5mm to 8mm)

I've tried this with both Repeteir and Pronterface, but there is no difference. Does anyone know if there is anything in Marlin or Slic3r that could be the cause of this?

This is the start of the gCode:

; generated by Slic3r 0.9.10b on 2013-07-05 at 23:16:44

; layer_height = 0.4
; perimeters = 3
; top_solid_layers = 3
; bottom_solid_layers = 3
; fill_density = 0.4
; perimeter_speed = 30
; infill_speed = 60
; travel_speed = 130
; nozzle_diameter = 0.5
; filament_diameter = 3
; extrusion_multiplier = 1
; perimeters extrusion width = 0.53mm
; infill extrusion width = 0.53mm
; solid infill extrusion width = 0.53mm
; top infill extrusion width = 0.53mm
; first layer extrusion width = 0.80mm

And Marlin config extract:

// default settings

#define DEFAULT_AXIS_STEPS_PER_UNIT   {80.2691,80.8389,3973.6676,695.6}  // default steps per unit for ultimaker
#define DEFAULT_MAX_FEEDRATE          {500, 500, 5, 25}    // (mm/sec)
#define DEFAULT_MAX_ACCELERATION      {9000,9000,100,10000}    // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for skeinforge 40+, for older versions raise them a lot.

#define DEFAULT_ACCELERATION          3000    // X, Y, Z and E max acceleration in mm/s^2 for printing moves
#define DEFAULT_RETRACT_ACCELERATION  3000   // X, Y, Z and E max acceleration in mm/s^2 for r retracts

// The speed change that does not require acceleration (i.e. the software might assume it can be done instanteneously)
#define DEFAULT_XYJERK                20.0    // (mm/sec)
#define DEFAULT_ZJERK                 0.4     // (mm/sec)
#define DEFAULT_EJERK                 5.0    // (mm/sec)

If I can assist diagnosis with any more data or photos let me know, any help would be gratefully received!

Jim