Models not printing correctly

Can someone please help? Quite a few models i have tried to print lately start to print perfectly well, and then about 20 layers up just decide to sort of 'step' 5mm or so in one direction, carry on fine for a while perfectly and then it will step again, not necessarily in the same direction. Initially i thought this was a hardware related problem, but as the printer has practically now been completely taken apart and rebuilt from scratch, addressing some of the issues i found on the initial build (the x and y axis belt tensioning instructions are quite frankly a joke, thanks to all on the forum who have come up with sensible suggestions), i am now convinced that is a software issue, more specifically a slicing issue. I have tried various slicing software (possibly too many?), so have gone back to the standard pronterface with built-in slic3r on a clean installation of windows 7 x64. I should also state that i have printed the same models more than once, and the stepping issue happens in exactly the same place every time, so please don't suggest the problem is to do with 'belt-tensioning/slipping, i'm 99.9% sure this is not the case. I have pasted the slic3r .ini files below, in case anyone can spot something obvious that i have missed, and also attached some photos.

filament\ormerod.ini :

# generated by Slic3r 0.9.9 on Mon Jul 14 09:34:58 2014
bed_temperature = 62
bridge_fan_speed = 100
cooling = 1
disable_fan_first_layers = 1
extrusion_multiplier = 1
fan_always_on = 0
fan_below_layer_time = 60
filament_diameter = 1.75
first_layer_bed_temperature = 67
first_layer_temperature = 190
max_fan_speed = 100
min_fan_speed = 35
min_print_speed = 10
slowdown_below_layer_time = 30
temperature = 185

print\ormerod.ini :

# generated by Slic3r 0.9.9 on Mon Jul 14 09:34:33 2014
avoid_crossing_perimeters = 0
bottom_solid_layers = 3
bridge_acceleration = 0
bridge_flow_ratio = 1
bridge_speed = 60
brim_width = 0
complete_objects = 0
default_acceleration = 0
external_perimeter_speed = 70%
external_perimeters_first = 0
extra_perimeters = 1
extruder_clearance_height = 20
extruder_clearance_radius = 20
extrusion_width = 0
fill_angle = 45
fill_density = 0.25
fill_pattern = rectilinear
first_layer_extrusion_width = 200%
first_layer_height = 0.3
first_layer_speed = 30%
gap_fill_speed = 20
gcode_comments = 1
infill_acceleration = 0
infill_every_layers = 1
infill_extruder = 1
infill_extrusion_width = 0
infill_first = 0
infill_only_where_needed = 0
infill_speed = 60
layer_height = 0.3
min_skirt_length = 0
notes =
only_retract_when_crossing_perimeters = 1
output_filename_format = [input_filename_base].gcode
perimeter_acceleration = 0
perimeter_extruder = 1
perimeter_extrusion_width = 0
perimeter_speed = 30
perimeters = 3
post_process =
raft_layers = 0
randomize_start = 0
resolution = 0
skirt_distance = 12
skirt_height = 1
skirts = 2
small_perimeter_speed = 30
solid_fill_pattern = rectilinear
solid_infill_below_area = 70
solid_infill_every_layers = 0
solid_infill_extrusion_width = 0
solid_infill_speed = 60
support_material = 1
support_material_angle = 0
support_material_enforce_layers = 0
support_material_extruder = 1
support_material_extrusion_width = 0
support_material_interface_layers = 0
support_material_interface_spacing = 0
support_material_pattern = rectilinear
support_material_spacing = 2.5
support_material_speed = 60
support_material_threshold = 0
threads = 2
top_infill_extrusion_width = 0
top_solid_infill_speed = 50
top_solid_layers = 3
travel_speed = 130

printer\ormerod.ini :

# generated by Slic3r 0.9.9 on Mon Jul 14 09:35:26 2014
bed_size = 200,200
end_gcode = M104 S0 ; turn off temperature\nG28 X0 ; home X axis\nM84 ; disable motors
extruder_offset = 0x0
gcode_flavor = reprap
layer_gcode =
nozzle_diameter = 0.5
print_center = 100,100
retract_before_travel = 2
retract_layer_change = 1
retract_length = 1.4
retract_length_toolchange = 10
retract_lift = 0
retract_restart_extra = 0
retract_restart_extra_toolchange = 0
retract_speed = 30
start_gcode = G28 ; home all axes
toolchange_gcode =
use_relative_e_distances = 1
vibration_limit = 0
z_offset = 0

I've used lots of different versions of slic3r (I'm currently using 1.1.6), and I've never seen it generate unwanted steps in the output. The way to check is to run the gcode through a gcode viewer/simulator, such as the one at [gcode.ws].

Which firmware version are you running? Some firmware versions have acceleration bugs, which can cause the stepper motors to skip steps, giving rise to the issue you describe.

What stepper motor currents are you using? Increasing them may help, in particular I suggest 1000mA for the Y motor.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

What printer firmware are you running? I think one of the earlier versions had a bug where it printed things way too fast when connected over USB, and the acceleration from that could very well cause the motors to skip steps (if the belts hold up properly, the motor is what will give way). That it happens in the same spots is probably just because that's where you have the most acceleration.. The prints sure do look like either the belt or the motors slipping, and there is some other artifacts that I think are consistent with printing just happening too fast.

Edit: Curse my metal body, I wasn't fast enough

Edited 1 time(s). Last edit at 07/16/2014 05:05AM by jstck.

sorry, i should have mentioned these details in my initial post , but this printer has been annoying the hell out of me.

printer is running the latest firmware i could find on github.
slicer is v0.9.9. will try newer version
motors are the ones suppled with the kit from RS labelled JK42HS34 1334A. have no idea what mA they run at, or how to adjust them?
i have been running all my gcode files through a viewer, and they all view fine.

Quote
[email protected]
printer is running the latest firmware i could find on github.

Yes, but WHAT VERSION? Use the M115 command to find out.

If you look in your config.g file, you will find the M906 command that sets the motor currents.

Edited 1 time(s). Last edit at 07/16/2014 07:15AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

To me it looks like the motors are skipping steps.

In the config.g file in the sys-directory on the SD-card there should be a command M906 that sets the current through the motors. I have this line in mine:
M906 X1000 Y1000 Z1000 E1000 ; Motor currents (mA)

It sets the current on all motors to 1000mA. I don't know if it is really necessary, but the the motors don't get too hot, neither are they skipping steps.

How are your linear bearings running. I had one baring gone bad, which caused to motor to skip steps from time to time. It's likely the rubber-seals that get pushed into the bearing

:-) Carsten

I suspect you are using firmware with the acceleration bug, or perhaps your belt is too loose and slipping a tooth every now and then.

Dave
(#106)

firmware is 0.65e
have changed motor settings
have changed PSU
has made no difference

0.65e does appear to have an acceleration bug, but I don't know what triggers it. Try RRP 0.78 or my 0.78d-dc42 instead. Read the notes on changes to Z probe wiring and config.g that you need to make when going from 0.65x to 0.78x.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

have updated the firmware on the duet board and sd card and have (eventually) found the notes i had to read.
i am not, and have no desire, to become an electronics expert. how do i know which wire is the signal output? how do i know which is the trigger/modulator input? T goes to D52?
i know people are trying to be helpful, but please remember, if everyone had the same level of knowledge then they wouldn't be asking for help on a forum really would they?

If you are using the standard Z probe, you don't have a trigger/modulator wire, so just ignore it in the diagram.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I've updated the wiring diagram to show where the blue wire from the sensor (which is the signal wire) goes now, with the 0.78 firmware. See: [reprappro.com]
Make sure you update the files on your SD card to match the firmware. Regarding the step in the prints issue, it may be a mechanical problem; see the troubleshooting guides here: [reprappro.com]
Also, your extrusion doesn't look very consistent; the filament may not be extruding well. See: [reprappro.com]

Sorry you are having difficulty, but to progress the firmware (fixing bugs, adding new features) we sometimes have to revise things we did earlier. The forum is populated by other Ormerod owners, who are more than willing to help, even though not obliged to. You can contact me directly for support by email on support at reprappro dot com.

Ian
RepRapPro tech support

finally seems to be sorted out. thanks to everybody for their help.