Prusa I3 Bad printing

Hi guys, don't know if this is right place to post this, but here it goes:
I'm using Prusa I3, and I'm kid of new to 3D printing. I use to get ok-good prints on the start, but not any more. I use Cura, and this settings (pic bellow). So I realy don't have any idea what to do more. I try to calibrate it as much accurate as possible and tried different settings. Any advice or solution for this problem? (model pics bellow)
Layer hights 0.1-0.2
Printing temp 185-195
shell 0.8-1.2
Thanks!
p.s. I'm using chinese filament which I get with printer.I know that is a problem but not as big as my prints are bad. And I did get some good prints on the start.
Attachment 8895 Attachment 8896Attachment 8897Attachment 8898Attachment 8899

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It is hard to see, but it looks like small steam bubbles. This can happen when your filament absorbs too much moisture. Try some dry filament to see if it improves. You can take off a length of filament to have a go at drying yourself, or buy a new roll and try that.

PS: with a cheap usb microscope you can have a better look

Thanks Alibert, I'm buying a new filament in monday and try that

Yes I would say moisture issue too. If you want to avoid it:

1. Buy high quality filament that is less prone to absorbing moisture
2. Store your filament in an air tight container when not in use
3. Before printing dry your filament out in the oven at a heat of around 50-70deg.

These are just some methods of avoiding steam bubbles

Thanks 3dex for advices, and how about this model, do you think moisture was also a problem?
Attachment 8924

Could be both over-extrusion or steam bubbles. If a lot of small steam bubbles are generated, the volume of the extruded plastic increases too. With an USB microscope you can better see what the problem is.

Hi, i bought a new filament, black 1.75mm Devil design. That fixed bubbles, but now I have problem with over extrusion. How can I fix that?

Attachment 8944 This is model printing right now

Either over-extrusion or your z-steps (how many steps are needed to move the nozzle 1 mm vertically) is wrong in your firmware.

The first you can solve in the slicer (Cura). The latter needs to be corrected in the firmware settings.

A quick check for the latter is to move the nozzle to the front of the build plate and height z=0 (nearly touching the build plate). Then manually move the the nozzle 100mm vertically (z->100). Measure with calipers if the distance is indeed 100mm. The manual moves can be either from your PC (gcodes), or from the display controller (there should be a move or jog menu). If the distance is different (80mm for example), then you need to calculate and adjust the firmware z-steps setting.

Which values I need to change to make step a little higher, this 600 to 900? or 3.3 to higher like 4?
#define DEFAULT_AXIS_STEPS_PER_UNIT {80, 80, 4000,600} // default steps per unit for Ultimaker
#define DEFAULT_MAX_FEEDRATE {250, 250, 3.3, 25} // (mm/sec)
#define DEFAULT_MAX_ACCELERATION {3000,3000,100,10000} // 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.
Thanks Alibert for reply!

Measure before dabbling!

Either you have the source code for your current firmware, or you look it up via the settings you will find in the display controller. There will be an item which defines the steps/mm for the z-axis.

Now do the measurement with the calieprs as I posted before. When you go from z=0 to z=100 mm, the firware will move the stepper moter 100 times this steps/mm value. For example if the firmware thinks it is 100 steps/mm, it will move the stepper 100*100 =10000 steps to achieve the move.

So you now know how many steps were made by the firmware, and you have measured the actual movement in mm with the calipers. Now divide the (100mm*current_steps_mm, 100*100=10000 in this example) steps by this measured value and you have the actual steps/mm you need for the z-axis.

If you design and print a 150*150*1 mm square and print this you can do the same for the x- and y-axis axis by measuring

Be aware that in the source codes, there are multiple definitions for many printers. You will need to follow the logic for the defines starting from a file called configuration.h or similar.

Hi guys, sorry for slow reply. yesterday I was calculating my steps for axis and got for E steps 112. It gives right amount of filament but it si realy slow, to slow. I don't know hot to fix that.

#define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,4000,226} // default steps per unit for ultimaker //78.7402, 78.7402,1070,865.88
#define DEFAULT_MAX_FEEDRATE {500, 500, 1.2 ,50} // (mm/sec)
#define DEFAULT_MAX_ACCELERATION {9000,9000,100,10000}

Any thoughts?

What do you mean with slow? The z-axis movement or the extrusion rate?

As to the first, that value of 1.2 may be adjusted a little upwards (it is the max speed of the z-axis in mm/s). Don't overdo it as the z-axis is the most problematic one in the i3 design and you will get artefacts or skipped steps if that setting is too high. The micro needs to generate 4000 pulses for the z-axis stepper to move the hotend 1 mm in z direction according to your defines. This means the stepper motor will need to do 5 whole revolutions (assuming a 200 step/revolution stepper). For the x- and y-directions, only 80 steps are needed per mm of movement.

According to those settings again, 226 steps are needed to push 1 mm of the filament through the nozzle, so if your true e-steps is 112, then change that 226 to 112.

PS: you might have already understood that those arrays in the defines specify the values for x, y, z and extruder motors in that order.

I mean, extrusion rate is slow (E axis is slow).
My mistake, I did put 112 for E steps.
Z steps are not the problem right now (probably the next one), don't how can I speed up those E steps, or I'm on the wrong way understanding of my problem.
And one more thing, printer is jamming realy often since I changed to new filament. (Temperatures are good 185-195C, PLA-1.75, nozzle 0.4)
I'm using this firmware for my prusa mendel i3 -> https://github.com/KapustaB/3D-Prusa-Mendel-I3-Firmware
p.s.
Thanks for a good explanation on steps.

Extrusion rate is determined by two things. The firmware settings will set the absolute maximum speed in mm/s that the gear will push the plastic filament through the nozzle. The slicer however determines at what speed it will request from the firmware when printing. You can't go too fast as the plastic will not have time to melt in the nozzle and the backpressure will exceed what the extruder gear can deliver in force.

Thanks for clarify that to me. I will try something new today. I will reset all of settings in slicer/Cura.

Quote:

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You can't go too fast as the plastic will not have time to melt in the nozzle and the backpressure will exceed what the extruder gear can deliver in force.

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Yes, I know that, but it was realy slow. I did get ok prints before.
Chears