New to 3D

Hi All,
I've just completed building a Prusa i3 generic kit (Chinese) all good for the build process,
I've resolved the initial issue of the extrusion not adhering to the bed, but there is an issue with my print head lifting when starting to print, I've checked the bed level ( printer paper) and its good on all 4 corners, the lift is about 2-2.5mm, any hints to why this is ?

Cheers

A helium balloon attached to it, negative gravity, magic?
Sorry but without details this is a guessing and would not help in any way.
Check the settings in your slicer first...

Is it lifting because the Z-screw is turning, or due to play in the mechanism?

the Z screw only moves a minute amount when moving to the next layer, when I set all to home the extruder nozzle is correct at the zero position (and all the other 3 corners) but as it moves into print position it is obviously too high, as I'm new to whole concept of 3D printing, I'm looking for guidance as where I shouuld start looking for the answer< Downunder35M suggested looking at the slicer settings,in my case prontorface, but what should I look for ?

Maybe Z offset is enabled in the slicer

Thanks for that, I've looked in the settings and all the offsets are set to 0, maybe its in the firmware, I'll switch it on and check

Just to confirm I try to explain the print start from my point of view:
1. head homes.
2. head moves to any set offset.
3. head moves a bit more to the set layer height.

That means if you calibrate for, let's say 0.1mm from home that you actually calibrate for 0.1mm plus whatever your layer height of the print is.
If however the head moves higher during the print start you have a serious problem, so maybe try to explain it in more detail or upload a short video showing the issue!?

Does your hot end ooze filament before it stops to z-home? But 2mm is quite a lot for that problem...

---

Prusa i3, Ramps 1.4. Catnozzle 0.4mm
SketchUp - Enveloping Globoid Worm Gear - Part One - 3D Printed: [youtu.be]
DesignSpark Mechanical & more precise screw thread: [youtu.be]
Nicer Screw Thread In SketchUp ( Bolts,Nuts): [youtu.be]
How To Model A Heart Shape In SketchUp: [youtu.be]
How To Draw 3D Printable Snap Fit Ball Joint In SketchUp: [youtu.be]

Firstly, welcome to the forum.

At lot of information can be got from looking at the g-code generated by the slicer. There are some differences between the various slicing and host softwares, but for Slic3r there is an option to produce verbose g-code output, which makes it more readable. Here is the start from a simple test cube file:

; generated by Slic3r 1.3.0-dev on 2016-02-02 at 07:12:54

; Don't forget there may be a problem with gap fill
; 
; [github.com]

; external perimeters extrusion width = 0.50mm
; perimeters extrusion width = 0.50mm
; infill extrusion width = 0.50mm
; solid infill extrusion width = 0.50mm
; top infill extrusion width = 0.50mm

M80 ; turn on power
G28 ; home all axes
G0 X0 F3000 ; Get X axis out of the negative region, otherwise first moves are slow and noisy.

M109 S260 ; set temperature and wait for it to be reached
G21 ; set units to millimeters
G90 ; use absolute coordinates
M82 ; use absolute distances for extrusion
G92 E0 ; reset extrusion distance
G1 Z0.280 F15000.000 ; move to next layer (0)
G1 E-4.00000 F9600.00000 ; retract
G92 E0 ; reset extrusion distance
G1 Z0.680 F15000.000 ; lift Z
G1 X84.663 Y85.659 F15000.000 ; move to first skirt point
G1 Z0.280 F15000.000 ; restore layer Z

G1 E4.00000 F9600.00000 ; unretract
G1 F900
G1 X86.424 Y84.122 E4.12144 ; skirt
G1 X88.599 Y83.264 E4.24287 ; skirt
G1 X90.000 Y83.120 E4.31606 ; skirt

The first part is all the setup for homing the axes and warming up the bed and nozzle. Towards the end of the fragment is where the printing actually starts - lines with increasing values for E which indicate that plastic is being extruded. The most interesting thing for diagnosing your problem is the last Z value before the printing starts. You can see from my example that there can be a fair amount of messing around just before the print starts, but hopefully the last Z movement puts the head at the height you have specified for the first layer thickness. In the example above it is the line

G1 Z0.280 F15000.000 ; restore layer Z

And the Z0.280 is the height I wanted for the first layer. If you find that this value is around 2.2mm then the problem is in the slicing of the model, probably a mis-typed first layer height setting. If the value is more normal and corresponds to the expected first layer height, then we're either looking for an unwanted Z offset setting or a mechanical or firmware setup issue.

Edited 1 time(s). Last edit at 02/02/2016 07:22AM by JamesK.

Thanks JamesK,
this looks to be very helpful, I will look at this in more detail when I get home this evening, I'll report back on what I find

looked into the machine firmware, nothing pre-set apart from PLA/ABS pre-heating, then looked at producing a "verbose" G-code from Slic3r with no success,
due to time constraints I switched off the machine after checking all the levels and how parallel the X/Y guides/slides were, all appeared correct, checked flatness of the Aluminium bed, this was acceptable, I've ordered a glass plate to fit with the addition of Kapton tape and an under bed insulator sheet (cork)

My plan of attack at the weekend is to fit the new parts download a fresh .stl of the 20mm cube and slice with Cura, Slic3r and Skeinforge and compare the results after printing, this should give a better understanding of any issues generated by either the printer or the softwares

does anyone see any pitfalls with this approach ?

Sounds good. You can still read the g-code even without the verbose setting, that just adds the extra comments for readability, which makes it a bit easier to see where the major sections are.

[edit 'without' for 'with' above, changing the sense]

Edited 1 time(s). Last edit at 02/04/2016 04:56PM by JamesK.

Update,
put the stl through the works version of Slic3r (0.9.10b) and through my version (1.2.9) apart from the temperature (both versions insist on PLA) and the file size (300KB for the older version and 828KB for the newer) the runs were both succesful, no lift away from the bed and I was surprised how well the ABS filament melted @ 205c and dimensionally quite accurate, so fingers crossed that whatever caused the previous issues has cleared, I'll try another model tomorrow evening,

Regards
Paul

Glad to hear things are going well. ABS extrudes surprisingly well at low temperatures, but the layer bonding tends to be weak. You may find you need to increase that if the prints start falling apart. I run abs at the hotter end of the scale at 260C, mostly to compensate for the lack of an enclosure around the printer.