AgeingHippy Wrote:
-------------------------------------------------------
> Hello All
>
> I used Reprap Host to generate a gcode file.
> Looking at the file some strange activity is going
> on which I do not clearly understand.
>
> ; GCode generated by RepRap Java Host Software
> ; Created: 2011-01-03:12-29-38
> G21 ;metric is good!
> G90 ;absolute positioning
> M140 S55.0 ;set bed temperature and return
> T0; select new extruder
> M113; set extruder to use pot for PWM
> G92 E0 ;zero the extruded length
> G28; go home
> G92 E0 ;zero the extruded length
> G1 F5.0; feed for start of next move
> G1 Z0.4125 F50.0 ;z move
> G1 Z0.5875 ;z move
> G1 Z1.0 F5.0 ;z move
> G1 F1500.0; feed for start of next move
> G1 X2.8 Y0.1 F3000.0 ;horizontal move
> G1 X127.2 Y4.9 ;horizontal move
> G1 X130.0 Y5.0 F1500.0 ;horizontal move
> G28 Z0 ;set z 0
> M109 S190.0 ;set temperature and wait
> G1 F3000.0; feed for start of next move
> G1 E1000.0; extruder dwell
> G1 F1500.0; feed for start of next move
> G1 F18000.0; feed for start of next move
> G1 E960.0; extruder retraction
> G1 F1500.0; feed for start of next move
> G92 E0 ;zero the extruded length
> ;#!LAYER: 1/66
> code continues with layer 1 gcode
>
> Now I understand setting the temperature and
> zeroing the extruder position etc but I do not
> understand
>
> G1 F5.0; feed for start of next move
> G1 Z0.4125 F50.0 ;z move
> G1 Z0.5875 ;z move
> G1 Z1.0 F5.0 ;z move
Because it is using acceleration. I.e. start at 5mm/ minute and then accelerate up to 50mm/m, then constant speed and then decelerate to 5mm/m before stopping. All very slow! I accelerate to 5mm/s over 250 steps.
>
> Seems to move the extruder to 0.4125mm then to
> 0.5875mm then to 1mm.
> Why does it not simply move directly to 1mm?
>
> G1 F1500.0; feed for start of next move
> G1 X2.8 Y0.1 F3000.0 ;horizontal move
> G1 X127.2 Y4.9 ;horizontal move
> G1 X130.0 Y5.0 F1500.0 ;horizontal move
>
> Moves to X2.8 and Y0.1
> then moves to X127.2 and Y4.9
> then moves to X130 and Y5.0
>
> Why not move directly to X130 and Y5.0 without the
> intermediate moves?
Again all for the acceleration. G-code has no acceleration notation, so Adrian accelerates from the last speed to the specified speed in the firmware, or at least that is my understanding.
>
> G28 Z0 ;set z 0
> M109 S190.0 ;set temperature and wait
> G1 F3000.0; feed for start of next move
> G1 E1000.0; extruder dwell
> G1 F1500.0; feed for start of next move
> G1 F18000.0; feed for start of next move
> G1 E960.0; extruder retraction
> G1 F1500.0; feed for start of next move
> G92 E0 ;zero the extruded length
>
> We then move to Z0, set the temp and wait till it
> is reached.
>
> Then extrude 1000mm of plastic?? what is going on
> here?
>
> We set the feed rate twice. first 1500 and then
> 18000 and then retraqct the extruder by 40mm
>
> All this is preparation before the first layer is
> printed. Could anyone please clarify what is going
> on here?
>
> Thanks
I am not sure exactly but during warm up the extruder tends to empty itself as the plastic expands so you need to prime it before the build by extruding say 50-100mm of plastic and then retracting to stop it oozing as it moves to the first point to be extruded.
[
www.hydraraptor.blogspot.com]