Failed Print - How to restart at last good position

[diamonddog 0]

I am new to 3D printing and started to print my 1st BIG item on the LONGER LK5 PRO

The print after 80 HOURS of printing while i was away from home somehow failed so badly that the clips from the print bed were found 1/2 way across the room

and the print was printing 1/2 in air and 1/2 on the print. I did manage to salvage the print that has already been done and best guess is that its last positive position was

at or around 254mm, How do i edit the GCODE so it starts at that point FLAT on the bed with supports etc??

 

 

[conductive_printing 1]

so you're trying to print a second part that starts at 254mm?  you can set the model at Z=-254mm in cura, and it should slice just like a normal part.

[GregValiant 1,261]

I have a different take.  This part is not good.

"somehow failed so badly that the clips from the print bed were found 1/2 way across the room".

And that happened with the print head at 254?  The print head whacked the print for some reason.  You need to know what happened so you can keep it from happening again.

If the print moved on the build plate you can forget about it.  There just isn't any way to align the failed print so it is right where it was.  The second problem is that very few printers have end stop switches that are repeatable.  The ones on my Ender can be off +-0.25mm.  Then there is the possible rotation about the Z.  Nope.  If it moved on the build plate there is no way.  If the print somehow styed in place and you allowed the build plate to get cold you are in trouble as the print may be ready to pop loose.

 

If it didn't move then you have a slim chance.

The first problem is that you must auto-home in order to tell the printer where the nozzle is.  Do you have room?  You can use G28 X Y to home those axes and that can happen with the print head up high, but is there room to bring the print head and gantry down to the build plate without mashing the part when you home the Z?  The Z normally Auto-Homes in the left front corner but that doesn't need to be so.  You could home the X Y up high, move the nozzle to the right rear corner, and then use G28 Z to home over there.

 

You need transition gcode to go from nothing, to continuing a print at (we'll call it) 254mm.  The first thing is to manually move the print head above the print.  You do not want to start by smashing the print.  You would do a SaveAs of the gcode file and delete just about everything up to the layer where Z=254.  Note the last X Y position that would be the start point of the new layer.  Also note the last E number of the last layer.  If there was a retraction it will be on it's own line like G1 F2100 E2345.65432

1. M109 S for the hot end temp
2. M190 S for the bed temp
3.  G28 X Y
4. G1 X?? Y?? F3000 ;Move to a place where the Z can drop to the bed.
5. G28 Z ;home the Z in a clear place
6. G1 Z265 F2100 ;Get the Z up above the print
7. G92 E0 ;reset the extruder
8. G1 E15 F300 ;Purge the nozzle
9. G92 E???? ;Set the E location so it is correct for the start of the print.
10. M221 S110 ;Kick the flow up for the restart and hope it gets good adhesion to the top existing layer.
11. G1 X??? Y??? F6000 ;Move to the start point of the first extrusion.  The number will be from the gcode.
12. G1 Z??? F300 ;Drop the Z down to the working height.
13. G1 Fxxxx ;set the print speed in mm/min
14. Close your eyes and hit the print button with your fingers crossed.
15. At the next layer put in M221 S100 to drop the flow back down.

I've done this several times.  There is almost always a layer-shift-looking-line as the X and Y rarely home to the exact same position.