Retraction (solved with a G92 E0 )

I have a Prusa assembled and working and am in the process of calibrating.
I've printed a few items and it works ok. I did the 0.5mm Thin Wall posted by Coasterman (thing 5573) and it printed ok, if you ignore my settings being off. I did some changes to calubrate, loaded the stl so it would generate a new gcode file. Now sometimes when it starts printing it does a really fast and long retract before starting to extrude and move. So, of course, the filament gets jammed in the extruder because it pulled it back enough so the soft plastic got up by the hobbed bolt and won't go back down in the hot end. So I have to take the bearing off the front to remove the filament.
Any suggestions of where to look to see what setting I might have messed up?
Let me know what other info would help.
thanks

Edited 1 time(s). Last edit at 12/26/2011 09:49PM by grog.

what version of SF. I use SF41 still and it's in the SF-alterations-home file for me but the later versions have changed it, might pay to go to the SF page of this forum

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Experimenting in 3D in New Zealand

Check your start alteration file. Edit it with notepad and see if the retract is there.

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Hey Grog,

I think I know what your problem is. It's been a while since I used Skeinforge for GCODE, but I my memory serves me correctly there's an option to reset the extruder before a print, I think its under Preface, and this is what the long retract is. I think by default it's selected in SFACT if you turn it off, i think that should fix it. Give that a shot.

bdc

Stay Calm out there

In the alterations folder under skeinforge, edit the start.gcode file to include a G92 E0 command to set the extruder to 0 before the print starts. Alternatively, you can issue the command from the host before sending your print.

brnrd Wrote:
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> In the alterations folder under skeinforge, edit
> the start.gcode file to include a G92 E0 command
> to set the extruder to 0 before the print starts.
> Alternatively, you can issue the command from the
> host before sending your print.

I don't find a start.gcode file in the alterations folder. the only files in there are named example_xxxx.
If I click on the Alteration button on the Alteration tab, the folder it opens doesn't have one either.
I assume it would be good to create start.gcode and end.gcode files. Other than the extruder reset file, what would be good to include? I assume a G28 to home the axis first. And at the end to get the extruder to retract slightly and move somewhere else. Haven't worried about that one much since my prints still need so much work I don't always let them complete.

NelsonRap Wrote:
> what version of SF. I use SF41 still and it's in the SF-alterations-home file for me but the later versions have changed it, might pay to go to the SF page of this forum
I believe I'm using SF40 or 41. I've looked everywhere in it to find out. Normally you can find out from the Help dropdown, but it doesn't tell me there either.

What is more odd is that it doesn't do it all of the time.

Looking at the gcode for the item, it has M113 S1.0 at the beginning.

If I have Printerface open, click Settings > SFact Settings, modify my Skeinforge settings, save and close, then load an STL file in Pronterface and have it generate the gcode file, does it generate the same way it would if I have open the STL while the Skeinforge module is still open and have it generate the gcode that way?

Preface doesn't have a way to reset.

I'm entering G92 E0 before each print and haven't had a huge retraction at the start of the print. I'm willing to enter that manually until I get a start.gcode file setup. I would still be curious as to what other settings you put in a start file.

On to the next issue. And I found the blog post about how turning off Activate Limit so it would get from home to the start of the print in a reasonable time frame.

Thanks for the help

To explain a little, If your using FiveD code the extrusion length is incremental, so for example you will see in your g code the e value starts at zero and during the print the e value gradually rises up to the end of the print. This is the total length of material extruded during the whole print, not just how much is extruded on each move.

So you start your print, the startup code may extrude a length of material to get the head working say 30mm the e value goes to 30.

Then you begin to start to print your part, the first line says something like X0 Y20 Z0.4 F200 E10. Unfortunately it assumes you are starting at no extrusion length , but in fact your extrusion so far is 30mm, this causes the extruder to wind BACKWARDS from 30mm to the 10mm asked for. This is what you are seeing at the start of the print and whats causing problems. You also get problems if you manually extrude material using your host software before printing as this raises the e value above zero.

You are correct in adding a G92 E0 just before you start printing as this sets the extrusion length to zero and stops the reversal of the extruder. Add this in the start.gcode file as the last line. You need to activate this also in skeinforge using the tick boxes found in the alterations tab.

Skeinforge
You are best looking in your directory structure to find the \skeinforge_application\alterations directory for the file start.gcode

SFACT
Your trying to find start.gmc . There are two locations depending which python script your using, but the directory structure is similar.

I don't have a start.gcode file in that folder, just an example file. I'll put one in. I assume there doesn't need to be any header info since the gcode for an item just starts right in with codes.

It didn't occur to me that doing test extrusions, to make sure it was feeding correctly and such, would carry over an extrusion length into the printing of an item. I noticed the progressive E numbers in the item gcode but figured it would just assume it was at zero when it started.


Thanks again for your help.